Scientific American
EVOLUTION | OPINION
Race, Evolution and the Science of Human Origins
As museums reopen let’s introduce ourselves, and our children, to the original Black ancestors of all human beings
By Allison Hopper on July 5, 2021
After a year of lockdown, museums, libraries and bookstores across America are reopening. This cultural reawakening’s beginning coincided with both the Juneteenth holiday and the one-year anniversary of the one of the largest protests in American history against racial injustice. As bookstores reopen, many are organizing displays of children's books that celebrate Black history. What you won’t find in even the biggest collections of books is the story of the dark-skinned early people who launched human civilization.
The global scientific community overwhelmingly accepts that all living humans are of African descent. Most scientific articles about our African origins focus on genetics. The part of the story that is not widely shared is about the creation of human culture. We are all descended genetically, and also culturally, from dark-skinned ancestors. Early humans from the African continent are the ones who first invented tools; the use of fire; language; and religion. These dark skinned early people laid down the foundation for human culture. Considering the short life span of our early ancestors, these original innovators were probably also very young. No one who follows artistic trends will be surprised to learn that, from the beginning, human culture was essentially invented by teenagers. And by culture I don’t just mean the arts, I mean the whole shebang.
I want to unmask the lie that evolution denial is about religion and recognize that at its core, it is a form of white supremacy that perpetuates segregation and violence against Black bodies. Under the guise of “religious freedom,” the legalistic wing of creationists loudly insists that their point of view deserves equal time in the classroom. Science education in the U.S. is constantly on the defensive against antievolution activists who want biblical stories to be taught as fact. In fact, the first wave of legal fights against evolution was supported by the Klan in the 1920s. Ever since then, entrenched racism and the ban on teaching evolution in the schools have gone hand in hand. In his piece, What We Get Wrong About the Evolution Debate, Adam Shapiro argues that “the history of American controversies over evolution has long been entangled with the history of American educational racism.”
At the heart of white evangelical creationism is the mythology of an unbroken white lineage that stretches back to a light-skinned Adam and Eve. In literal interpretations of the Christian Bible, white skin was created in God's image. Dark skin has a different, more problematic origin. As the biblical story goes, the curse or mark of Cain for killing his brother was a darkening of his descendants' skin. Historically, many congregations in the U.S. pointed to this story of Cain as evidence that Black skin was created as a punishment.
The fantasy of a continuous line of white descendants segregates white heritage from Black bodies. In the real world, this mythology translates into lethal effects on people who are Black. Fundamentalist interpretations of the Bible are part of the “fake news” epidemic that feeds the racial divide in our country.
For too long, a vocal minority of creationists has hijacked children’s education, media and book publishing. Statistics on creationist beliefs in the US vary. Depending on the poll, up to 40 percent of percent of adults believe that humans have always existed in their present form (i.e., they believe in an unbroken human lineage stretching back to Adam and Eve).
We have seen some progress in the classroom. From 2007 to 2019, the percentage of teachers who present evolution without a creationist alternative grew dramatically, from only 51 percent to 67 percent. But it’s still not enough. My hope is that if we make the connection between creationism and racist ideology clearer, we will provide more ammunition to get science into the classroom—and into our culture at large.
It’s common knowledge that some school boards, especially in the South, have fought long and hard to keep evolution out of school textbooks. What you might not know is how the policing of educational content morphs into what might be called “self-censorship” within the children’s book industry as a whole. Scientific findings about human origins have been slow to trickle down into books written for young people. This major omission reflects the outsize effect that science-denying voices have on the books that find their ways not just into classrooms, but also into libraries, bookstores and children's homes. Fear of economic punishment within the publishing industry creates a self-perpetuating lack of teaching materials about evolution.
If you go on Amazon and look up “children’s books on evolution” you will find about 10–15 relevant titles. This is in contrast to the hundreds of children’s books on other scientific subjects such as chemistry, astronomy and other less controversial subjects. I found only one book on evolution for preschoolers, called Grandmother Fish. The author had to self-fund the book through Kickstarter.
