research on evolution of human

At the Smithsonian | December 27, 2022

Fourteen Discoveries Made About Human Evolution in 2022

Smithsonian paleoanthropologists reveal the year’s most riveting findings about our close relatives and ancestors

A team led by Laurits Skov and Benjamin Peter from the Max Planck Institute for Evolutionary Anthropology sequenced nuclear, mitochondrial and Y-chromosome DNA of 13 Neanderthal individuals. From these sequences, they determined that two of the Neanderthals represent a father-daughter pair and that another two are cousins.

Ryan McRae and Briana Pobiner

With many projects around the world proceeding despite the Covid-19 pandemic, researchers across a variety of fields made multiple exciting breakthroughs on human origins, gaining more insight into topics ranging from food and drink to interspecies cooperation.

Telling us more about our food, our health, our close relatives and ancestors, and even our animal friends, these 14 new discoveries scientists made this year shed more light on what it means to be human.

Meat, fire and beer: origins of modern food staples

For decades, one of the hallmarks of human evolution has been the presumed shift from a predominantly plant-based diet to one that included significant amounts of meat and animal tissue. Scientists surmised that since meat is generally more nutrient-dense, more meat-eating could have allowed our ancestors, beginning with the emergence of Homo erectus around 2 million years ago, to evolve the large and energetically demanding brains that we associate with our own species.

But the question remained: Did meat consumption actually increase after this time, inferred by stone tool butchery marks on fossilized bones, or is there just more fossil material overall from that period—making it more likely to find these butchery marks?

In January, W. Andrew Barr from George Washington University and colleagues examined all the fossil evidence for butchery in eastern Africa from 1.2 million years ago and older. They concluded that the evidence for increased carnivory in our ancestors is merely an effect of increased sampling of the archaeological record at certain time intervals starting around two million years ago, meaning that there is no strong relationship between eating more meat and the evolution of larger brains in our ancestors.

Well, if it wasn’t meat eating that enabled big brains to evolve, maybe it was cooking?

Cooking makes food easier to digest, allowing for the extraction of more nutrients from food while expending less energy. The earliest evidence for human control of fire dates back to at least one million years ago, but the earliest evidence for using fire to cook food is much more recent.

In November, a team led by Irit Zohar from Tel Aviv University made breakthrough discoveries from the Israeli site Gesher Benot Ya’aqov that pushed this date back to around 600,000 years ago with new evidence for hominins cooking fish. Teeth of a species of carp were subjected to temperatures required to cook fish, but not as hot as temperatures directly inside a fire would be. This indicates the fish were placed above or next to the fire for cooking rather than being discarded in the fire or burned accidentally.

Of course, what good is barbecue without a tasty beverage to wash it down? In December 2021, a team led by Jiajing Wang from Dartmouth University uncovered the oldest known beer production in the world in Egypt. Made of fermented grains, the production of beer is closely linked to the emergence and spread of agricultural societies.

Dating to 5,800 years ago, hundreds of years before Egypt’s first pharaoh, this beer was thick like a porridge rather than watery and probably used for both daily consumption and ritual purposes. Yum?

Animal friends and animal food: origins of domestication and cooperation

Whether for work, companionship or food, domesticated animals make modern human existence possible. But do human impacts on animal communities in a broader sense date back far earlier than evidence for domestication?

In July, a team led by Danielle Fraser from the Canadian Museum of Nature quantified species evenness in North America over the past 20,000 years and found that there were two periods when the diversity of animal communities notably decreased. The first, around 10,000 years ago, was associated with the North American megafauna extinction. The other occurred around 2,000 years ago during a period in which agriculture spread rapidly and population sizes boomed.

This study demonstrates that humans can affect, and have affected, animal communities in indirect ways in addition to hunting and domestication.

When it comes to domesticated animals, perhaps none captures the imagination and our emotions like humankind’s best friend—the dog.

Dogs are also currently the earliest known domesticated animal on earth. A June study led by Anders Bergström and Pontus Skoglund of the Francis Crick Institute looked at genomes of ancient wolves, from whom our species domesticated the modern dog, to try to determine where and when the connection between humans and dogs began.

They found that ancient wolf populations in North America, Europe and Siberia were interconnected with each other in the past rather than being separate populations as they are today, and that all dogs included in the study are most closely related to wolves from eastern Eurasia rather than from western Eurasia.

However, ancient wolves in southwest Eurasia made significant contributions to the genome of dogs originating from the Near East and Africa—either indicating a separate domestication process or, more likely, interbreeding with that additional wolf population early in the process (just as early members of our own species interbred with Neanderthals when we first left Africa).

While this study points strongly to eastern Eurasia as the geographic source of modern dogs, none of the ancient wolf populations studied were the direct ancestor of modern dogs, meaning that the true dog ancestor (or ancestors) is yet to be found.

In addition to companionship, humans also domesticated animals for food and to assist with work. A study in June led by Joris Peters from Ludwig Maximilian University Munich and Greger Larson from the University of Oxford traced the origin of chicken domestication to around 1650 B.C.E. in Thailand, corresponding to the spread of grains (specifically rice and millet). Chickens then appear to follow the grains as they spread around the world as a food source.

Clearly, modern humans owe a lot to our animal friends, and new finds continue to shed light on where, when and how these interspecies interactions first emerged.

New fossils shed light on old ancestors: discoveries from our earliest and most recent evolutionary history

As in previous years, 2022 revealed more fossil finds tied to our human lineage’s earliest history.

One of the first possible hominins, Sahelanthropus tchadensis , dates to around six to seven million years ago and was found in Chad in Central Africa. This species was previously known only by cranial remains and a partial femur, but in August a team led by Guillaume Daver and Franck Guy from the University of Poitiers reinterpreted the femur (upper leg bone) and described two ulnae (forearm bones). These ulnae share many affinities with our ape relatives and suggest that while Sahelanthropus may have been bipedal on the ground, its arms were still well adapted to climbing and clambering in trees.

On the more recent side of prehistory: New fossils of the enigmatic Denisovans , known mostly from their DNA, are starting to tell us more about where they lived and what they looked like. Following up on a Denisovan mandible found in Tibet in 2019, a Denisovan molar was recently discovered in Laos. Dating to between 130,000 to 160,000 years old, this is the first Denisovan fossil found in a geographic area where scientists now know their DNA wound up. Many populations of modern Southeast Asian, Papuan and Filipino people have some Denisovan DNA in them— up to five percent in one Indigenous Filipino group . We’re looking forward to more new finds of Denisovan fossils to tell us more about who they were and what they looked like, as well as when and how they interacted with our own species.

Speaking of species interactions, new finds in February from a cave in southeast France are complicating the story of human-Neanderthal co-occupation of Europe. A team led by Ludovic Slimak from the University of Toulouse unearthed evidence of hominin occupation at a site called Grotte Mandrin in France: First Neanderthals were there, then modern humans, then Neanderthals again before modern humans became the only hominin in Europe.

From both lithic and fossil evidence, this modern human occupation dates to older than 50,000 years ago, almost 10,000 years older than the previous record for modern humans in this region. This evidence tells us that not only did Neanderthals and modern humans live in the same area for a long span of time (potentially implying that our presence in Europe did not drive Neanderthals to extinction), but also that these two species occupied the same site alternately. This extended timespan of interaction could have implications for genetics as well, potentially adding another data point to the where and when of modern human-Neanderthal interbreeding .

Friends and family ties in modern apes and Neanderthals

While most studies of apes focus on groups of only one species at a time, some apes, like chimpanzees and gorillas, do overlap in multiple locations—providing an opportunity to observe the interactions between them. Often when two closely related species overlap in range, their actions are predominantly antagonistic or aggressive toward the other group.

But in the Nouabalé-Ndoki National Park in the Congo Republic, chimpanzees and gorillas have been observed being downright friendly with each other. From the two species foraging in the same tree, to their young playing with each other, to individuals forming lasting friendships, chimps and gorillas have generally gotten along over the 20-year period of study led by Crickette Sanz of Washington University in St. Louis, which was announced in October. This interspecies cooperation may offer a large advantage in deterring predators like leopards and in helping each other find valuable food sources.

While it is relatively straightforward to observe group dynamics in living apes, figuring out how now-extinct early human groups lived and interacted is much trickier, as population-level studies require multiple fossils from the same site at the same time period.

Between two cave sites in southern Siberia (the Chagyrskaya and Okladnikov caves), in October a team led by Laurits Skov and Benjamin Peter from the Max Planck Institute for Evolutionary Anthropology sequenced nuclear, mitochondrial and Y-chromosome DNA of 13 Neanderthal individuals. From these sequences, they determined that two of the Neanderthals represent a father-daughter pair and that another two are cousins.

Additionally, evidence points to one-third of the Neanderthals being part of the same tightly knit community living around 54,000 years ago. Such small-scale resolution is almost unheard of in paleoanthropology. Analysis of the Y-chromosome (passed on through males) and mitochondrial (passed on through females) DNA reveals that the individuals had significantly less diverse Y-chromosome DNA, indicating that Neanderthal females were the ones to relocate to different groups, diversifying the mitochondrial DNA gene pool—in much the same pattern as has been observed in living chimpanzees.

These findings give us new insights into Neanderthal social structure, and potentially even to how interbreeding with our own species may have occurred.

How disease shapes us, and how we evolved to treat it

Modern medicine is thought to have arisen at least by the time of agriculture and large-scale population centers, possibly as a result of their development. More people means more disease, and humans would have looked for new ways to treat diseases. But something as medically complex as limb amputations were only known to occur as far back as 7,000 years ago and were not commonly known until a few hundred years ago, long after the rise of agricultural societies.

However, a new finding out of Borneo in Indonesia pushes this date back to as much as 31,000 years ago. A team led by Tim Maloney from Griffith University in Australia suggests that this individual appears to have had their leg surgically amputated just above the ankle, and then proceeded to live for another six to nine years based on bone remodeling around the amputation site. This evidence implies that modern humans had complex medical knowledge, such as how to locate and sever blood vessels, nerves, muscle tissue and bone, both safely and effectively, long before the advent of agriculture.

Yet, medicinal knowledge is not relegated to our own species. While animals like elephants, bears and other apes have been known to ingest material for medicinal purposes, it was not until this year that a team led by Simone Pika from the University of Osnabrück observed apes using topical ointments for healing . After catching insects, the wild chimpanzees from the Rekambo community in Gabon then squished them between their lips, rubbed the insect in the wound and removed the insect afterward.

The truly groundbreaking part of the study, announced in February, is that the chimpanzees treated not only their own wounds but also other chimps’ wounds. This sort of caring behavior was assumed to be reserved for our own species, but it seems like caring for others in one’s community could have deeper roots in our evolutionary history.

Another new study out in July led by Pascal Gagneux and Ajit Varki of the University of California San Diego looked at the intersection of medicine and genetics to explore why modern humans have developed such a long post-reproductive lifespan.

The “ grandmother hypothesis ” posits that modern humans live well past sexual maturity in order to care for family members, specifically grandchildren. But when did this long lifespan evolve— and how? A specific gene that produces immune receptors (like specialized parts of immune system cells) called CD33 allows modern humans to prevent some side effects of aging, specifically protecting the brain from inflammation and dementia. The gene for these CD33 receptors is not present in Neanderthals or Denisovans, meaning that it could be one advantage our species had over them, but it also means we had to have acquired it on our own rather than inheriting the gene from a common ancestor. One hypothesis this study explored comes from reproductive health: the idea that we evolved these receptors to fight gonorrhea bacteria. The bacterium coats itself in sugars to mimic the human body, and our version of the CD33 receptors can effectively fight it—sparing our reproductive health. This potentially indicates that this adaptation to reproductive health could have been co-opted by the human body to allow for longer lifespans. In other words, we evolved the CD33 receptors to fight gonorrhea, and as a result our bodies could fight against dementia and allow us to become grandparents.

