Monday, August 21, 2017

Is Science Broken?

Or is it self-correcting?

Lisa Larson-Walker
Two years ago this month, news of the replication crisis reached the front page of the New York Times. “Psychology’s Fears Confirmed: Rechecked Studies Don’t Hold Up,” read the A1 headline on the morning of Aug. 28, 2015. The journal Science had just published a landmark effort to reproduce the findings of 100 recent peer-reviewed psychology experiments, and just 39 of those replications succeeded. This dispiriting result, the Times reported, “confirmed the worst fears of scientists who have long worried that the field needed a strong correction.”
Daniel Engber is a columnist for Slate
In a matter of hours, news of this massive scientific failure drifted into right-wing media. “So many people in the country have lost faith in so many institutions they used to trust,” Rush Limbaugh told his 13 million listenersin a bloviating monologue on the mendacity of the elites and the rise of Donald Trump. Now, the radio host explained, the American people had cause to turn on science, too. “What you can assume here, safely so, is that the vast majority of what you hear—if you hear, ‘from the journal Science,’ ‘from the journal [sic] Psychology Today’—it’s all bogus,” he said. “What has been exposed here is that science is no different than anything else in politics. It is totally determined by money. Scientific results can be purchased.”
With that, another of scientists’ biggest fears was confirmed: that any discovery of major problems in their field would end up being used against them. They’d worried that front-page coverage of the “replication crisis” would give Limbaugh types ammunition to knock them off their pedestal, and a fresh excuse to flush their carefully collected data into the sea of politics and ideology. Now it looked as though that fear, too, had been borne out. “The game is rigged,” Limbaugh concluded that day in 2015. “Everything’s been so corrupted, science especially, by politics.”
Could Limbaugh’s rant be taken as a cautionary tale for science journalism—an example of what happens when reporters catastrophize the replication crisis? A new book, The Oxford Handbook of the Science of Science Communication, lays out this case. News stories about problematic research often serve as chum for anti-science trolls, argue professors Joe Hilgard of Illinois State University and Kathleen Hall Jamieson of the University of Pennsylvania in a thoughtful chapter titled “Science as ‘Broken’ Versus Science as ‘Self-Correcting.’ ” The risk is most acute when journalists recklessly suggest that science, as a whole, has somehow gone off the rails. When they employ a “science is broken” frame, they end up causing “reputational harm to science” and contributing to a dangerous and misleading “news climate” that can be “mined by those interested in attacking scientific findings they consider ideologically uncongenial.”
According to Hilgard and Jamieson, science isn’t really broken and reporters oughtn’t say it is. They argue that scandals in the field show the ways that science works: Whenever there’s a problem, it self-corrects. That’s the frame they recommend to journalists, “science is self-correcting,” and the deeper truth they’d like to see expressed. When it comes to science, they believe, a crisis is a sign of strength.
Let me frame my thoughts on this as clearly as I can: I think Hilgard and Jamieson are wrong. Science is broken, at least by any useful definition of the word. Self-correction doesn’t always happen, and science journalists mustn’t be afraid to spell that out.
I’ll admit this conversation strikes a nerve as I’ve been working in the “broken science” frame for a long time now. In my year and a half on the replication beat for Slate, the phrase science is broken has appeared in the headlines of two of my stories. Another headline claimed that “cancer research is broken,” while a fourth announced, with reference to psychology, that “everything is crumbling.” I could say that reporters rarely write their own headlines—indeed, those phrases originated with my editors—and that I don’t believe I’ve ever put the B-word in the body of a replication piece. But I stand behind the framing nonetheless.
In the last few years we’ve learned that science sometimes fails to work the way it should. Suggesting it might be “broken” is not the same as saying it’s in a state of utter, irreversible decrepitude—that every published finding is a lie, or that every field of research is in crisis. Rather, it suggests a dawning sense that things have gotten wonky in a widespread way. It says our vaunted engine of discovery is sputtering and that it’s time we brought it in for repairs.
It was Robert Hooke, four centuries ago, who first described the scientific method in this way, as a sort of engine for “directing the mind in the search after Philosophical Truths.” By the 1700s, scientists had gained a bit more modesty; they admitted that their machine sometimes got things wrong. A new idea took hold of science as a self-correcting enterprise that converges, sometimes sloppily, on the truth. One natural philosopher likened research to the act of doing long division: With each step, the remainder shrinks a little more, and the field naturally inches ever closer to the correct answer. This theory of the scientific method—as less an engine than a self-driving car that glides toward knowledge—was most famously asserted by the philosopher Charles Sanders Peirce. “This marvelous, self-correcting property of Reason … belongs to every sort of science,” he said in 1898.