On the other hand, there are hundreds of children’s books available on Amazon that focus on biblical origin stories. Science deniers are pumping money into a well-funded antievolution machine. In 2007, the creationists built their own Bible-themed museum and amusement park. What they understand is that to reach young children you need music, colorful characters and celebration.
In the Adam-and-Eve scenario, the Creator bestows both physical and cultural humanity on the first people. From the get-go Adam knows how to name the animals. No one has to invent language or figure out how to make tools. Science, of course, tells us otherwise. The process of natural selection shaped our bodies and capacities. Our humanity emerged over the millennia as creative ancient people figured out the crucial skills—from storytelling to cooking to rope making—that we now take for granted.
And yet, even in the current literature about human origins that we do have, the end point of evolution is often depicted as a white man carrying a spear. This image not only eliminates our African heritage but also erases women and children from the picture. Because evolution is foundational knowledge, we need the story to be told in many different ways, by many different voices.
As we move forward to undo systemic racism in every aspect of business, society, academia and life, let’s be sure to do so in science education as well. Embracing humanity’s dark-skinned ancestors with love and respect is key to changing our relationship to the past, and to creating racial equity in the present. These ancient people made the rest of us possible. Opening our hearts to them and embracing them as heroic, fully human and worthy of our respect is part of the process of healing from our racist history.
This is an opinion and analysis article; the views expressed by the author or authors are not necessarily those of Scientific American.
Allison Hopper is a filmmaker and designer with a master's degree in educational design from New York University. Early in her career, she worked on PBS documentaries. More recently, she's been creating content for young people on the topic of evolution. She has presented on evolution at the Big History Conference in Amsterdam and Chautauqua, among other places. Learn more about Allison and her projects at http://www.spiralzoom.com/. She recently completed a short animation titled Evolution and YOU!a>
Showing posts with label Scientific American. Show all posts
Showing posts with label Scientific American. Show all posts
Monday, July 5, 2021
Tuesday, October 6, 2020
This Washington Post article reminds me why another 4 years with President Fucktard Trump would be a disaster.
The Washington Post
Science
Scientific American backs Biden for its first presidential endorsement in 175 years
By Kim Bellware
September 15, 2020
The October issue of Scientific American will carry what has never been seen in the magazine’s pages in 175 years: a presidential endorsement.
In an urgent and impassioned editorial first published online Tuesday, the editorial board endorsed former vice president Joe Biden, the Democratic nominee, calling him the candidate “who is offering fact-based plans to protect our health, our economy and the environment.”
It was a striking move for the oldest continuously published magazine in the United States and one its editor in chief, Laura Helmuth, said was both carefully considered and entirely necessary. (Helmuth previously worked as The Washington Post’s science editor.)
Four years ago, the magazine flagged Donald Trump’s disdain for science as “frightening” but did not go so far as to endorse his rival, Hillary Clinton. This year, its editors came to a different conclusion.
“A 175-year tradition is not something you break lightly,” Helmuth told The Post on Tuesday. “We’d love to stay out of politics, but this president has been so anti-science that we can’t ignore it.”
The endorsement is one of several occasions during the president’s tenure when the scientific community has denounced President Trump’s beliefs and policies. The 2017 March for Science rallied the community to defend its institutions from budget cuts and undermining by Trump and his appointees. A growing movement to get scientists to run for political office emerged ahead of the 2018 midterm elections. Most recently in May, the medical journal the Lancet blasted Trump in an editorial for his “inconsistent and incoherent” coronavirus response.
Lancet editorial blasts Trump’s ‘inconsistent and incoherent’ coronavirus response
Scientific American’s 1,400-word editorial is as much an endorsement of Biden as it is a catalogue of Trump’s hostility to science throughout his term.
“The evidence and the science show that Donald Trump has badly damaged the U.S. and its people — because he rejects evidence and science,” the endorsement reads, citing his push to eliminate health rules from the Environmental Protection Agency, his rejection of stricter air pollution standards and his continued denial of climate change.