Most notable: a new 2022 Nobel Laureate

While important strides have been made in genetics and human evolution in the past year, the most notable achievement must go to a new Nobel laureate Svante Pääbo . Born in Sweden in 1955, Pääbo has long been a leader in the field of ancient DNA, especially when it comes to humans and our closest relatives.

In 2010, Pääbo’s team deciphered the Neanderthal genome, unlocking a whole new realm of anthropological insight. Pääbo has also been at the forefront of new discoveries in anthropology, including identifying the Denisovans and understanding the genetic relationships among Denisovans, Neanderthals and our own species, as well as identifying the first early human Neanderthal-Denisovan hybrid . For these reasons and more, Pääbo was awarded the 2022 Nobel Prize in Physiology or Medicine, a fantastic way to round out 2022. Congratulations!

A version of this article was originally published on the PLOS SciComm blog.

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Ryan McRae | READ MORE

Dr. Ryan McRae is a paleoanthropologist studying the hominin fossil record on a macroscopic scale. He currently works for the National Museum of Natural History’s Human Origins Program as a contractor focusing on research, education, and outreach, and is an adjunct assistant professor of anatomy at the George Washington University School of Medicine and Health Sciences.

Briana Pobiner | READ MORE

Briana Pobiner is a paleoanthropologist with the National Museum of Natural History’s Human Origins Program . She lead's the program's education and outreach efforts. 

September 1, 2020

15 min read

How Scientists Discovered the Staggering Complexity of Human Evolution

Darwin would be delighted by the story his successors have revealed

By Kate Wong

Pascal Blanchet

I n 1859, 14 years after the founding of this magazine, Charles Darwin published the most important scientific book ever written. On the Origin of Species revolutionized society's understanding of the natural world. Challenging Victorian dogma, Darwin argued that species were not immutable, each one specially created by God. Rather life on Earth, in all its dazzling variety, had evolved through descent from a common ancestor with modification by means of natural selection. But for all of Darwin's brilliant insights into the origins of ants and armadillos, bats and barnacles, one species is conspicuously neglected in the great book: his own. Of Homo sapiens , Darwin made only a passing mention on the third-to-last page of the tome, noting coyly that "light will be thrown on the origin of man and his history." That's it. That is all he wrote about the dawning of the single most consequential species on the planet.

It was not because Darwin thought humans were somehow exempt from evolution. Twelve years later he published a book devoted to that very subject, The Descent of Man . In it, he explained that discussing humans in his earlier treatise would have served only to further prejudice readers against his radical idea. Yet even in this later work, he had little to say about human origins per se, instead focusing on making the case from comparative anatomy, embryology and behavior that, like all species, humans had evolved. The problem was that there was hardly any fossil record of humans to provide evidence of earlier stages of human existence. Back then, "the only thing you knew was what you could reason," says paleoanthropologist Bernard Wood of the George Washington University.

To his credit, Darwin made astute observations about our kind and predictions about our ancient past based on the information that was available to him. He argued that all living humans belong to one species and that its "races" all descended from a single ancestral stock. And pointing to the anatomical similarities between humans and African apes, he concluded that chimpanzees and gorillas were the closest living relatives of humans. Given that relationship, he figured, early human ancestors probably lived in Africa.

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Since then, Wood says, "the evidence has come in." In the past century and a half, science has confirmed Darwin's prediction and pieced together a detailed account of our origins. Paleoanthropologists have recovered fossil hominins (the group that comprises H. sapiens and its extinct relatives) spanning the past seven million years. This extraordinary record shows that hominins indeed got their start in Africa, where they evolved from quadrupedal apes into the upright-walking, nimble-fingered, large-brained creatures we are today.

And the archaeological record of hominin creations, which encompasses roughly half that time, charts their cultural evolution—from early experiments with simple stone tools to the invention of symbols, songs and stories—and maps our ancestors' spread across the globe. The fossils and artifacts demonstrate that for most of the period over which our lineage has been evolving, multiple hominin species walked the earth. Studies of modern and ancient DNA have generated startling insights into what happened when they encountered one another.

Neandertals were the first extinct hominin species to be recognized in the fossil record and the first to yield ancient DNA. Credit: Javier Trueba/Science Source

The human saga, we now understand, is far more intricate than scholars of yore envisioned. The tidy tropes of our prehistory have collapsed under the weight of evidence: there is no single missing link that bridges apes and humankind, no drumbeat march of progress toward a predestined goal. Our story is complicated, messy and random. Yet it still can be accommodated under Darwin's theory of evolution and in fact further validates that framework.

This is not to say scientists have it all figured out. Many questions remain. But whereas the origin of humans was once an uncomfortable speculation in Darwin's big idea, it is now among the best-documented examples of evolution's transformative power.

We humans are strange creatures. We walk upright on two legs and possess supersized brains, we invent tools to meet our every need and express ourselves using symbols, and we have conquered every corner of the planet. For centuries scientists have sought to explain how we came to be, our place in the natural world.

This quest was often distorted by racist ideologies. Consider the era leading up to the birth of Darwin's bombshell theory. In the 1830s, while a young Darwin was making his momentous voyage onboard the Beagle , a movement was underway to promote the idea that the various modern human groups around the globe—races—had separate origins. To build the case for polygenism, as the theory is known, scientists such as Samuel Morton in Philadelphia collected skulls from people across the world and measured their sizes and shapes, falsely believing those attributes to be proxies for intelligence. When they ranked the specimens from superior to inferior, Europeans would conveniently come out on top and Africans on the bottom. "There was a desire to provide scientific justification for political and power structures," says anthropological geneticist Jennifer Raff of the University of Kansas. "It was science in the service of slavery and colonialism."

Although Darwin's work came down firmly on the side of monogenism—the idea that all humans share a common ancestor—it was nonetheless co-opted to support notions about racial superiority. Social Darwinism, for one, misapplied Darwin's ideas about the struggle for existence in natural selection to human society, providing a pseudoscientific rationalization for social injustice and oppression. Darwin himself did not subscribe to such views. In fact, his opposition to slavery might have been a driving force in his research agenda, according to his biographers Adrian Desmond and James Moore.

By the time Darwin published The Descent of Man , in 1871, the idea that humans had evolved from a common ancestor with apes was already gaining traction in the scientific community thanks to books published in the 1860s by English biologist Thomas Henry Huxley and Scottish geologist Charles Lyell. Still, the fossil evidence to support this claim was scant. The only hominin fossils known to science were a handful of remains a few tens of thousands of years old that had been recovered from sites in Europe. Some were H. sapiens; others would eventually be recognized as a separate but very closely related species, Homo neanderthalensis . The implication was that fossils of more apelike human ancestors were out there somewhere in the world, awaiting discovery. But the suggestion by Darwin, like Huxley before him, that those ancestors would be found in Africa met with resistance from scholars who saw Asia as a more civilized birthplace for humankind and emphasized similarities between humans and Asia's gibbons.

Perhaps it should come as no surprise, then, that when the first hominin fossil significantly older and more primitive than those from Europe turned up, it came not from Africa but from Asia. In 1891 Dutch anatomist Eugène Dubois discovered remains on the Indonesian island of Java that he thought belonged to the long-sought missing link between apes and humans. The find, which he named Pithecanthropus erectus , spurred further efforts to root humankind in Asia. (We now know that Dubois's fossil was between 700,000 and one million years old and belonged to a hominin that was much more humanlike than apelike, Homo erectus .)

Two decades later the search turned to Europe. In 1912 amateur archaeologist Charles Dawson reported that he had found a skull with a humanlike cranium and an apelike jaw in an ancient gravel pit near the site of Piltdown in East Sussex, England. Piltdown Man, as the specimen was nicknamed, was a leading contender for the missing link until it was exposed in 1953 as a fraudulent pairing of a modern human skull with an orangutan's lower jaw.

Piltdown so seduced scholars with the prospect of making Europe the seat of human origins that they all but ignored an actual ancient hominin that turned up in Africa, one even older and more apelike than the one Dubois discovered. In 1925, 43 years after Darwin's death, anatomist Raymond Dart published a paper describing a fossil from Taung, South Africa, with an apelike braincase and humanlike teeth. Dart named that fossil—a youngster's skull now known to be around 2.8 million years old— Australopithecus africanus , "the southern ape from Africa." But it would take nearly 20 years for the scientific establishment to accept Dart's argument that the so-called Taung Child was of immense significance: the fossil linked humans to African apes.

Evidence of humanity's African origins has accumulated ever since. Every hominin trace older than 2.1 million years—and there are now quite a few of them—has come from that continent.

Even as fossil discoveries proved Darwin right about the birthplace of humanity, the pattern of our emergence remained elusive. Darwin himself depicted evolution as a branching process in which ancestral species divide into two or more descendant species. But a long-standing tradition of organizing nature hierarchically—one that dates back to Plato and Aristotle's Great Chain of Being—held sway, giving rise to the notion that our evolution unfolded in linear fashion from simple to complex, primitive to modern. Popular imagery reflected and reinforced this idea, from a caricature in Punch's Almanack for 1882 showing a progression from earthworm to Darwin, to the iconic monkey-to-man illustration that appeared in the 1965 Time-Life book Early Man and became known as the March of Progress.

From the rich assortment of fossils and artifacts recovered from around the world in the past century, however, paleoanthropologists can now reconstruct something of the timing and pattern of human evolution. The finds clearly show that this single-file scheme is no longer tenable. Evolution does not march steadily toward predetermined goals. And many hominin specimens belong not in our direct line of ancestry but on side branches of humankind—evolutionary experiments that ended in extinction.

From the outset, our defining traits evolved not in lockstep but piecemeal. Take our mode of locomotion, for example. H. sapiens is what anthropologists call an obligate biped—our bodies are built for walking on two legs on the ground. We can climb trees if we need to, but we have lost the physical adaptations that other primates have to arboreal life. Fragmentary fossils of the oldest known hominins— Sahelanthropus tchadensis from Chad, Orrorin tugenensis from Kenya and Ardipithecus kadabba from Ethiopia—show that our earliest ancestors emerged by around seven million to 5.5 million years ago. Although they are apelike in many respects, all of them exhibit characteristics associated with walking on two legs instead of four. In Sahelanthropus , for example, the hole in the base of the skull through which the spinal cord passes has a forward position suggestive of an upright posture. A bipedal gait may thus have been one of the very first traits that distinguished hominins from ancestral apes.

Yet our forebears appear to have retained traits needed for arboreal locomotion for millions of years after they first evolved the ability to walk on two legs. Australopithecus afarensis , which lived in eastern Africa from 3.85 million to 2.95 million years ago and is famously represented by the skeleton known as Lucy, discovered in 1974, was a capable biped. But it had long, strong arms and curved fingers—features associated with tree climbing. It would be another million years before modern limb proportions evolved and committed hominins to life on the ground, starting with early H. erectus in Africa (sometimes called Homo ergaster ).

The brain evolved on quite a different schedule. Over the course of human evolution, brain size has more than tripled. A comparison of the braincase of A. afarensis with that of the much older Sahelanthropus , however, shows that hardly any of that growth occurred in the first few million years of human evolution. In fact, most of the expansion took place in the past two million years, perhaps enabled by a feedback loop in which advances in technology—stone tools and the like—gave hominins access to more nutritious foods such as meat, which could fuel a larger and thus more energetically demanding brain, which in turn could dream up even better technology, and so on. Shifts in the shape and structure of the brain accompanied these gains, with more real estate allocated to regions involved in language and long-range planning, among other advanced cognitive functions.

This mosaic pattern of hominin evolution in which different body parts evolved at different rates produced some surprising creatures. For instance, Australopithecus sediba from South Africa, dated to 1.98 million years ago, had a humanlike hand attached to an apelike arm, a big birth canal but a small brain, and an advanced ankle bone connected to a primitive heel bone.