The marvelous property has since been wielded, on occasion, as a magic wand to wave away egregious missteps. Whenever a researcher is outed as a fraud, it’s inevitable that some science poobah will describe the mere fact of the miscreant’s discovery as a victory for “self-correction.” Here’s how Hilgard and Jamieson deploy the frame in reference to the 2014 case of a Japanese stem-cell researcher whose paper was retracted after she’d been found guilty of manipulating data: “If critique and self-correction are hallmarks of the scientific enterprise, then instances in which scientists detect and address flaws constitute evidence of success, not failure, because they demonstrate the underlying protective mechanisms of science at work.”
In the stem-cell case, self-correcting science did appear to work as advertised: Problems in the paper were discovered by attentive colleagues shortly after it appeared in print. But the recent history of science fraud suggests that many more examples come to light not quickly and not via any standard self-corrective mechanism—e.g., peer review or unsuccessful replications—but rather at a long delay and through the more conventional means of whistleblowing. That’s how Diedrik Stapel, a notorious fabulist with 58 retracted papers in social psychology, was discovered in 2011. The fact that Stapel’s brazen fraud had not been caught (or self-corrected) earlier made his case a seminal event in the current replication crisis. Why had no one noticed, in strictly scientific terms, all the false effects that he’d slipped into the literature?
Isolated fraud has never been the substance of the crisis, though. In the years since Stapelgate, piles of perfectly ethical research papers have been perched on precarious data. It turned out that industry-standard methods of designing, analyzing, and reporting on experiments could yield seemingly impossible results—the existence of ESP, for example, or an ability to time-travel. By the time Rush Limbaugh started yammering about “bogus science” in the summer of 2015, psychologists, doctors, and researchers in several other disciplines already had the inkling that a startling proportion of their fields’ discoveries could be little more than statistical noise.
In fact, the week before the New York Times put the replication crisis on A1, science journalist Christie Aschwanden laid out these facts in great detail in a wonderful article and interactive for FiveThirtyEight. Her piece runs through the many biases, errors, and inefficiencies of modern scientific practice that allow false findings to infiltrate the literature. Researchers can hack their way to spurious conclusions, and they’re incentivized to hide negative results. Journal editors ignore replication failures, and they’re often slow to fix mistakes.
Aschwanden’s piece could be thought of as a thorough brief for the argument that science is, indeed, a shit show—that its self-corrective mechanisms have fallen into disrepair. Yet her reporting reaches the opposite conclusion. “Science isn’t broken, nor is it untrustworthy,” she writes. “It’s just more difficult than most of us realize.” The problem, says Aschwanden, is that we expect too much of science; we act like it’s an engine for discovery, when it’s just a means of moving, herky-jerky, down the long and curvy road to truth. If science looks to be a mess, she says, that’s because it’s messy work. It’s “a process of becoming less wrong over time,” she explained in a subsequent, equally optimistic piece with the headline, “Failure Is Moving Science Forward: The replication crisis is a sign that science is working.”
I haven’t seen a better set of write-ups in the “science is self-correcting” mode. (Aschwanden’s original piece richly deserves the multiple awards it has received.) Even so, this framing has always struck me as bizarre. It’s as if we’d noticed that the engine in our car was on fire, and then concluded that the vehicle must be running fine, because otherwise how would we have ever seen the smoke billowing out from underneath the hood? To put it another way: If the replication crisis is a sign that science isn’t broken, then what does “broken” even mean?
It may be true that, eventually, science self-corrects. (At the very least it’s impossible to falsify that claim.) But the more relevant question is, how quickly does science self-correct? Are bad ideas and wrong results stamped out within a year or two, or do they last for generations? How many hours must we squander in the lab in pursuit of empty theories? How many research grants are wasted? What proportion of our scientists’ careers will be frittered away on the trail of nothing much at all?
It’s tempting to assume that self-correction is a force of nature and that every faulty fact will molder and decay. But the replication crisis shows there is no half-life for our bungling. In practice, we must always act to fix mistakes—and that action often gets delayed beyond all reason. That’s what it means to say that science is “broken”: It’s not that all of science is a sham but that it’s not self-correcting fast enough.
For example, it's been known for half a century that psychology studies tend to be too small. In a 1962 paper, statistician Jacob Cohen showed that psychologists rarely used as many subjects as they should, and that they were “non-rational” in their approach to choosing sample sizes. All this underpowered work was therefore “wasteful of research effort,” he said. His critique would be repeated and expanded many times after, including in famous work by luminaries of the field. Yet nothing changed for decades; the culture and convention never budged. A meta-analysis published last fall concluded that, up through 2011, studies in psychology were exactly as weak, statistically, as they’d been in 1960. “Power has not improved despite repeated demonstrations of the necessity of increasing power,” the authors wrote.