In a nod to Trump’s embrace of anti-science conspiracy theories, Scientific American editors compared the people each candidate turns to for expertise and insight. Biden’s panel of public health advisers include figures such as former U.S. Food and Drug Administration chief David Kessler and immunologist Rebecca Katz.
“It does not include physicians who believe in aliens and debunked virus therapies, one of whom Trump has called ‘very respected’ and “spectacular,’ ” the editors write.
Ultimately, it was Trump’s response to the novel coronavirus that created a new sense of urgency for Scientific American’s editors, Helmuth said.
“We’ve seen the consequences of this so tragically with the coronavirus pandemic. It will be 200,000 people who have died from the virus, and a lot of that is on his hands,” Helmuth said of Trump.
In a statement, Trump campaign spokesman Tim Murtaugh defended the president’s handling of the pandemic, writing, “President Trump has listened to the medical experts every step of the way to fight the coronavirus, and the experts agree that the restriction on travel from China saved thousands of American lives."
Despite the excoriation of the president for his anti-science stance, Helmuth stressed that the editors wanted their endorsement to be fact-based and evidence-backed — not partisan.
“We never used the world ‘Republican’ or ‘Democrat’; it’s strictly about these two people,” Helmuth said.
In such a politically fractured environment, Helmuth acknowledged that editors were concerned how an endorsement might read, and if it would undermine the public’s faith in scientific institutions like theirs.
Scientific American’s track record of not endorsing candidates is what could ultimately give its endorsement more weight, according to Paul Beck, a political scientist and professor emeritus at Ohio State University.
“An endorsement from an organization like that — that has been in the past above politics — would carry considerable weight with their audience,” Beck told The Post, calling the Scientific American endorsement “powerful.”
For an organization that has avoided political endorsements for so long to join the fray is unusual, Beck said — though when it comes to the 2020 race, he said, nothing surprises him.
“You have a truly anti-science president,” Beck said, “and the scientific community by and large has been appalled at what has come out of the president’s mouth and come out of Washington.”
Rancor between scientists and Trump allies threatens pandemic response as cases surge
The fractured news environments and hyper-partisanship of American politics have diminished the power of political endorsements compared with election cycles past, Beck said. Endorsements could still have an effect on undecided voters, whom he estimated at a small percentage of the electorate, in the realm of 10 percent or less.
When it comes to potential Trump voters, an endorsement from a respected outlet like Scientific American won’t move the die-hard supporters, he said, but it might sway Republicans or independents who already have doubts.
“You can imagine if I’m a subscriber to Scientific American, and a Republican, I might say, ‘Well, see, maybe I shouldn’t vote Republican this time around,’ ” Beck said.
Helmuth said that after careful consideration of what an endorsement would mean, the decision by Scientific American’s editorial board was ultimately unanimous.
“We cover the intersection of scientific issues that have political relevance,” she said, “but this is the first time we’ve said, ‘If you care about science and you’re a voter, there’s an obvious choice.’ ”
Science
Scientific American backs Biden for its first presidential endorsement in 175 years
By Kim Bellware
September 15, 2020
The October issue of Scientific American will carry what has never been seen in the magazine’s pages in 175 years: a presidential endorsement.
In an urgent and impassioned editorial first published online Tuesday, the editorial board endorsed former vice president Joe Biden, the Democratic nominee, calling him the candidate “who is offering fact-based plans to protect our health, our economy and the environment.”
It was a striking move for the oldest continuously published magazine in the United States and one its editor in chief, Laura Helmuth, said was both carefully considered and entirely necessary. (Helmuth previously worked as The Washington Post’s science editor.)
Four years ago, the magazine flagged Donald Trump’s disdain for science as “frightening” but did not go so far as to endorse his rival, Hillary Clinton. This year, its editors came to a different conclusion.
“A 175-year tradition is not something you break lightly,” Helmuth told The Post on Tuesday. “We’d love to stay out of politics, but this president has been so anti-science that we can’t ignore it.”