Sometimes evolution even doubled back on itself. When one examines a hominin fossil, it can be difficult to discern whether the species retained a primitive trait such as small brain size from an earlier ancestor or whether it lost the characteristic and then re-evolved it. But the strange case of Homo floresiensis may well be an example of the latter. This member of the human family lived on the island of Flores in Indonesia as recently as 50,000 years ago yet looked in many ways like some of the founding members of our genus who lived more than two million years earlier. Not only did H. floresiensis have a small body, but it also possessed a remarkably tiny brain for Homo , about the size of a chimp's. Scientists' best guess is that this species descended from a brawnier, brainer Homo species that got marooned on Flores and evolved its diminutive size as an adaptation to the limited food resources available on its island home. In so doing, H. floresiensis seems to have reversed what researchers once considered a defining trend of Homo 's evolution: the inexorable expansion of the brain. Yet despite its small brain, H. floresiensis still managed to make stone tools, hunt animals for food and cook over fires.

Adding to the complexity of our story, it is now clear that for most of the time over which humans have been evolving, multiple hominin species walked the earth. Between 3.6 million and 3.3 million years ago, for example, at least four varieties of hominins lived in Africa. Paleoanthropologist Yohannes Haile-Selassie of Arizona State University's Institute of Human Origins and his colleagues have recovered remains of two of them, A. afarensis and Australopithecus deyiremeda , as well as a possible third creature known only from a distinctive fossil foot, in an area called Woranso-Mille in Ethiopia's Afar region. How they managed to share the landscape is a subject of current investigation. "Competing species could co-exist if there were plenty of resources or if they were exploiting different parts of the ecosystem," Haile-Selassie says.

Later, between roughly 2.7 million and 1.2 million years ago, representatives of our genus, Homo —large-brained tool users with dainty jaws and teeth—shared the grasslands of southern and eastern Africa with a radically different branch of humanity. Members of the genus Paranthropus , these hominins had massive teeth and jaws, flaring cheekbones and crests atop their heads that anchored powerful chewing muscles. Here the co-existence is somewhat better understood: whereas Homo seems to have evolved to exploit a wide variety of plants and animals for food, Paranthropus specialized in processing tough, fibrous plant foods.

H. sapiens overlapped with other kinds of humans, too. When our species was evolving in Africa 300,000 years ago, several other kinds of hominins also roamed the planet. Some, such as the stocky Neandertals in Eurasia, were very close relatives. Others, including Homo naledi in South Africa and H. erectus in Indonesia, belonged to lineages that diverged from ours in the deep past. Even as recently as 50,000 years ago, hominin diversity was the rule, with the Neandertals, the mysterious Denisovans from Asia, tiny H. floresiensis and another small hominin— Homo luzonensis from the Philippines—all at large.

Such discoveries make for a much more interesting picture of human evolution than the linear account that has dominated our view of life. But they raise a nagging question: How did H. sapiens end up being the sole surviving twig on what was once a luxuriant evolutionary bush?

Here are the facts of the case. We know from fossils found at the site of Jebel Irhoud in Morocco that our species originated in Africa by at least 315,000 years ago. By around 200,000 years ago it began making forays out of Africa, and by 40,000 years ago it had established itself throughout Eurasia. Some of the places H. sapiens colonized were occupied by other hominin species. Eventually the other folks all disappeared. By around 30,000 to 15,000 years ago, with the end of the Neandertals in Europe and the Denisovans in Asia, H. sapiens was alone in the world.

Researchers have often attributed the success of our species to superior cognition. Although the Neandertals actually had slightly larger brains than ours, the archaeological record seemed to indicate that only H. sapiens crafted specialized tools and used symbols, suggesting a capacity for language. Perhaps, the thinking went, H. sapiens won out by virtue of sharper foresight, better technology, more flexible foraging strategies and bigger social networks for support against hard times. Alternatively, some investigators have proposed, maybe H. sapiens waged war on its rivals, exterminating them directly.

But recent discoveries have challenged these scenarios. Neandertal technology, archaeologists have learned, was far more varied and sophisticated than previously thought. Neandertals, too, made jewelry and art, crafting pendants from shells and animal teeth and painting abstract symbols on cave walls. Moreover, they might not have been our only enlightened kin: a 500,000-year-old engraved shell from Java suggests that H. erectus also possessed symbolic thought. If archaic hominins had many of the same mental faculties as H. sapiens , why did the latter prevail?

The conditions under which H. sapiens got its start might have played a role. Fossil and archaeological data suggest that our species mostly stayed in Africa for the first couple of hundred thousand years of its existence. There, some experts argue, it evolved as a population of interconnected subgroups spread across the continent that split up and reunited again and again over millennia, allowing for periods of evolution in isolation followed by opportunities for interbreeding and cultural exchange. This evolutionary upbringing might have honed H. sapiens into an especially adaptable hominin. But that is not the whole story, as we now know from genetics.

Analyses of DNA have revolutionized the study of human evolution. Comparing the human genome with the genomes of the living great apes has shown conclusively that we are most closely related to chimpanzees and bonobos, sharing nearly 99 percent of their DNA. And large-scale studies of DNA from modern-day human populations across the globe have illuminated the origins of modern human variation, overturning the centuries-old notion that races are biologically discrete groups with separate origins. "There have never been pure populations or races," Raff says. Modern human variation is continuous, and most variation exists within populations rather than between them—the product of our demographic history as a species that originated in Africa with populations that mixed continuously as they migrated around the world.

More recently, studies of ancient DNA have cast new light on the world of early H. sapiens as it was when other hominin species were still running around. In the late 1990s geneticists began recovering small amounts of DNA from Neandertal and early H. sapiens fossils. Eventually they succeeded in getting entire genomes not only from Neandertals and early H. sapiens but also from Denisovans, who are known from just a few fragmentary fossils from Siberia and Tibet. By comparing these ancient genomes with modern ones, researchers have found evidence that our own species interbred with these other species. People today carry DNA from Neandertals and Denisovans as a result of these long-ago encounters. Other studies have found evidence of interbreeding between H. sapiens and unknown extinct hominins from Africa and Asia for whom we have no fossils but whose distinctive DNA persists.

Mating with other human species might have aided H. sapiens' success. Studies of organisms ranging from finches to oak trees have shown that hybridization with local species can help colonizing species flourish in novel environments by giving them useful genes. Although scientists have yet to figure out the functions of most of the genes people today carry from extinct hominins, they have pinpointed a few, and the results are intriguing. For instance, Neandertals gave H. sapiens immunity genes that might have helped our species fend off novel pathogens it encountered in Eurasia, and Denisovans contributed a gene that helped people adapt to high altitudes. H. sapiens may be the last hominin standing, but it got a leg up from its extinct cousins.

Scientists have many more pieces of the human-origins puzzle than they once did, but the puzzle is now vastly bigger than it was previously understood to be. Many gaps remain, and some may never close. Take the question of why we evolved such massive brains. At around 1,400 grams, the modern human brain is considerably larger than expected for a primate of our body size. "The singularity is why it's interesting—and why it's impossible to answer scientifically," Wood observes. Some experts have suggested that hominin brains ballooned as they adapted to climate fluctuations between wet and dry conditions, among other explanations. But the problem with trying to answer "why" questions about the evolution of our unique traits, Wood says, is that there is no way to evaluate the proposed explanations empirically: "There isn't a counterfactual. We can't go back to three million years ago and not change the climate."

Other mysteries may yield to further investigation, however. For example, we do not yet know what the last common ancestor of humans and the Pan genus that includes chimps and bonobos looked like. Genomic and fossil data suggest that the two lineages diverged between eight million and 10 million years ago—up to three million years before the oldest known hominin lived—which means that paleoanthropologists may be missing a substantial chunk of our prehistory. And they have hardly any fossils at all of Pan , which has been evolving along its own path just as long as we have. Insights may come from a project currently underway in central Mozambique, where Susana Carvalho and Ren Bobe of the University of Oxford and their colleagues are hunting for fossil primates, including hominins, in sediments older than the ones that yielded Sahelanthropus, Orrorin and Ardipithecus .

Later stages of the human story are riddled with unknowns, too. If H. sapiens was interbreeding with the other hominin species it encountered, as we now know it was, were these groups also exchanging culture? Might H. sapiens have introduced Neandertals to novel hunting technology and artistic traditions—or vice versa? New techniques for retrieving ancient DNA and proteins from otherwise unidentifiable fossils and even cave sediments are helping researchers determine which hominin species were active and when at key archaeological sites.

One wonders where the next discovery will take us in the quest to understand who we are and where we come from. We may have found our place in nature, located our twig on the shrub, but we are still searching for ourselves. We're only human, after all.

Credit: Moritz Stefaner and Christian Lässer For more context, see “ Visualizing 175 Years of Words in Scientific American ”

Kate Wong is an award-winning science writer and senior editor at Scientific American focused on evolution, ecology, anthropology, archaeology, paleontology and animal behavior. She is fascinated by human origins, which she has covered for more than 25 years. Recently she has become obsessed with birds. Her reporting has taken her to caves in France and Croatia that Neandertals once called home, to the shores of Kenya's Lake Turkana in search of the oldest stone tools in the world, to Madagascar on an expedition to unearth ancient mammals and dinosaurs, to the icy waters of Antarctica, where humpback whales feast on krill, and on a "Big Day" race around the state of Connecticut to find as many bird species as possible in 24 hours. Kate is co-author, with Donald Johanson, of Lucy's Legacy: The Quest for Human Origins . She holds a bachelor of science degree in biological anthropology and zoology from the University of Michigan. Follow Wong on X (formerly Twitter) @katewong

Learning the history of evolution and primatology

An exhibition and undergraduate course at Stanford examines the peculiar scrutiny people have placed on their primate relatives to better understand the human condition.

Go to the web site to view the video.

Ever since Charles Darwin claimed in 1871 that humans and other primates share a common ancestor, people have turned to apes in search of an answer to the age-old question: What makes us human?

A new collaboration between Stanford historians  Jessica Riskin  and  Caroline Winterer  takes up this question, and their efforts have culminated in an exhibition in Green Library’s Hohbach Hall,  The Apes & Us: A Century of Representations of Our Closest Relatives , an accompanying  color catalog , a conference, and most recently, a winter quarter  Introductory Seminar  (IntroSem),  HIST 41Q:  The Ape Museum: Exploring the Idea of the Ape in Global History, Science, Art and Film , where students study with original source material to learn how people have viewed and exploited apes in science and across society through the ages.

“Students can see what people around the world in the 19th century were seeing – it was like the moon landing of the 20th century to suggest that all life on Earth is not only connected, but connected over an enormous span of time in which we all changed and evolved,” said Winterer, the William Robertson Coe Professor of History and American Studies in the School of Humanities & Sciences (H&S) and the author of a forthcoming book,  How the New World Became Old: The Deep Time Revolution in America . “As Darwin himself put it, there’s ‘grandeur in this view of life.’ ”

But as her collaboration with Riskin shows, that revelation has been controversial from the beginning. Throughout the 19th and 20th centuries, evolution and primatology have been entangled with race, ideology, and politics.

“When you think historically about the relationship of humans to nonhuman primates, you can connect current ideas and attitudes in science and culture with their now hidden roots in the past,” said Riskin, the Frances and Charles Field Professor of History in H&S.

Gabriel von Max (1840-1915) Abelard und Héloïse , c. 1900-1915, oil on canvas. (Image credit: Courtesy Jack Daulton Collection)

Grappling with a paradigm shift in science

The course and exhibition on the primates and people began after Riskin visited an exhibition in 2021 at the Musée d’Orsay in Paris, The Origins of the World: The Invention of Nature in the Nineteenth Century .

Riskin described some of the items  in an essay for  the New York Review of Books , including the small selection of paintings by the eccentric Czech-Austrian artist Gabriel von Max (1840-1915) showing his pet monkeys assuming human-like positions and roles. Riskin described how von Max – who was an avid Darwinian as well as a painter – anthropomorphized non-human primates to emphasize Darwin’s theories that apes were closely connected to humans.