Anecdotally, it seems there’s been a bit of movement in the last few years—sample sizes may at last be inching up. (Several other vital fixes have also begun to spread, including study pre-registration and data sharing.) But the change in practice—if in fact there’s been a change in practice—only came after researchers spent more than 50 years mindlessly repeating the same mistakes. It took Diedrik Stapel’s fraud, and a paper “proving” ESP, and the growing sense that science is in crisis to make them “self-correct.” First the scientists had to figure out that Cohen’s quibble wasn’t just some technicality, but rather that it pointed to a deep dysfunction in their field. That is to say, they had to grapple with the naked fact that psychology was broken.
Even now, efforts to self-correct psychology have been slow and controversial. Not everyone agrees the field needs substantial fixing, especially among the older tenured generation. That’s why it worries me when I hear scientists say that stories on the replication crisis should be framed a certain way. Conservatives in science naturally prefer the “self-correcting” frame, since it implies protection of the status quo, and greater deference to authority. When we talk about brokenness, we make it harder to pretend that everything’s going to be OK.

Thursday, August 10, 2017

Archaeologists Find Destruction Left by Babylonian Conquest of Jerusalem

Ruth Schuster7/26/2017
A bizarrely uneven but unmistakable destruction layer dating from the Babylonian conquest of Jerusalem in 586 B.C.E. has been found by archaeologists digging in the City of David, at the foot of the Old City of Jerusalem. The layer was found inside houses that had been built outside the city walls, indicating that sixth-century B.C.E. Jerusalem extended beyond the fortifications.
The layer was found inside a number of stone buildings on the lower slopes of the City of David, basically just downhill from the entrance to Warren's Shaft, Dr. Joe Uziel, excavation director for the Israel Antiquities Authority, told Haaretz.
"Jerusalem is known for two major destructions in its early history. One was in 586 B.C.E., when the Babylonians destroyed the city. The other was in the year 70 C.E., when the Romans destroyed Jerusalem," Uziel says.
Much evidence indicates that the destruction layer, with ash and collapsed layers of stone, dates to the Babylonians some 2,600 years ago, rather than to the Romans 2,000 years ago. A key piece is iconic rosette shapes stamped onto the handles of pottery storage jars: dozens of shattered jars were found at the site. That provides a very tight range of dates. (It also attests possibly to the violence of the time.)
"Rosette handles date to a very short time period, right up to the Babylonian destruction in 586 B.C.E.," Uziel says, adding, "We find rosette handle stamps whenever we find Babylonian destruction levels in the early sixth century B.C.E."
The rosette-decorated jar handles were a brief chapter in a centuries-long Judahite bureaucratic system in the Iron Age.
The earliest known jar-handle stamps date to the time of King Hezekiah in the late eighth century B.C.E. These stamps included the ancient Hebrew letters lamed, mem, lamed and kaf, and the name of one of four cities associated with Judah. They have become known as "LMLK seals" ("to the king" or "for the king").
Jug handles with the rosette seal used by the administrative system at the end of the Judean Kingdom in the seventh century B.C.E.. Eliyahu Yanai, Courtesy of the City of David Archive
"Many link the LMLK handles to preparations prior to the arrival of the Assyrian army, which managed to conquer Judah in 701 B.C.E., but not Jerusalem. LMLK handles began to appear right before that," Uziel explains.
In any case, after the Assyrian onslaught, the LMLK handles disappeared, following which rosette handles began to show up, replacing the LMLK system – until the Babylonian destruction. And now a bunch have been found in this destruction layer in Jerusalem. (After the Babylonian destruction, other stamp seals began to appear on jar handles in the place of the rosettes.)
By the way, the jars had been used to store both liquids and grains, say the archaeologists, given that modern techniques enable analysis of a jar's ancient content, if any residue is left.
Ivory statuette of naked woman
The archaeologists also found a small ivory statue of a woman, an extremely rare discovery. The figure is naked and her haircut or wig is Egyptian in style, they say, adding that the quality of the workmanship is high.
Intriguingly, the destruction layer the archaeologists found varies in thickness, from as much as a meter in what seems to have been a storage room for jars, to practically indiscernible. Why would the signs of mayhem be so glaring in some areas, and almost nonexistent in others?