The endorsement is one of several occasions during the president’s tenure when the scientific community has denounced President Trump’s beliefs and policies. The 2017 March for Science rallied the community to defend its institutions from budget cuts and undermining by Trump and his appointees. A growing movement to get scientists to run for political office emerged ahead of the 2018 midterm elections. Most recently in May, the medical journal the Lancet blasted Trump in an editorial for his “inconsistent and incoherent” coronavirus response.
Lancet editorial blasts Trump’s ‘inconsistent and incoherent’ coronavirus response
Scientific American’s 1,400-word editorial is as much an endorsement of Biden as it is a catalogue of Trump’s hostility to science throughout his term.
“The evidence and the science show that Donald Trump has badly damaged the U.S. and its people — because he rejects evidence and science,” the endorsement reads, citing his push to eliminate health rules from the Environmental Protection Agency, his rejection of stricter air pollution standards and his continued denial of climate change.
In a nod to Trump’s embrace of anti-science conspiracy theories, Scientific American editors compared the people each candidate turns to for expertise and insight. Biden’s panel of public health advisers include figures such as former U.S. Food and Drug Administration chief David Kessler and immunologist Rebecca Katz.
“It does not include physicians who believe in aliens and debunked virus therapies, one of whom Trump has called ‘very respected’ and “spectacular,’ ” the editors write.
Ultimately, it was Trump’s response to the novel coronavirus that created a new sense of urgency for Scientific American’s editors, Helmuth said.
“We’ve seen the consequences of this so tragically with the coronavirus pandemic. It will be 200,000 people who have died from the virus, and a lot of that is on his hands,” Helmuth said of Trump.
In a statement, Trump campaign spokesman Tim Murtaugh defended the president’s handling of the pandemic, writing, “President Trump has listened to the medical experts every step of the way to fight the coronavirus, and the experts agree that the restriction on travel from China saved thousands of American lives."
Despite the excoriation of the president for his anti-science stance, Helmuth stressed that the editors wanted their endorsement to be fact-based and evidence-backed — not partisan.
“We never used the world ‘Republican’ or ‘Democrat’; it’s strictly about these two people,” Helmuth said.
In such a politically fractured environment, Helmuth acknowledged that editors were concerned how an endorsement might read, and if it would undermine the public’s faith in scientific institutions like theirs.
Scientific American’s track record of not endorsing candidates is what could ultimately give its endorsement more weight, according to Paul Beck, a political scientist and professor emeritus at Ohio State University.
“An endorsement from an organization like that — that has been in the past above politics — would carry considerable weight with their audience,” Beck told The Post, calling the Scientific American endorsement “powerful.”
For an organization that has avoided political endorsements for so long to join the fray is unusual, Beck said — though when it comes to the 2020 race, he said, nothing surprises him.
“You have a truly anti-science president,” Beck said, “and the scientific community by and large has been appalled at what has come out of the president’s mouth and come out of Washington.”
Rancor between scientists and Trump allies threatens pandemic response as cases surge
The fractured news environments and hyper-partisanship of American politics have diminished the power of political endorsements compared with election cycles past, Beck said. Endorsements could still have an effect on undecided voters, whom he estimated at a small percentage of the electorate, in the realm of 10 percent or less.
When it comes to potential Trump voters, an endorsement from a respected outlet like Scientific American won’t move the die-hard supporters, he said, but it might sway Republicans or independents who already have doubts.
“You can imagine if I’m a subscriber to Scientific American, and a Republican, I might say, ‘Well, see, maybe I shouldn’t vote Republican this time around,’ ” Beck said.
Helmuth said that after careful consideration of what an endorsement would mean, the decision by Scientific American’s editorial board was ultimately unanimous.
“We cover the intersection of scientific issues that have political relevance,” she said, “but this is the first time we’ve said, ‘If you care about science and you’re a voter, there’s an obvious choice.’ ”
Saturday, September 12, 2020
When I saw this I knew I had to put it here. "How Scientists Discovered the Staggering Complexity of Human Evolution"
Scientific American
EVOLUTION
How Scientists Discovered the Staggering Complexity of Human Evolution
Darwin would be delighted by the story his successors have revealed
By Kate Wong
Scientific American September 2020 Issue
In 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 at that time 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 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.