Riskin’s essay caught the attention of lawyer turned art collector Jack Daulton, who had loaned some von Max paintings to the Musée d’Orsay from his private collection. He contacted Riskin to say he lived near the Stanford campus and asked if Riskin and her students would be interested in seeing other von Max works he owns, to which Riskin enthusiastically responded, yes.

Gabriel von Max, Schlechte Zeiten / Bad Times , 1915, oil on canvas. (Image credit: Courtesy Jack Daulton Collection)

Gabriel von Max (1840-1915), Geburtstagblumen / Birthday Flowers , c. 1890, oil on wood panel. (Image credit: Courtesy Jack Daulton Collection)

Now, some 13 paintings by von Max from Daulton’s collection are on view in Hohbach Hall, including the iconic image of two capuchin monkeys holding one another tenderly, even mournfully. The painting is named after the tragic star-crossed lovers from the 12th century, Abelard and Héloïse.

In addition, there are six glass cases with items from Stanford’s own collections that show the many ways artists and scholars – at Stanford and elsewhere – have examined the differences and similarities between people and primates throughout the 19th and 20th centuries.

For example, there is a case on posture that includes an 1863 copy of Thomas Henry Huxley’s notorious diagram comparing a human skeleton to that of a gorilla, chimpanzee, orangutan, and gibbon as a way to show how our place in nature is in step with apes.

An original copy of Huxley’s diagram is on view at the Apes & Us exhibition. (Image credit: Courtesy Department of Special Collections and University Archives, Stanford University Libraries Collections)

Another case looks at tools and the hands that made them. Some have argued – such as Friederich Engels, a collaborator and close friend of Karl Marx – that the main differentiator between humans and apes is tool use. In the case is a first edition of the book from the Stanford University Archives in which Engels makes his argument.

The exhibit also shows some of the dangerous ways that differences drawn between human and non-human primates have been used to create imaginary racial and class hierarchies.

Francis Galton, Darwin’s cousin, invoked his own interpretation of Darwin’s theory of evolution to found eugenics, a field devoted to “improving” the human population through selective breeding and controlled reproduction.

One case in  The Apes & Us exhibit looks at the role that the evolutionary biologist, ichthyologist, and first president of Stanford, David Starr Jordan, played in the eugenics movement in the United States.

Throughout the cases are various materials from the personal papers of Stephen J. Gould, the influential paleontologist, historian, and evolutionary biologist who spent much of his career rebutting scientific racism and biological deterministic theories. The exhibition calls attention to his 1981 book,  The Mismeasure of Man , in which Gould confronts some of the pervasive tropes about race and intelligence that were prevalent throughout the Victorian era and early 20th century.

There is also a case on primate research at Stanford, including images from the Stanford Outdoor Primate Facility (SOPF) that British primatologist Jane Goodall established in 1974 with David Hamburg, Stanford professor of human biology. Their research became mired in controversy and SOPF closed in 1979.

Learning the history of science and ideas

Studying how humans have interacted with primates in a post-Darwin age is what Winterer calls a “boundary case” where different historical, political, and social perspectives can be brought to bear.

“Whenever you explore a boundary case, you’re also exploring connections,” Winterer said. “When do we erect boundaries between things? When do we create connections across boundaries? We can apply those questions to almost every domain of human thought. The ape and the human boundary or connection is really just one of many such inquiries we can make.”

Crossing in and out of these boundaries was a goal of Riskin’s and Winterer’s IntroSem.

Appropriately titled  The Ape Museum , their course was held in Hohbach Hall, where each week, students interacted with items in the  Apes & U s exhibit.

Students also looked at objects held elsewhere on campus, including at the Stanford University Archaeology Collections, where curator Danielle Raad presented tools and other artifacts made by human ancestors, including some estimated to be between 300,000 to 1.75 million years old.

Francesca Pinney (left) and Megan Liu (right) hold ancient artifacts on a class visit to the Stanford University Archaeology Collections. (Image credit: Danielle Raad)

For freshman Francesca Pinney, holding something so distant in time and space from her was stirring. “History never felt closer,” she said.

The class also visited the Hoover Institution Library & Archives, where  Jean M. Cannon , a research fellow and curator for North American Collections, pulled out propaganda  from their world-renowned poster collection  that showed how apes were used in World War I and II by both Allied and Axis powers to dehumanize the enemy.

Pinney said she was particularly struck by how apes were used in racist ways and the far-reaching consequences that imagery had in society.

“It was disturbing to see some of this propaganda that was so influential in dehumanizing various populations,” Pinney said. “The most haunting part of seeing those pieces of propaganda was [realizing] the prevalence of such disturbing racial components and how successful it was.”

Megan Liu, a sophomore in the course, had a similar reaction when viewing the propaganda posters – some of which were up to 4 feet wide.

“Just seeing them in their original state really showcased how effective it can be because it’s very in your face. It’s very loud. And it’s very bold,” Liu said. “It was a completely different experience seeing them at the Hoover Archive than seeing them [reprinted] on a regular piece of paper.”

The course also featured guest speakers, including course assistant Noah Sveiven, a Stanford senior who talked about his honors thesis research investigating the history of primate science at Stanford and SOPF.

SOPF facility, c. 1974. (Image credit: Stanford University; Archives Peninsula-Times Tribune, Stanford University photographs)

The class also took an optional visit to the San Francisco Zoo, which included a poignant moment for the group with Oscar Jonesy, a 43-year-old silverback western lowland gorilla. When he saw the group entering his enclosure, he approached them and watched them – calmly and intensely – until they disappeared from view.

“It was a stare full of meaning and import somehow,” Riskin recalled of the visit. “That encounter with Oscar gave me a pang to think that he’s lived his whole life in captivity.”

Indeed, an unsettling discomfort can emerge when thinking about the treatment and ethical implications of our closest evolutionary counterparts.

It is that proximity that makes primate science controversial, said Riskin.

“All of our uncertainties, anxieties, convictions, and our whole psyche with regard to humans and humaneness comes out in primate research,” Riskin said.

Apes & Us is on view at Hohbach Hall, located on the first floor of the East Wing of the Green Library, until June 2024.

Stanford Global Studies, which is part of H&S, helped fund the course through  a Course Innovation Award  which supports the development of new courses focused on global topics.

The 1.6 million-year-old discovery that changes what we know about human evolution

New research has pinpointed the likely time in prehistory when humans first began to speak.

Analysis by British archaeologist Steven Mithen suggests that early humans first developed rudimentary language around 1.6 million years ago – somewhere in eastern or southern Africa.

“Humanity’s development of the ability to speak was without doubt the key which made much of subsequent human physical and cultural evolution possible. That’s why dating the emergence of the earliest forms of language is so important,” Dr Mithen, professor of early prehistory at the University of Reading, told The Independent.

Until recently, most human evolution experts thought humans only started speaking around 200,000 years ago. Professor Mithen’s new research, published this month, suggests that rudimentary human language is at least eight times older. His analysis is based on a detailed study of all the available archaeological, paleo-anatomical, genetic, neurological and linguistic evidence.

When combined, all the evidence suggests that the birth of language occurred as part of a suite of human evolution and other developments between two and 1.5 million years ago.

Significantly, human brain size increased particularly rapidly from 2 million BC, especially after 1.5 million BC. Associated with that brain size increase was a reorganisation of the internal structure of the brain – including the first appearance of the area of the frontal lobe, specifically associated with language production and language comprehension. Known to scientists as Broca’s area, it seems to have evolved out of earlier structures responsible for early humanity’s ability to communicate with hand and arm gestures.

New scientific research suggests that the appearance of Broca’s area was also linked to improvements in working memory – a factor crucial to sentence formation. But other evolutionary developments were also crucial for the birth of rudimentary language. The emergence, around 1.8 million years ago, of a more advanced form of bipedalism, together with changes in the shape of the human skull, almost certainly began the process of changing the shape and positioning of the vocal tract, thus making speech possible.

Other key evidence pointing to around 1.6 million BC as the approximate date humans started speaking, comes from the archaeological record. Compared to many other animals, humans were not particularly strong. To survive and prosper, they needed to compensate for that relative physical weakness.

In evolutionary terms, language was almost certainly part of that physical strength compensation strategy. In order to hunt large animals (or, when scavenging, to repel physically strong animal rivals), early humans needed greater group planning and coordination abilities – the development of language would have been crucial in facilitating that. Significantly, date-wise, human hunting began around two million years ago – but seems to have substantially accelerated by around 1.5 million years ago. Around 1.6 million BC also saw the birth and inter-generational cultural transmission of much more sophisticated stone tool technology. That long-term transfer of complex knowledge and skills from generation to generation also strongly implies the existence of speech.

What’s more, linguistic communication was probably crucial in allowing humans to survive in different ecological and climatic zones – it’s probably no coincidence that humans were able to massively accelerate their colonisation of the world around 1.4 million years ago, ie, shortly after the likely date of the birth of language. Language enabled humans to do three key forward-looking things – to conceive of and plan future actions and to pass on knowledge.

“That’s how language changed the human story so profoundly,” said Professor Mithen. His new research, outlined in a new book, The Language Puzzle , published this month, suggests that before around 1.6 million years ago, humans had had a much more limited communication ability – probably just a few dozen different noises and arm gestures which could only be deployed in specific contexts and could not, therefore, be used for forward-planning. For planning, basic grammar and individual words were needed.

Professor Mithen’s research also suggests that there appears to be some continuity between very early human languages and modern ones. He believes that, remarkably, some aspects of that first linguistic development 1.6 million years ago still survive in modern languages today. He is proposing that words, which – through their sounds or length – describe the objects they stand for, were almost certainly among the first words uttered by early humans.

Indeed, future research may be able to tentatively recreate the likely organisation and structure of those first languages. Although the birth of language seems to have occurred around 1.6 million years ago, that birth represented the beginning of linguistic development, not its culmination.

For hundreds of thousands of years, language only very gradually became more complex, ultimately gaining in sophistication after the emergence of anatomically modern humans 150,000 years ago.

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• v.367(1599); 2012 Aug 5

New thinking: the evolution of human cognition

Humans are animals that specialize in thinking and knowing, and our extraordinary cognitive abilities have transformed every aspect of our lives. In contrast to our chimpanzee cousins and Stone Age ancestors, we are complex political, economic, scientific and artistic creatures, living in a vast range of habitats, many of which are our own creation. Research on the evolution of human cognition asks what types of thinking make us such peculiar animals, and how they have been generated by evolutionary processes. New research in this field looks deeper into the evolutionary history of human cognition, and adopts a more multi-disciplinary approach than earlier ‘Evolutionary Psychology’. It is informed by comparisons between humans and a range of primate and non-primate species, and integrates findings from anthropology, archaeology, economics, evolutionary biology, neuroscience, philosophy and psychology. Using these methods, recent research reveals profound commonalities, as well striking differences, between human and non-human minds, and suggests that the evolution of human cognition has been much more gradual and incremental than previously assumed. It accords crucial roles to cultural evolution, techno-social co-evolution and gene–culture co-evolution. These have produced domain-general developmental processes with extraordinary power—power that makes human cognition, and human lives, unique.

1. Introduction

Chimpanzees lead quite interesting lives. They build nests, form alliances with other members of their troop and use simple tools—for example, sticks to fish for termites and stones to open nuts. However, as we are reminded by comedic images of chimpanzees wearing clothes and using computers, the lives of our closest evolutionary relatives are very different from our own. Translated as ‘wise man’, Homo sapiens is an optimistic sobriquet; translated as ‘knowing man’ it is merely descriptive of our species. We are animals that specialize in thinking and knowing—in cognition—and our extraordinary cognitive powers have enabled us to do remarkable things. We have transformed our eating habits with agriculture and cooking, and transformed our habitats with buildings, bridges and roads. Compared with our chimpanzee cousins, we can travel over vast distances, moving our whole bodies in cars, planes and space craft, and moving our minds to yet more remote places with radio telescopes and electron microscopes. We are political and economic animals, negotiating agreements that affect millions of people, and trading instantly in rarefied currencies with completely anonymous strangers in different time zones. We know about time, we understand it to some degree and we can measure it precisely. We communicate with symbols—spoken and written languages—and using these languages, we have developed extensive knowledge of our own history and diversity, and about all aspects of the natural and physical worlds. Our lives are enriched by a fabulous range of beautiful, intricate and provocative objects—by art, architecture, music and dance—and, in addition to developing the weaponry of ‘shock and awe’, we engage in sports, complex rituals that channel and redirect the impulse to fight.