"We think the Babylonians didn’t burn each and every building." Uziel says. "The process may have been to destroy certain points they didn't have to destroy every single building in order to destroy Jerusalem."
In the excavations – concentrated on the eastern slope of the City of David – structures dating to more than 2,600 years ago have been unearthed after having been covered over by collapsed layers of stone.
Within the destruction layer, the excavators found charred wood, grape seeds, pottery, fish scales and bones as well. Carbon-14 dating with the help of the Weizmann Institute is in process.
It bears adding that the adoption of carbon-dating in Jerusalem archaeology has been glacial, though people have been excavating the city for a century and more and the technology is hardly new. Finally, though, it is being used. It's a process, Uziel admits, adding, "In recent years we have made large effort, the Israel Antiquities Authority and the universities, to bring Jerusalem to the methods of 21st century archaeology."
We have still not found the missing link between us and apes.

[[For those who think that evolution has finally got it all rapped up.]]

The average missing person's inquiry begins with a few vital facts. Investigators often know when and where the missing party was last seen. They might have photographs that tell them what the missing person looks like, and they usually have a name to put to that face.
Now imagine beginning a similar sort of inquiry with none of this information.
About 150 years ago, when Charles Darwin published his theory of evolution through natural selection, scientists began to accept that humans – for all our sophisticated behaviour – belong to the same family tree as all other animals.
The idea led to two inescapable conclusions. First, our species is not an only child. Somewhere out there in the natural world, there is at least one species of animal that is more closely related to humans than any other – what biologists would come to call humanity's "sister species".
Secondly, and as importantly, our species has a long-lost parent. It stands to reason that if humanity has one or more sisters, then these siblings must have shared the same parent species at some point in prehistory. Evolutionary biologists call this species the "last common ancestor" (LCA). Most people know it by a non-scientific name: the "missing link".
Scientists have been on the trail of the LCA for decades, and they still have not found it. But many are convinced that they have established enough information to make the hunt a lot easier. They think they know roughly when and where the LCA lived. They even have a reasonable idea of what it looked like and how it behaved.
A chimpanzee (Pan troglodytes) (Credit: Anup Shah/
A chimpanzee (Pan troglodytes) (Credit: Anup Shah/
Even before Darwin formalised the idea of evolution through natural selection, it was clear that humans were primates – although earlier scientists did not think this categorisation had any evolutionary implications.
Apes in general represented evolutionary staging posts on the road to humanity
Darwin himself was initially reluctant to directly address human evolution. He barely mentioned the subject in his famous book On the Origin of Species.
Darwin's colleague, Thomas Henry Huxley, was perhaps the first to try to identify humanity's roots using well-reasoned evolutionary thinking. In his 1863 book Evidence as to Man's Place in Nature, Huxley said it was "quite certain", anatomically speaking, that humans are most similar to gorillas and chimpanzees. One of these two must be humanity's sister species, although Huxley was not sure which.
Huxley's ideas had a significant impact on 19th and early 20th Century evolutionary biologists. Many enthusiastically embraced the idea that chimps or gorillas – or even both – were our sister species. But they went further. To these biologists, it seemed that apes in general represented evolutionary staging posts on the road to humanity.
Gibbons are more distantly related to us (Credit: Anna Yu/Alamy)
Gibbons are more distantly related to us (Credit: Anna Yu/Alamy)
"Lesser" apes like the gibbons offered a window into the anatomy of our earliest ape ancestors. Meanwhile the "great" apes – gorillas, chimpanzees and orangutans – showed the anatomical features our ancestors possessed at the moment they split away from the other apes and began to develop a uniquely human appearance. Gorillas and chimps were not simply our sister species: they were also a lot like the LCA.
"The post-Darwinian 'paradigm' adopted living chimpanzees as stand-ins for the LCA," says Tim White, a palaeoanthropologist at the University of California, Berkeley.
This led to some very particular ideas about how the LCA looked and behaved. Primates in general (particularly monkeys) are often relatively small-bodied, and they scamper around in forest canopies by running along branches. But apes are unusual primates. Most have big bodies with extraordinarily long arms. They often get around by swinging below branches rather than running along the top of them – a form of locomotion called "brachiation".
According to many of these early researchers, the LCA was a large-bodied, long-armed, brachiating ape.
Are chimpanzees our closest relatives? (Credit: Florian Möllers/
Are chimpanzees (Pan troglodytes) our closest relatives? (Credit: Florian Möllers/
By the late 1960s, researchers were fleshing out the LCA even further. An anthropologist called Sherwood Washburn pointed out that chimpanzees, and particularly gorillas, actually spend significant amounts of time moving around on all fours on the forest floor.