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.
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 may 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 the Cleveland Museum of Natural History and his team 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 a single 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 cheek bones 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—the recently discovered 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 may 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 may 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 may 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 actually 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 may 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 may 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 walked the earth—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 René 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 175 years 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.
FROM OUR ARCHIVES
Last Hominin Standing. Kate Wong; September 2018.
ABOUT THE AUTHOR
Kate Wong
Kate Wong is a senior editor for evolution and ecology at Scientific American.
Recent Articles
How Birds Evolved Their Incredible Diversity
Stone Age String Strengthens Case for Neandertal Smarts
Is This Indonesian Cave Painting the Earliest Portrayal of a Mythical Story?
EVOLUTION
How Scientists Discovered the Staggering Complexity of Human Evolution
Darwin would be delighted by the story his successors have revealed
By Kate Wong
Scientific American September 2020 Issue
In 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 at that time 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 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.
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.
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 may 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 the Cleveland Museum of Natural History and his team 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 a single 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 cheek bones 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—the recently discovered 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 may 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 may 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 may 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 actually 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 may 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 may 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 walked the earth—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 René 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 175 years 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.
FROM OUR ARCHIVES
Last Hominin Standing. Kate Wong; September 2018.
ABOUT THE AUTHOR
Kate Wong
Kate Wong is a senior editor for evolution and ecology at Scientific American.
Recent Articles
How Birds Evolved Their Incredible Diversity
Stone Age String Strengthens Case for Neandertal Smarts
Is This Indonesian Cave Painting the Earliest Portrayal of a Mythical Story?
One of the reason why millions of American morons prefer magic instead of science: The biology teachers are uneducated morons. It's a ridiculous disgraceful problem but it used to be much worse than it is now.
Scientific American
EVOLUTION
OPINION
Evolution Education in the U.S. Is Getting Better
The percentage of public school bio teachers who present it as the broad consensus view among scientists—without presenting the creationist “alternative”—has increased markedly since 2007.
By Glenn Branch and Ann Reid
September 12, 2020
Woo-hoo, d’oh, or meh? Which of these Simpsonian reactions is appropriate to the fact, revealed by a 2019 survey conducted by researchers at Penn State University and the National Center for Science Education (NCSE), that about two in three—67 percent—of public high school biology teachers are presenting evolution forthrightly, emphasizing the broad scientific consensus on evolution while not giving any credence to creationism? Only in the context of the long and contentious history of evolution education in the United States is it clear what the most plausible answer is.
American teachers have not always been afforded the luxury of teaching evolution forthrightly. John Thomas Scopes, for example, was famously prosecuted for violating Tennessee’s ban on teaching evolution in 1925. Although his conviction was subsequently overturned, a national survey of high school biology teachers conducted in 1939–1940 revealed that only about half were teaching evolution as a central principle of biology. And bans on teaching evolution remained in place in Arkansas, Mississippi and Tennessee until 1970.
New obstacles then emerged, particularly requirements to teach various forms of creationism as alternatives to evolution. As recently as 15 years ago, in Dover, Pennsylvania, the local school board attempted to require its high school biology teachers to read a statement to their ninth-grade students describing “Darwin’s theory of evolution” as “not a fact,” and commending “intelligent design”—then a trendy slogan for creationism—to their attention as a scientifically credible alternative. The teachers, to their credit, unanimously refused to comply.
But their refusal, together with the controversy surrounding the related trial over the constitutionality of the board’s actions, Kitzmiller v. Dover, intrigued two parents a hundred miles to the northwest, in State College, Pa. Michael Berkman and Eric Plutzer were not just any concerned parents, though: they were political scientists at Penn State with a particular interest in education policy. What—they wondered—are high school biology teachers teaching about evolution, and what factors influence their teaching practices?
To satisfy their curiosity, Berkman and Plutzer conducted the first modern national survey of high school biology teachers in 2007. The results were dire. Only a slight majority, 51 percent, reported that they emphasized the broad scientific consensus on evolution while not giving any credence to creationism, as if to suggest no progress in the 67 years since the less rigorous survey of 1939–1940. That’s why the results of the 2019 survey—a collaboration between Plutzer and the NCSE—are so encouraging.