How has evolution produced creatures with minds capable of these remarkable feats? The articles in this theme issue address this question. They represent new thinking about new thinking; leading edge, evidence-based theory about the new forms of cognition that emerged in the course of human evolution. The new theory and evidence come from a range of disciplines, including anthropology, archaeology, economics, evolutionary biology, neuroscience, philosophy and psychology. The new forms of cognition include causal reasoning, imitation, language, metacognition and theory of mind.

Over the past 25 years, research on the evolution of human cognition has been dominated by a type of evolutionary psychology promoted most prominently by Cosmides and Tooby [ 1 – 3 ]. This framework, which I will identify using initial capitals (‘Evolutionary Psychology’), is sometimes known as the ‘Santa Barbara school’ or ‘high church evolutionary psychology’. It suggests that the human mind consists of a large collection of computationally distinct ‘modules’. Each of these modules is a way of thinking that was shaped by natural selection to solve a particular type of problem faced by our Stone Age ancestors—for example, communicating, prey stalking, disease avoidance, mate choice and coalition formation. Evolutionary Psychology's central metaphor is the Swiss Army knife. It casts the evolved human mind as a set of cognitive gadgets, each specialized to learn, remember and reason about particular types of information. Evolutionary Psychology has fulfilled an important function. It has drawn attention to the need to integrate cognitive science with evolutionary biology in order to explain not only how brains and behaviour have evolved, but also the evolution of the ‘middle man’—the cognitive processes, often characterized as computational software, which are instantiated by the brain and control behaviour. However, the ‘massive modularity hypothesis’ has long been an object of criticism [ 4 – 8 ], and the articles in this theme issue represent the emerging alternative view of the evolved human mind.

The alternative view, the ‘new thinking’ that runs through this theme issue, sees the human mind as more like a hand than a Swiss Army knife [ 9 ]. 1 The hand is a multi-purpose instrument of a very different kind to the Swiss Army knife. It has a deep evolutionary history, rooted in the earliest emergence of the pentadactyl limb, and incorporates many genetic adaptations. However, the human hand is also capable of performing a wide and open-ended variety of technical and social functions. It can strip the defensive spines from a piece of fruit, making it safe to eat, but in Thai dancing it can also signal the smallest nuances of emotion. The human hand performs with equal facility a vast array of tasks that natural selection did and did not ‘foresee’.

This article introduces the theme issue by contrasting our ‘new thinking’ with Evolutionary Psychology in relation to three closely related questions about the evolution of human cognition: When did the most important changes take place? How did the changes happen? What have the changes produced?

2. When? beyond the pleistocene past

The first humans, apes of the genus Homo , appeared around the beginning of the Pleistocene geological epoch (1.8 Mya). Evolutionary Psychology has focused on this epoch as the crucible of human cognition. The primary historical aim of Evolutionary Psychology has been to explain the ways in which we think now as genetic adaptations to the reproductive challenges faced by our Stone Age ancestors [ 10 ]. The ‘new thinking’ does not deny that this was an important era in the evolution of human cognition [ 11 ], but it regards the Pleistocene focus as radically insufficient. An adequate understanding of the origins and functions of the human mind, like that of the human skeleton, requires a much longer historical perspective, and to achieve this—to make inferences about the cognitive abilities of extinct, ancestral species—it is necessary to compare contemporary human minds with those of other animals alive today. Accordingly, several of the articles in this theme issue look deep into the evolutionary history of human cognition, examining its roots in the common ancestors of extant eutherian mammals (125 Mya [ 12 ]), primates (85 Mya [ 13 ]) and great apes (15 Mya [ 14 ]).

Barton [ 12 ] uses phylogenetic comparative analysis to examine the evolution of brain structures, the neocortex and cerebellum, in mammals. Phylogenetic comparative analysis is a set of statistical modelling techniques that combines information about relationships of descent among species with data on their phenotypic traits. The models represent inferences about the evolutionary change in traits along the branches of a tree representing the relationships among the species. These models can be used to test hypotheses about which traits are linked, the kinds of selection pressures that shaped the evolution of the traits and, when the traits relate to the brain, about the cognitive capacities that were evolving. The analyses reported by Barton in this theme issue show that the neocortex and the cerebellum have evolved together particularly tightly not only in primates, but in mammals more generally. Traditionally, the neocortex is associated with higher cognition, such as planning and executive control, while the cerebellum is associated with sensorimotor processing of the kind involved in visually guided reaching and grasping. The co-evolution of these structures not just in primates, but over deep evolutionary time—in all mammalian lineages—implies that in evolutionary terms the division between higher and sensorimotor intelligence, between thinking and acting, is artificial. The evolution of human cognition has not merely involved the addition of processes that supervise and control more primitive ways of thinking; it has accelerated an ancient trend towards increasingly powerful and coordinated ‘embodied’ modes of thought.

The article by Barrett and colleagues [ 13 ] also uses new quantitative techniques, draws attention to the continuity between human and non-human cognition, and emphasizes the importance of embodied cognition; of thinking that is not fundamentally distinct from acting. Drawing on the work of Mead and Vygotsky early in the twentieth century, Barrett et al. argue that, in human and non-human primates, thought is a form of social action and interaction. With the emergence of language, individual humans became able explicitly to represent their roles in a social group, but this new ability was integrated with a much older way of coordinating social behaviour, in which participants generate and respond to cues from others but do not have an ‘aerial view’ of group dynamics or of their position within the group. This kind of embodiment hypothesis is sometimes dismissed as impractical, as a rich set of ideas that cannot be cashed out in a feasible strategy for empirical research. Challenging this view, Barrett and colleagues show that the social networks of free-living baboons can be modelled as multi-dimensional objects, and that this approach predicts the effects of natural ‘knock-outs’—the disappearance of group members—on the behaviour of other members of the group.

Whiten & Erdal's [ 14 ] pre-Pleistocene perspective focuses on the comparison of humans with chimpanzees. They identify five major components of the ‘human socio-cognitive niche’, five dimensions on which humans excel—cooperation, egalitarianism, theory of mind, language and culture—and in each case they review evidence that the behavioural/cognitive competence was present to some degree in the common ancestor of humans and chimpanzees. For example, chimpanzees cooperate when hunting and mounting raiding parties on other troops; show signs of egalitarianism when sharing meat and forming coalitions that thwart dominant males; appear to be able to attribute perceptions and goals, if not beliefs and desires, to others; and, in addition to having an extensive repertoire of communicative gestures, chimpanzees use vocalizations in a flexible, context-dependent way to signal information about food and social roles. Whiten & Erdal note that there is a ‘yawning gulf in the cultural achievements of chimpanzees and humans’, but even in this domain they find signs of continuity. Field studies have yielded reports of more than 40 chimpanzee traditions—involving food processing, tool use and various social behaviours—and many of the social learning processes found in humans are also present in other animals, including chimpanzees.

These three articles—by Barton, Barrett et al. and Whiten & Erdal—focus on the deep, pre-Pleistocene history of human cognition. However, emphasizing the importance of this deep historical perspective in new thinking about the evolution of human cognition, all of the papers in the theme issue make comparisons between human and non-human cognitive capacities. For example, Buchsbaum and colleagues [ 15 ] compare causal understanding in human and non-human animals; Sterelny [ 16 ] discusses research on vocal and gestural communication in non-human apes; and Lewis & Laland [ 17 ] compare social learning processes in humans and a range of other animals. Even the article by Shultz et al. [ 11 ], presenting a new analysis of brain size evolution in hominins, focuses on changes in the Pleistocene epoch but interprets them in the light of hypotheses about the selection pressures driving the evolution of cognition in non-human primates and other mammals. They find evidence of punctuated changes in brain size evolution at approximately 100 Kya, 1 and 1.8 Mya, as well as gradual changes in the Homo erectus and Homo sapiens lineages which are not mirrored by distinct variation in global or continental climate records. They argue that their results provide no support for hypotheses suggesting that the evolution of human cognition was driven by environmental aridity or variability. Therefore, it is necessary to reconsider whether extrinsic environmental factors have really been the key drivers of human cognitive evolution or whether intrinsic factors such as social organization, demography or language have been more influential.

(a) Incremental co-evolution

Evolutionary Psychology sometimes gives the impression that new cognitive processes appeared suddenly and fully-formed as a result of lucky genetic mutations and fierce, unimodal selection pressures. This impression is due to not only the relatively short time frame adopted by Evolutionary Psychology, but also its assumption that the mind consists of modules—mutually isolated cognitive processes that do a single job in a special way—and its tendency to focus exclusively on gene-based mechanisms of inheritance. If time was short, cognition was modular, and evolution was mediated solely by genetic mechanisms, it seems that new ways of thinking must have appeared suddenly. However, the articles in this theme issue suggest that time was not short (see §2), that cognition is not massively modular (§4) and—the focus of the present section—that human cognition is a product of gradual, incremental ‘co-evolution’.

Two kinds of co-evolutionary process are discussed in the theme issue. The first kind, which I will call ‘techno-social co-evolution’, occurs when selection pressures favouring the evolution of technical skills (e.g. tool making), and selection pressures favouring the evolution of social skills (e.g. cooperation), become linked by positive feedback loops. For example, innovations in tool-making techniques may create pressure for more intensive cooperation, and more intensive cooperation, in turn, puts a premium on further advances in tool making technology. In principle, this sort of positive feedback loop can promote the evolution of two sets of cognitive processes, one mediating technical skills and the other mediating social skills [ 12 , 14 ], or one set of domain-general cognitive processes underwriting both types of skill [ 4 , 15 , 18 , 19 ].

The second kind of co-evolutionary process, ‘gene-culture co-evolution’, involves the interaction of genetic and non-genetic mechanisms of inheritance, i.e. mechanisms that allow individuals to acquire adaptively-relevant information from others, not via the replication of DNA sequences, but through learning. Lactose tolerance is the most widely cited example of gene-culture co-evolution or ‘dual inheritance’ of a non-cognitive trait [ 20 ]. The ability to digest the lactose found in milk, not only in infancy but also in adulthood, is common in Europe and western Asia, but rare in people from the Far East. This geographical distribution is thought to be due to a gene–culture co-evolutionary process in which some historical populations started dairy farming, making milk plentifully available as a source of nutrients. This meant that the small number of people in those populations who had the genes enabling them to digest lactose in adulthood, and thereby to exploit this resource, out-reproduced others in the population who lacked those genes. As the proportion of lactose-tolerant adults increased, the demand for dairy products increased, further promoting dairying practices and, in turn, demand for dairy products. Thus, there has been co-evolutionary positive feedback between dairying (a culturally inherited set of characteristics) and lactose tolerance (a genetically inherited characteristic).

Sterelny [ 16 ] assigns a fundamental role to techno-social co-evolution in the emergence of human language. He uses archaeological evidence to argue that, by 2–2.5 Mya, techno-social co-evolution was already making hominins into co-operative foragers. Increased environmental variability had selected for improvements in both technical skills (e.g. to exploit dry season food resources) and co-operative social skills (e.g. to guard against predation in more exposed environments). Supporting a ‘gesture-first’ model of language evolution, in which vocal language evolved from complex gestural communication, Sterelny argues that the improvements in technical (extractive foraging) and social skills (gestural communication) were mediated by common cognitive processes—processes that encode and control complex sequences of action. Therefore, pressure for improvement in technical competence enhanced social as well as technical skills, and vice versa, creating a positive feedback loop that culminated in the appearance of fully syntactic vocal communication. Barton's phylogenetic comparative analyses of mammalian brain evolution converge on a very similar conclusion about the co-evolution of technical and social skills [ 12 ].

In their article, also concerned with language, Jablonka et al . [ 19 ] discuss both techno-social and gene–culture co-evolution. In the former case, like Sterelny, they argue that selection pressures for technical (tool making) and social (alloparenting) skills are likely to have fostered the evolution of an overlapping set of cognitive processes. However, rather than emphasizing the common requirement for encoding of complex sequences, they point out that learning to make complex tools and to alloparent both require the kind of inhibitory control that enables patience and social tolerance and reshapes human emotions. Turning to gene–culture co-evolution, Jablonka et al. review several recent theories suggesting that various aspects of language were initially invented and inherited as cultural conventions, and were later ‘genetically assimilated’. Their own view is distinctive in two respects: it highlights ways in which human cognition has adapted to language, not merely language to cognition, and, via the ‘assimilate-and-stretch’ principle, stresses that genetic assimilation makes room for further learning. Thus, when a previously learned linguistic trait, X, has been genetically assimilated—when it develops with minimal environmental input—this frees-up resources allowing a new linguistic trait, Y, to be learned.

(b) Cultural evolution

In contrast to Evolutionary Psychology [ 21 ], new thinking about the evolution of human cognition assigns an important role to cultural evolution. Godfrey-Smith [ 22 ] distinguishes three types of cultural evolution: Darwinian imitation (micro level), cumulative cultural adaptation (meso) and cultural phylogenetic change (macro). In the first, change occurs through differential copying of instances of cultural variants. The second and third allow a greater variety of processes at the micro-level, but make strong empirical commitments on other matters. For example, cumulative cultural adaptation requires a gradualist mode of change. The three types of model have different explanatory potential. For example, Darwinian imitation models can explain the distribution of cultural variants in a population over time, whereas cumulative cultural adaptation models can explain origins: how a complex cultural artefact, such as a canoe, could ever have been invented. Godfrey-Smith shows that different cognitive profiles are required for different types of cultural evolution. Surprisingly, Darwinian imitation requires that individuals are not too ‘smart’—that they are not too intelligently choosy about the variants that they copy (see also [ 23 ]). Cumulative cultural adaptation models require social cognitive processes that enable the decisions of a group to be better than the aggregate of the group members' decisions. Frith's article suggests that these processes are likely to be metacognitive [ 24 ].

Lewis & Laland [ 17 ] use simulations to test the widely held assumption that cumulative cultural evolution—progressive improvement or elaboration of cultural traits—requires cultural variants to be transmitted over many cultural generations with minimal modification. In Godfrey-Smith's terms [ 22 ], this kind of longevity and fidelity preserves ‘parent–offspring relations’ between cultural entities. Lewis and Laland's modelling confirms the importance for cultural evolution of cognitive processes that support transmission fidelity. It also suggests that progress in cumulative culture depends critically on the kind of creative thought that enables cultural variants to be combined in novel ways. Compared with ‘novel invention’ (creating a new variant from scratch) and ‘modification’ (tinkering with an existing variant), new combinations of variants had a much more substantial effect on the rate of cumulative cultural change observed in their models.

Evolutionary psychologists, and even many researchers who emphasize the power of cultural evolution, assume that genetic evolution produced and maintains the core cognitive processes that enable cultural inheritance. Heyes [ 18 ] questions this assumption, using evidence from comparative psychology, developmental psychology and cognitive neuroscience, to argue that the development of imitation and other processes of social learning is remarkably similar to the development of literacy, and that the cognitive processes enabling cultural inheritance are themselves culturally inherited.

Even if cultural evolution is a major force shaping human lives, there are certainly cases where cultural change has not overcome limitations on human cognition imposed by genetic evolution. Dunbar [ 25 ] examines one of these cases in detail. He argues that constraints on time and social cognition, shared with other primates, currently prevent us from using social-networking sites (such as Facebook) to expand the range of people with whom we have enriching social relationships.

4. What? domain-general developmental mechanisms

The final major contrast between ‘new thinking’ and ‘old thinking’ about the evolution of human cognition concerns the unique features of the human mind. Evolutionary Psychology suggested that, in contrast to our primate relatives, we have a range of distinctive, special-purpose cognitive gadgets or modules, each responsible for thinking about a particular kind of technical or social problem that confronted our Stone Age ancestors. Experience was assumed to play a limited role in the development of these modules. Many of the articles in this theme issue present a very different view. They suggest that humans are born with extraordinarily powerful cognitive-developmental mechanisms. These mechanisms are domain-general—they use a common set of computations to process information from a broad range of technical and social domains—and they use experience, especially sociocultural experience, to forge new, more domain-specific cognitive-developmental mechanisms of the kinds that control tool-making, mentalizing, planning and imitating the actions of others. The genetically inherited cognitive-developmental mechanisms use computational processes that are also present in other animals, but they are uniquely powerful in their range, capacity and flexibility.

This aspect of the ‘new thinking’ is most fully articulated in the articles by Heyes [ 18 ], and by Buchsbaum et al. [ 15 ]. Heyes focuses on associative learning, an evolutionarily ancient domain-general developmental mechanism, and on the role that it plays in constructing the capacity to imitate. Buchsbaum et al. focus on causal learning, a domain-general developmental mechanism based on probabilistic models and Bayesian inference. They highlight evidence that evolution has protracted the period of juvenile dependence in humans, relative to that of other animals, and argue that one of the major functions of our extended childhood is to allow us to use causal learning to build capacities for tool making, theory of mind and future planning about counterfactuals. In support of this hypothesis, they present new data that link causal learning with pretend play. In 3 to 4-year-old children, counterfactual reasoning transfers from ‘real’ to ‘pretend’ contexts.

Key elements of the domain-generality view are also evident in the articles by Barrett et al. [ 13 ], Jablonka et al. [ 19 ], Sterelny [ 16 ] and Frith [ 24 ]. Barrett and colleagues emphasize the importance of social experience in shaping cognitive processes. Jablonka et al. and Sterelny argue that, as a result of techno-social co-evolution, humans have ‘two-for-one’ cognitive developmental mechanisms; processes that facilitate learning of both extractive foraging and social skills. Even Barton [ 12 ], although clear in denying that there could be no ‘general’ (non-technical, non-social) selection pressure, suggests that the combination of technical and social pressures has produced sensorimotor or ‘embodied’ cognitive processes that tackle technical and social problems using an overlapping set of computations.

Frith [ 24 ] reviews recent research in psychology and cognitive neuroscience on ‘metacognition’, the processes by which we monitor and control our own cognitive processes and those of others. He distinguishes implicit metacognition, which allows humans and other animals to take account of knowledge and intentions automatically, from explicit metacognition, which involves conscious awareness and depends on a capacity for complex communication. Frith argues that the capacity for explicit metacognition is uniquely human, and implies that the capacity is a genetic adaptation. Since metacognition is relatively domain-specific (it is thinking about thinking), this indicates that he is sympathetic to the idea that mentalizing is a module. However, in line with the view that humans have uniquely powerful cognitive-developmental mechanisms, Frith also suggests that, when we are born, ‘the content of explicit meta-cognition is a blank slate on which we learn to write our experiences. And what we learn to write there is determined largely through social interactions’.

Robalino & Robson [ 26 ] also discuss the evolution of theory of mind, bringing together research on this topic from economics and from cognitive neuroscience. They provide a detailed summary of the way in which game theorists have developed the work of Harsanyi and Aumann to produce hierarchical models of theory of mind using Bayesian decision theory. These models are impressively formal and precise, but they do not fully predict the behaviour of fallible agents in real social interactions. Robalino and Robson identify a number of ways in which interdisciplinary research could produce models that are both precise and empirically grounded; an understanding of the bounded rationality of theory of mind.

5. Concluding remarks

We have seen that, in comparison with Evolutionary Psychology, new thinking about the evolution of human cognition: (i) takes a longer historical perspective, and therefore a more comparative approach, (ii) highlights the importance of co-evolution and cultural evolution in generating gradual, incremental change and (iii) suggests that humans are endowed with uniquely powerful, domain-general cognitive-developmental mechanisms, rather than with cognitive modules. The final article in the theme issue asks whether these contrasts can be encapsulated using the concept of innateness. Perhaps the new thinking denies that distinctively human cognitive processes are innate, and is therefore less ‘evolutionary’ than Evolutionary Psychology. In the final article in this theme issue, Shea [ 27 ] argues that this is not a helpful or legitimate way of characterizing the direction in which the field is moving. The concept of innateness cannot capture the current trend because it implies connections and distinctions that the new thinking rejects. For example, the innateness concept implies that the development of adaptations is experience-independent, and that there is a dichotomy between individuals learning for themselves and relying on genetic information. Shea proposes that the main thrust of the new thinking can instead be captured by the concept of ‘inherited representation’. This concept embraces three ways in which natural selection builds up information that is transmitted down the generations and used to produce adaptive phenotypes: genetic, epigenetic and cultural inheritance. The new thinking highlights the central role of learning and rich interactions with the physical and social environment for the development of human psychological capacities. The concept of inherited representation makes clear how this is compatible with a profoundly evolutionary focus; the new thinking points to natural selection as an important source of the adaptively relevant information encapsulated in human psychological traits, and assigns a central role to cultural evolution and gene–culture co-evolution in producing the distinctively human cognitive and social phenotypes that differ so strikingly from those of our closest primate relatives.

Acknowledgements

The papers in this Theme Issue were presented at a workshop entitled ‘New Thinking: Advances in the Study of Human Cognitive Evolution’, held at the University of Oxford on 23–24 June 2011. The editors of the theme issue (C.H. and U.F.) thank the co-organizers of that meeting, Susanne Shultz and Nicola Byrom, and those who provided additional help with the arrangements: Robin Dunbar, Humaira Erfan-Ahmed, Jennifer Lau, Emma Nelson, Kit Opie, Ellie Pearce and Rafael Wlodarski. We are grateful for the financial support provided by All Souls College, Oxford; The British Academy; Guarantors of Brain; and Magdalen College, Oxford. The workshop concluded a ‘theme term’ on the Evolution of Human Cognition generously supported by the Warden and Fellows of All Souls College.

1 The hand metaphor emerged from discussion among the participants in the Evolution of Human Cognition project based at All Souls College, Oxford in May/June 2011 (Robert Barton, Alison Gopnik, Russell Gray, Cecilia Heyes, Eva Jablonka, Arthur Robson, Kim Sterelny), but it was ultimately the product of Eva Jablonka's dexterous mind.

First view of centromere variation and evolution

Critical for accurate transmission of chromosomes during cell division, centromeres differ vastly in size, structure and epigenetic makeup.

A genomic study of human and selected nonhuman primate centromeres has revealed their unimaginable diversity and speed of evolutionary change.

In cell genetics, a centromere is the spot where two sister chromatids attach. A chromatid is one-half of a duplicated chromosome. United pairs of chromosomes have identifiable shapes because centromeres are not in a uniform position. As a cell prepares to divide, the machinery to separate and segregate chromosomes goes into action at each centromere location.

Unless the genetic material is distributed correctly between the two resulting cells, problems can arise. These include cancer, congenital disorders such as Down syndrome, and the inability of a fertilized cell to grow into a baby.

Although centromeres are vital to proper cell replication, the complexity of their genomic organization had been almost impossible to study. The lack of centromere sequences hindered exploration of how these regions help maintain genetic integrity.

Today, advances in long-read genome sequencing technologies, refined computerized genome assembly algorithms, and improved genome databases are enabling scientists to realize how greatly centromeres differ in size and structure. This opens new avenues toward figuring out what these differences might mean.

A first look at the factors behind the vast variations in centromeres is reported today, April 3, in Nature . The findings suggest that centromeres are likely highly individualized among people. A set of centromeres might even be a personal signature, just as we each have characteristic voice patterns, iris colorations and fingerprints that distinguish us from one another.