Between 2007 and 2019, there definitely was progress: from 51 percent of high school biology teachers reporting emphasizing evolution and not creationism in 2007 to 67 percent in 2019. It was matched by a drop from 23 to 12 percent of teachers who offer mixed messages by endorsing both evolution and creationism as a valid scientific alternative to evolution, from 18 to 15 percent of teachers who endorse neither evolution nor creationism, and from 8.6 to 5.6 percent of teachers who endorse creationism while not endorsing evolution.
What accounts for the improvement? Did intelligent design’s crushing defeat in the Kitzmiller trial make the difference? Probably not. Science teachers are guided not by case law but by state science standards, which specify what students in the state’s public schools are expected to learn. Standards thus influence the content of textbooks, statewide testing, and coursework for pre-service and in-service teachers. Importantly, they also provide a shield for teachers facing misguided community pressure over socially contentious topics like evolution.
The results of the 2019 survey suggest that a concerted effort to improve state science standards helped to improve evolution education. The Next Generation Science Standards (NGSS), which debuted in 2013, include “Biological Evolution: Unity and Diversity” as a disciplinary core idea of the life sciences at the middle and high school levels. By now, 20 states (plus the District of Columbia) have adopted the NGSS, and a further 24 states have adopted standards based on the same evolution-friendly framework on which the NGSS are based.
Were states that adopted the NGSS especially hospitable to the teaching of evolution? Not really: in 2007, their teachers were less likely to endorse evolution and not creationism than the national average. By 2019, they were more likely. While a variety of explanations are possible, teachers in NGSS states reported having taken more pre-service and in-service coursework in evolution than their colleagues elsewhere, suggesting that the increased expectations impelled both novice and veteran teachers to upgrade their content knowledge of evolution.
Despite the encouraging trend over a mere dozen years, there is still reason for concern: after all, more than one in six high school biology teachers, 17.6 percent, are still presenting creationism as a scientifically credible alternative to evolution. And almost as many high school biology teachers, 15 percent, are still failing to emphasize the broad scientific consensus on evolution, despite its general prevalence in state science standards and despite encouragement from professional organizations. D’oh!
With 13,500-odd local school districts having primary responsibility for curriculum and instruction, changes to science education are inevitably going to be slow, scattered and incremental. Still, with the aid of uncounted scientists, educators, policymakers, administrators and concerned citizens in general (and perhaps even a certain episode of The Simpsons), clear and convincing improvements for evolution education were demonstrably attained in just a dozen years. It is a victory worth not only celebrating—woo-hoo!—but also enlarging upon.
Glenn Branch and Ann Reid
Glenn Branch is deputy director and Ann Reid is executive director of the National Center for Science Education, a nonprofit organization that supports the accurate teaching of evolution and climate change.
EVOLUTION
OPINION
Evolution Education in the U.S. Is Getting Better
The percentage of public school bio teachers who present it as the broad consensus view among scientists—without presenting the creationist “alternative”—has increased markedly since 2007.
By Glenn Branch and Ann Reid
September 12, 2020
Woo-hoo, d’oh, or meh? Which of these Simpsonian reactions is appropriate to the fact, revealed by a 2019 survey conducted by researchers at Penn State University and the National Center for Science Education (NCSE), that about two in three—67 percent—of public high school biology teachers are presenting evolution forthrightly, emphasizing the broad scientific consensus on evolution while not giving any credence to creationism? Only in the context of the long and contentious history of evolution education in the United States is it clear what the most plausible answer is.
American teachers have not always been afforded the luxury of teaching evolution forthrightly. John Thomas Scopes, for example, was famously prosecuted for violating Tennessee’s ban on teaching evolution in 1925. Although his conviction was subsequently overturned, a national survey of high school biology teachers conducted in 1939–1940 revealed that only about half were teaching evolution as a central principle of biology. And bans on teaching evolution remained in place in Arkansas, Mississippi and Tennessee until 1970.