It's not yet known if certain centromere variations might make people susceptible to particular diseases.

Only the human X chromosome appears to be mostly immutable, with very similar sequences and structure across a diversity of humans.

The lead author of the Nature report is Glennis Logsdon, a recent postdoctoral scholar in Evan Eichler's genomic science lab at the University of Washington School of Medicine in Seattle. Logsdon is now a faculty member at the Perelman School of Medicine at the University of Pennsylvania. Eichler, who is also a Howard Hughes Medical Institute Investigator and a member of the Brotman Baty Institute for Precision Medicine, is the senior and corresponding author.

"This recent research is a direct application of both the Human Pangenome Reference Consortium and the Telomere-to-Telomere (T2T) sequencing efforts to provide new biological insights into complex regions of the human genome critical for chromosome segregation," noted Eichler. He is known for his work on genome evolution and its potential to create new functions and also for studies of genetic instability associated with disease.

To capture information on how human centromeres might have evolved, the team compared human genetic sequences of two completely sequenced human centromeres with those of some nonhuman primates. These were the chimpanzee and the orangutan, which are great apes and closely related species to humans, and the macaque, an Old World monkey and a more distant relative.

The scientists discovered that centromeres have been evolving much faster than other unique portions of the human genome. They are among the most mutation-prone regions of the human genome. The researchers also found that the unique sequences and structure of centromeres were the culmination of different evolutionary forces moving at different rates.

"The rapid mutation of the centromeric regions of the genome, along with their various mutation rates, has led to their diverse structure and organization," Logsdon noted. It was surprising to learn, the scientists said, that such vital areas of the genome were subject to swift changes, because, in general, critical functions tend to be genetically conserved.

The scientists plan to expand these initial efforts by developing more genetic maps of centromeres in diverse human genomes and across various organs and tissues, and to perform multigeneration family studies of centromere sequences. The complete sequence of centromeres from other nonhuman primates will provide a better model of the evolutionary forces shaping these regions.

Peering into the future, Logsdon and her team hope someday to apply their findings on centromeres to the design and engineering of customized human artificial chromosomes to transform medical science. Several years ago, Logsdon and her mentors worked on efforts to develop human artificial chromosomes that bypass centromeric DNA, which had then posed a constraint to mammalian synthetic genome research. Logsdon and others recently published another study last week in Science, which showed that enlarging the artificial chromosome DNA vector allowed for efficient formation of human artificial chromosomes in cells.

The centromere studies reported today were supported by funding from the National Institutes of Health National Human Genome Research Institute (R01 HG010169); National Institute of General Medical Sciences (K99 GM147352 ); National Cancer Institute (R01 CA266339); Intramural Research Program of the National Human Genome Research Institute; Shanghai Jiao Tong University 2030 Program (WH510363001-7); Center for Integration in Science of the Ministry of Aliyah, Israel; and the Howard Hughes Medical Institute. This work utilized the computational resources of the National Institutes of Health High Performance Computing Biowulf Linux cluster.

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Materials provided by University of Washington School of Medicine/UW Medicine . Note: Content may be edited for style and length.

Journal Reference :

• Glennis A. Logsdon, Allison N. Rozanski, Fedor Ryabov, Tamara Potapova, Valery A. Shepelev, Claudia R. Catacchio, David Porubsky, Yafei Mao, DongAhn Yoo, Mikko Rautiainen, Sergey Koren, Sergey Nurk, Julian K. Lucas, Kendra Hoekzema, Katherine M. Munson, Jennifer L. Gerton, Adam M. Phillippy, Mario Ventura, Ivan A. Alexandrov, Evan E. Eichler. The variation and evolution of complete human centromeres . Nature , 2024; DOI: 10.1038/s41586-024-07278-3

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Anthropology professor co-authors new book about the history and evolution of human infectious diseases

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The Covid-19 pandemic caught most nations and their public health systems by surprise. Yet there has always been considerable historical evidence to understand the emergence of infectious diseases that should have left us more prepared than we were. 

That’s the subject of the recently released second edition of Emerging Infections: Three Epidemiological Transitions from Prehistory to the Present (Oxford University Press), which was co-authored by Ron Barrett , associate professor of anthropology. Among the first comprehensive syntheses of both the societal and environmental drivers of infectious diseases in humans, Emerging Infections employs a multidisciplinary approach to lay out this rich history. Professor Barrett shares what we know and how it can be applied in order to better prepare for the inevitable emergence of the next major transmissible disease.   

You point out that recent outbreaks of Ebola, drug resistant TB, and Covid-19 took us by surprise, but we should have been preparing for them a long time ago. What essential truths got missed? 

The essential truths have to do with recurring themes in the history of infectious diseases in human societies. The outbreaks you just mentioned are quite novel, but the determinants — the factors that brought them into being — are quite old and recurring. We should be aware of these recurring factors so we can better prepare for whatever the next pandemic is going to be. 

Disease outbreaks over the last 11,000 years have largely been determined by changes in patterns of human activity. The book breaks this activity down into three distinct periods known as epidemiological transitions. The first transition began 11,000 years ago in the late Paleolithic. What are its characteristics? 

The first epidemiological transition occurred with the intensification of agriculture as our primary form of subsistence. It wasn’t that human beings hadn’t farmed before, but when we began to permanently settle and intensively farm in single areas, create irrigation systems, and domesticate animals, it created a series of social lifestyle changes. 

Those changes included increased population density and closer proximity to animals over extended periods of time. Those animals carried novel infectious diseases. Many of the diseases we face today are descendants of these diseases. 

With regards to nutrition, the farming of cereal grains brought an important source of food energy for us, but it often came at the expense of dietary diversity. We see a marked increase in nutritional problems that are reflected in ancient skeletons. Unfortunately, we know all too well from living populations that any form of malnutrition is almost almost always accompanied by acute infectious diseases. 

For more than 100,000 years, Homo sapiens lived in small social groups. Large populations were not conducive when we were mobile and subsisting on hunting and gathering. You don’t get a lot of social hierarchy with small groups because if people don’t get along, they split apart. With larger-scale societies, we start seeing specialization of labor, social hierarchies and differential distribution of essential resources. These social changes brought differential health outcomes that contributed to the rise of acute infectious diseases. 

The second epidemiological transition coincided with the Industrial Revolution beginning in the late 19th century in Western Europe and North America. What changed in terms of the relationship between humans and diseases? 

Essentially, this second transition is a reversal in some of the changes that came with agriculture thousands of years earlier. New farming methods and transportation improvements brought greater varieties of food resources to more people, even those with lower incomes. This is not to say that poverty wasn’t a problem, it absolutely was, but there were significant dietary improvements overall. We see this as people of all classes began growing taller at much faster rates than could be explained by genetic factors. 

Improvements in water quality, wet and dry sanitation, and waste disposal had major impacts as well. Here, industrial societies were learning how to live healthier in large and densely populated urban areas. It didn’t happen right away, but in the late 19th century, we began seeing housing reforms that brought even greater infectious disease declines. 

Many of us believe that these health improvements were primarily due to biomedical discoveries, but this was not the case. Germ theory eventually led to effective antimicrobials and many of the vaccines we see today, but most of these discoveries did not happen until well into the 20th Century. Until then, the largest declines in infectious disease had more to do with non-pharmacological factors: changes in nutrition, changes in the way we were living together, and changes in the way that essential resources were distributed. 

Lastly, the third transition is the one we’re in today. It began not long ago in the last quarter of the 20th century. What important shifts happened here? 

Today, we see a significant rise in what are called syndemics, synergistic interactions between multiple diseases. Especially relevant are the interactions between chronic noninfectious conditions such as diabetes, heart and lung diseases, and acute infectious diseases such as TB, influenza, and of course, the highly pathogenic coronavirus infections. With regards to Covid-19, the highest mortality has occurred among older people with preexisting noninfectious conditions as well as depressed immune systems. 

Globalization is the other major shift. While the globalization of human populations has been occurring since about the 5th century, C.E., this process has greatly accelerated in the last 50 years with improvements in communications and transportation, as well as the growing interdependence of economic systems. We are now living in what is effectively a single-human disease ecology, which means that outbreaks in any society or any part of the world can quickly become a threat to everyone else. 

As you point out in the book, the primary lesson is that all of our infections, past and present, are essentially social diseases. If we acknowledge this fact, what do you recommend we change? 

One of the most important things is that we need systems for the active detection of infectious diseases, and small decentralized clinics that can provide basic public health services.

Disease surveillance comes in two flavors: active and passive detection. Passive detection is what most nations do – wait for somebody to walk into an E.R. or a doctor’s office before testing them. But the passive approach does not give us a representative picture of what is happening to the population as a whole. We can only know this with active detection, when health workers go out into the general population and randomly test for all manner of infections. We have the technology to do this now, and we can do so cheaply and at very large scales. Minimally invasive health surveillance is going to be essential for us to have a sense of what’s out there. 

Part and parcel to active detection is a well-functioning public health infrastructure. 

By this I am not calling for a particular type of healthcare system; societies can hammer out those kinds of issues. But people need not argue about having small, neighborhood clinics that are staffed by people who are known to their surrounding communities. These clinics can provide early information to health authorities about potential outbreaks. They can also serve as trusted sources of medical information for their patients. 

Trust is essential during an epidemic. I don’t think it’s realistic to expect people to trust national figures on public television, regardless of what conspiracy theories they may or may not have. But I do think they’re  more likely to trust their own local health providers.  

These kinds of lessons are very practical, and they should resonate with most people regardless of political background. Without this kind of common ground, we will not have the kinds of lasting health reforms that will be necessary to deal with future epidemics.

April 9 2024

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• Published: 29 July 2021

How will our understanding of human development evolve over the next 10 years

• Ali H. Brivanlou   ORCID: orcid.org/0000-0002-1761-280X 1 ,
• Nicolas Rivron   ORCID: orcid.org/0000-0003-1590-5964 2 &
• Norbert Gleicher   ORCID: orcid.org/0000-0002-0202-4167 3 , 4 , 5  

Nature Communications volume  12 , Article number:  4614 ( 2021 ) Cite this article

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• Embryogenesis

In the next 10 years, the continued exploration of human embryology holds promise to revolutionize regenerative and reproductive medicine with important societal consequences. In this Comment we speculate on the evolution of recent advances made and describe emerging technologies for basic research, their potential clinical applications, and, importantly, the ethical frameworks in which they must be considered.

Future milestones in basic science of human development

In its infancy only a few years ago, the basic understanding of human development will continue its progress. The future holds significant promise for transformative discoveries about the origin of humans, driven by the development of new tools that synergistically combine biology with principles of physics, engineering and artificial intelligence (AI), within an appropriate ethical framework.

We can expect the deciphering of the complete molecular signatures of every human cell forming the conceptus (until gastrulation time 1 and during fetal stages), allowing for the discovery of additional human-specific genetic features, molecular networks, cells and tissue types. This information will unveil human-specific functions, even in transient organs and tissues, such as our fetal gill, tail, or the subplate of our primitive brain 2 , which in turn will highlight evolutionary differences with classical model systems.

Ethical discussions regarding the utilization of genome editing technologies will, unquestionably, be at centerstage, due to their potential to illuminate the functions of (epi)genetics in development and diseases. How central this subject is to scientific progress, not only in reproductive biology and medicine, is well demonstrated by several recent reports including the conjoint one from the U.S. National Academy of Medicine and the Royal Society of the U.K., titled “ Heritable Human Genome Editing .” 3 These reports establish an initial framework for governments and other regulatory bodies worldwide to evaluate research involving human germline editing. In the next decade, this research will remain within the in vitro realm (e.g., human gametes or embryos cultured in vitro). Movement of germline editing into clinical practice can and should only occur after the steps outlined in the reports cited above have taken place. Therefore, it is currently difficult to imagine that germ line gene editing will be ethically accepted and technically ready for clinical practice within the next 10 years.