New obstacles then emerged, particularly requirements to teach various forms of creationism as alternatives to evolution. As recently as 15 years ago, in Dover, Pennsylvania, the local school board attempted to require its high school biology teachers to read a statement to their ninth-grade students describing “Darwin’s theory of evolution” as “not a fact,” and commending “intelligent design”—then a trendy slogan for creationism—to their attention as a scientifically credible alternative. The teachers, to their credit, unanimously refused to comply.
But their refusal, together with the controversy surrounding the related trial over the constitutionality of the board’s actions, Kitzmiller v. Dover, intrigued two parents a hundred miles to the northwest, in State College, Pa. Michael Berkman and Eric Plutzer were not just any concerned parents, though: they were political scientists at Penn State with a particular interest in education policy. What—they wondered—are high school biology teachers teaching about evolution, and what factors influence their teaching practices?
To satisfy their curiosity, Berkman and Plutzer conducted the first modern national survey of high school biology teachers in 2007. The results were dire. Only a slight majority, 51 percent, reported that they emphasized the broad scientific consensus on evolution while not giving any credence to creationism, as if to suggest no progress in the 67 years since the less rigorous survey of 1939–1940. That’s why the results of the 2019 survey—a collaboration between Plutzer and the NCSE—are so encouraging.
Between 2007 and 2019, there definitely was progress: from 51 percent of high school biology teachers reporting emphasizing evolution and not creationism in 2007 to 67 percent in 2019. It was matched by a drop from 23 to 12 percent of teachers who offer mixed messages by endorsing both evolution and creationism as a valid scientific alternative to evolution, from 18 to 15 percent of teachers who endorse neither evolution nor creationism, and from 8.6 to 5.6 percent of teachers who endorse creationism while not endorsing evolution.
What accounts for the improvement? Did intelligent design’s crushing defeat in the Kitzmiller trial make the difference? Probably not. Science teachers are guided not by case law but by state science standards, which specify what students in the state’s public schools are expected to learn. Standards thus influence the content of textbooks, statewide testing, and coursework for pre-service and in-service teachers. Importantly, they also provide a shield for teachers facing misguided community pressure over socially contentious topics like evolution.
The results of the 2019 survey suggest that a concerted effort to improve state science standards helped to improve evolution education. The Next Generation Science Standards (NGSS), which debuted in 2013, include “Biological Evolution: Unity and Diversity” as a disciplinary core idea of the life sciences at the middle and high school levels. By now, 20 states (plus the District of Columbia) have adopted the NGSS, and a further 24 states have adopted standards based on the same evolution-friendly framework on which the NGSS are based.
Were states that adopted the NGSS especially hospitable to the teaching of evolution? Not really: in 2007, their teachers were less likely to endorse evolution and not creationism than the national average. By 2019, they were more likely. While a variety of explanations are possible, teachers in NGSS states reported having taken more pre-service and in-service coursework in evolution than their colleagues elsewhere, suggesting that the increased expectations impelled both novice and veteran teachers to upgrade their content knowledge of evolution.
Despite the encouraging trend over a mere dozen years, there is still reason for concern: after all, more than one in six high school biology teachers, 17.6 percent, are still presenting creationism as a scientifically credible alternative to evolution. And almost as many high school biology teachers, 15 percent, are still failing to emphasize the broad scientific consensus on evolution, despite its general prevalence in state science standards and despite encouragement from professional organizations. D’oh!
With 13,500-odd local school districts having primary responsibility for curriculum and instruction, changes to science education are inevitably going to be slow, scattered and incremental. Still, with the aid of uncounted scientists, educators, policymakers, administrators and concerned citizens in general (and perhaps even a certain episode of The Simpsons), clear and convincing improvements for evolution education were demonstrably attained in just a dozen years. It is a victory worth not only celebrating—woo-hoo!—but also enlarging upon.
Glenn Branch and Ann Reid
Glenn Branch is deputy director and Ann Reid is executive director of the National Center for Science Education, a nonprofit organization that supports the accurate teaching of evolution and climate change.
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