However, assessing the safety and efficacy of numerous biomedical approaches (e.g., to improve in vitro fertilization (IVF), contraception, and understand monogenic diseases) will require the ability to culture human embryos for a few weeks in vitro. We thus predict that in the next decade human embryos will likely be allowed to be maintained in vitro beyond the current 14-day limit according to guidelines generated by the appropriate oversight committee, as benefits linked to knowledge gained and potential clinical applications from such a step will outweigh the societal and cultural concerns that can still be held.

As an ethical alternative to the use of human and animal embryos, the emerging field of embryo modeling will form, through the self-organization of stem cells, increasingly sophisticated in vitro substitutes. Within the next decade, embryo models that do not attempt to recapitulate the development of the entire conceptus (e.g., gastruloids ) will progress toward the first trimester, thus providing, for the first time, a blueprint of our early developmental origins (e.g., body axis formation, somitogenesis). In parallel, embryo models mimicking the entire conceptus (e.g., blastoids) will be combined, as in vitro discovery platforms, with the uterus organoid to expose the hidden processes of implantation and development that occur within the first weeks post fertilization. Although it is not conceivable to use human blastoids in reproduction in the coming ten years 4 , such in vitro platforms will guide drug and biomedical discoveries to better manage early pregnancy. Altogether, by recapitulating events that are otherwise impossible to access, embryo models will provide an ethical alternative toward addressing global health issues of family planning (e.g., high early pregnancy loss, contraception), developmental diseases (e.g., monogenic), and of their prevention according to the developmental origins of health and diseases.

Our basic knowledge of human organ generation and regeneration will also evolve. The combinations of primordial organoids through bottom-up approaches 5 supported by engineered environments (e.g., hydrogels, microfluidics) 6 and vasculatures 7 will generate more standardized, mature and functional organs of increased volumes and complexities. Achieving the in vitro maturation of such complex organ systems using autologous human induced pluripotent stem cells (iPSCs) will open possibilities for more predictive and personalized drug-screens, and in the long-term, for therapeutic transplants. These systems will also shed light on currently inaccessible fundamental knowledge about human organogenesis and physiology, including new ontologies, which, through careful comparisons to species endowed with enhanced regenerative capacities (e.g., axolotl 8 ) will reveal therapeutic targets to unleash potential human regenerative capacities, thus paving the way toward regenerative medicine’s long-term goals in humans.

A new horizon for reproductive medicine induced by basic research

We foresee progress for the first clinical applications of burgeoning technologies that emerged over the last decade and for the development of clinical protocols that will revolutionize science and society.

In reproductive medicine one can foresee successful in vitro culture of primordial follicles toward maturity. Currently, only one out of 400 follicles will mature to give rise to a fertilizable oocyte, while the rest undergoes degeneration and apoptosis before reaching ovulation. Since this is a highly wasteful process, an improved in vitro maturation process would radically change current infertility treatments. Even at young ages, single egg retrieval currently only yields on average between 10 and 15 oocytes. A single small cortical ovarian biopsy at relatively young ages, in contrast, could offer a woman a potential egg pool of hundreds of oocytes. Improvement of in vitro primordial follicle culture could therefore virtually secure future conception for women at almost all ages. Women will then be afforded the same privilege as males, who, because of continuous spermatogenesis, are assured of genetic paternity into advanced age. Such a development would, of course, relieve women of considerable socio-biological pressures, while dramatically increasing gender equality. Studies to reach this goal are already underway 9 .

Further improvement of currently still sub-optimum cryopreservation methods of ovarian tissue, embryos and oocytes will provide security for women about to undergo often destructive cancer therapies or provide women of older ages the chance to have children later in life. In science, the resolution of one question, only leads to one or more new ones. Here, the most obvious arising question that will have to be answered is, up to which age should motherhood then be pursued in the view of child welfare?

Currently increasingly recognized clinical limitations of preimplantation genetic testing for aneuploidy (PGT-A) 10 , 11 , also addressed in our 10-year retrospective Comment, do not mean that novel cellular and molecular diagnostic approaches for embryo selection in IVF may not succeed in providing a more precise ranking methodology to evaluate embryo quality and live birth chances. As deep neural networks and AI, integrated with transcriptomic signatures, are increasingly introduced to IVF practice, progress can be expected 12 .

Another theme entering the field is the influences of the environment on the reproductive ecosystem. Notably, the role of the microbiome, which has been attracting increasing attention throughout medicine, and will, undoubtedly, also receive more prominent attention in reproductive sciences 13 . Additionally, the cellular and molecular mechanism underlying immune-tolerance pathways that are induced by the immune system in order to tolerate implantation of and invasion by a semi-allogeneic paternal graft will be, finally, elucidated 14 . Given the high prevalence of mosaicism, chromosomal instability in human preimplantation-stage embryos, it is tempting to hypothesize that what represents a detrimental and unlimited process in malignancies, may be a beneficial, yet only temporary, process in embryo implantation. Therefore, establishing what stops invasiveness in early pregnancy (except in cases of choriocarcinoma) may, therefore, have relevance for both reproductive and cancer biology.

To model reproductive diseases in a dish, stem cell-derived ovaries and testes will be modified using CRIPR/Cas9 genome editing tools in a manner similar to standardized organoids, described in our accompanying Comment 15 . These structures will be used in highly quantitative platforms to conduct high-throughput screens and identify drug candidates that can rescue any reproductive aberrance. When complemented with in vitro studies of embryo models (e.g., blastoids 16 , 17 , 18 ) such in vitro investigations will lead to the development of drug treatments that will rescue early pregnancy defects, including failure to implant, affecting more than 40% of in vivo implanting blastocysts.

Ultimately, female and male independence from the age-effects on our own gonadal function would be further enhanced through the ability to produce gametes in vitro. This production would be achieved by reprogramming somatic cells into iPSCs and differentiating them into gametes. In the next decade, such a process is likely to radically change patient perspectives about their fertility potential into advancing age, once they can be given the ability to produce autologous sperm or eggs at all ages in vitro. This gametic production would also revolutionize how fertility services are currently offered to infertile patients and would allow same-sex couples conception with shared genetic parenthood 19 . In the mouse, male and female gametes have already been successfully produced from stem cells 20 , and multiple laboratories around the world are currently trying to repeat this accomplishment in humans.

Ethical challenges

We believe that human embryology research and its ethical challenges will be increasingly seen as a driving force in addressing societal changes toward gender equality, and reduction in experimental use of animals and embryos. By establishing a more prominent dialogue between scientists, ethicists, funding/governmental agencies, and the public, we can build the medicine of tomorrow, including currently still largely unimaginable progress in fertility and pregnancy management, disease prevention and regenerative medicine. As previously noted, the most appropriate bodies addressing issues in reproductive research and clinical care are constantly challenged by scientific progress and adapting appropriate ethical frameworks to oversee the rapidly advancing field 3 .

As clinical perspectives become clear, ethical debates surrounding human embryology are likely to become centered around utilitarian arguments relative to health and diseases, rather than on cultural arguments, that are inherently diverse worldwide. Nevertheless, it is possible to foresee contradictory views on altering the genetic make-up of embryos, which would bring long-lasting genetic changes to future generations. The question will probably focus on whether there are clinical cases for which it would be ethical to modify preimplantation embryos considered as abnormal, with the intent of preventing pregnancy loss or diseases after birth. Whether such embryo transfers will become ethically acceptable is raised by two distinct clinical scenarios: the transfer of genetically-edited IVF embryos and the transfer of embryos produced by non-traditional means (e.g., issued from the fusion of gametes generated from genetically-edited stem cells). A recent opinion from the Ethics Committee of the ASRM under the heading “Ethics in embryo research ” concluded that such research with reproductive intent should only be undertaken after pre-clinical research demonstrates acceptable levels of safety and efficacy and with the intent of improving the health and/or well-being of offspring 21 . Although this opinion does not offer a precise framework, it points at the necessity to develop in vitro tests (e.g., human embryos cultures, embryo models) to assess the safety/efficacy of potential therapeutic approaches to treat, for example, monogenic inherited diseases.

Ethical considerations will always determine the pace of scientific, medical, and societal progress and we believe that these considerations should be based on a holistic evaluation of the risks and benefits. As such, it is important to remember that science is driven by an international community and must thus respect all ethical frameworks when establishing regulatory guidelines. We remain confident that the advances in human embryology over the next ten years will provide a tremendous window into our own origins and contribute to positive medical and societal changes.

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Acknowledgements

We like to thank Min Yang, Jean Marx Santel, Adam Souza, and Amir K. Brivanlou for data gathering and critical reading of the manuscript.

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Ali H. Brivanlou

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Nicolas Rivron

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Norbert Gleicher

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A.H.B., N.R., and N.G. all contributed to the manuscript.

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A.H.B. and N.G. are co-founders of OvaNova Inc. A.H.B. is a co-founder of Rumi Scientific Inc. N.R. is an inventor on a patent (EP2986711) and patent application (EP21151455.9) describing the mouse and human blastoid technologies.

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Brivanlou, A.H., Rivron, N. & Gleicher, N. How will our understanding of human development evolve over the next 10 years. Nat Commun 12 , 4614 (2021). https://doi.org/10.1038/s41467-021-24794-2

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Recent studies have narrowed down the probable period in prehistory when human speech likely originated. Research conducted by British archaeologist Steven Mithen indicates that early humans likely began to develop basic language skills approximately 1.6 million years ago, in regions situated in eastern or southern Africa.

“Humanity’s development of the ability to speak was without doubt the key which made much of subsequent human physical and cultural evolution possible. That’s why dating the emergence of the earliest forms of language is so important,” remarked Dr. Mithen, who serves as a professor of early prehistory at the University of Reading, to The Independent.

Prior to last month, the prevailing belief among experts in human evolution was that humans began speaking only around 200,000 years ago. However, Professor Mithen’s recent research, published in March, suggests that rudimentary human language dates back at least eight times further. His findings stem from a comprehensive analysis encompassing archaeological, paleo-anatomical, genetic, neurological, and linguistic evidence.

The amalgamation of this evidence suggests that the inception of language occurred within the broader context of human evolution and other advancements between two and 1.5 million years ago.

Notably, there was a notable acceleration in the enlargement of the human brain, particularly evident from around 2 million BC, with a more pronounced growth observed after 1.5 million BC. This increase in brain size was accompanied by a restructuring of the brain’s internal organization, including the emergence of the frontal lobe area specifically linked to language production and comprehension. Referred to by scientists as Broca’s area, it appears to have evolved from earlier structures associated with early human communication through hand and arm gestures.

Recent scientific findings propose a correlation between the emergence of Broca’s area and enhancements in working memory, a critical factor in constructing sentences. However, several other evolutionary advancements were also pivotal for the emergence of basic language. The development of a more sophisticated form of bipedalism around 1.8 million years ago, coupled with alterations in the human skull’s shape, likely initiated changes in the configuration and positioning of the vocal tract, thereby facilitating speech.

Furthermore, compelling evidence supporting the commencement of human speech around 1.6 million BC stems from the archaeological record. Unlike many other animal species, humans did not possess notable physical strength. To thrive, they had to compensate for this relative physical fragility.

Professor Mithen’s research also suggests a notable continuity between the earliest human languages and contemporary ones. He contends that certain aspects of the initial linguistic development, dating back 1.6 million years, persist in modern languages today. Notably, he proposes that early humans likely began with words that, through their sounds or length, directly described the objects they represented.

Moreover, future research may offer insights into reconstructing the probable organization and structure of those primitive languages. While the genesis of language is estimated to have occurred around 1.6 million years ago, it marked the inception of linguistic evolution rather than its culmination.

Over hundreds of thousands of years, language underwent gradual complexity, experiencing significant refinement with the advent of anatomically modern humans around 150,000 years ago.

Relevant articles: – The 1.6 million-year-old discovery that changes what we know about human evolution , Yahoo News UK – When did humans first start to speak? How language evolved in Africa , theconversation.com – What will humans look like in a million years? , bbcearth.com

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