Humans just are not particularly "evolved"
Both apes use their arms in an idiosyncratic way when they walk: they flex their fingers so that their weight bears down on the knuckles. To Washburn it made sense that the LCA "knuckle-walked" too. The behaviour could even be seen as a stepping-stone on the way to walking upright on two legs, he wrote.
But it would be wrong to think that everyone was on board with these ideas of a brachiating, knuckle-walking, chimp-like LCA. In fact, almost from the moment that Huxley first put pen to paper, a minority of scientists were arguing that the earliest human ancestors – and the LCA – was decidedly not chimp-like.
For instance, just a decade after Huxley's book, biologist St George Mivart argued that humans shared many features in common with monkeys or even lemurs. Meanwhile, from 1918 onwards an anatomist called Frederic Wood Jones argued that humans had a lot more in common with tarsiersthan with chimpanzees or gorillas.
Lemurs, tarsiers and monkeys are primates, but they have been evolving independently of the apes for tens of millions of years. How could anyone argue that humans are closely related to these groups? There is a simple and astonishing explanation, wrote anatomist William Straus in the 1940s. Humans just are not particularly "evolved".
A mountain gorilla (Gorilla beringei beringei) (Credit: Ole Jorgen Liodden/
A mountain gorilla (Gorilla beringei beringei) (Credit: Ole Jorgen Liodden/
It might seem absurd to argue that our highly developed brain is anything other than an example of primate evolution pushed to the extreme. But human arms, hands, legs and feet are not as highly specialised as we might assume.
"In these characters man finds his counterparts not in anthropoid apes [gorillas, chimpanzees and orangutans] but in animals that are clearly regarded… as more primitive," wrote Straus.
The more ancient the divergence between species, the more time those species have had to accumulate their own molecular differences
What Straus and a few others were really getting at is that humans show none of the specialised features that allow other apes to swing through the trees. It made sense to at least consider the possibility that humans split apart from other primates before the apes evolved brachiation, or knuckle-walking for that matter.
Straus could not say exactly which species should be recognised as our sister. But the LCA could well have been a relatively small-bodied primate that ran along branches rather than swinging beneath them.
This disagreement continued for several more decades, says Nathan Young at the University of California in San Francisco. In fact, even into the 1980s it was not clear from anatomical features alone exactly where humans slotted into the primate evolutionary tree.
Then, just a decade later, this uncertainty vanished. By the late 1990s, almost all evolutionary biologists were willing to accept that chimpanzees, and their close relatives the bonobos, together form humanity's sister species.
To understand this turning point in the story, we have to skip back a few decades and look at what was going on in a completely different branch of science.
Australopithecus afarensis lived around 3 million years ago (Credit: Lanmas/Alamy)
Australopithecus afarensis lived around 3 million years ago (Credit: Lanmas/Alamy)
In 1960, Nobel-Prize-winning chemist Linus Pauling accepted an invitation to write a paper in a special scientific volume dedicated to Albert Szent-Györgyi, the discoverer of vitamin C. Working with his colleague, Emile Zuckerkandl, Pauling developed a truly revolutionary idea: the molecular clock.
Ramapithecus was discovered in Pakistan and dated to about 14-16 million years old
"It was a revival of an idea proposed by bacteriologist George Nuttall in 1904, that if you compared blood serum you could get a sense for the evolutionary closeness of species," says Jeffrey Schwartz, a physical anthropologist at the University of Pittsburgh in Pennsylvania, US. "Their paper articulated the assumption that molecules are constantly changing, and the more ancient the divergence between species, the more time those species have had to accumulate their own molecular differences."
Pauling and Zuckerkandl used this concept – that some molecules accumulate tiny changes at a steady rate – to analyse proteins in human and gorilla blood. From the number of differences between the two sets of molecules, and an estimate of the rate that those differences accumulate, the researchers calculated that humans and gorillas had last shared a common ancestor roughly 11 million years ago.
Anthropologists were unimpressed. Only fossils could tell us when common ancestors lived, they argued. Many reportedly described Pauling and Zuckerkandl's concept as crazy. But the molecular scientists stuck at their work and, a few decades later, they won over the sceptics – due in no small part to new fossil finds.
All manner of fossil primates, including apes, had come to light by the 1960s. One of them, an ape called Ramapithecus or sometimes Sivapithecus, had begun to look a lot like a direct human ancestor.
A jawbone of Ramapithecus (Credit: Granger Historical Picture Archive/Alamy)
A jawbone of Ramapithecus (Credit: Granger Historical Picture Archive/Alamy)
"Ramapithecus was discovered in Pakistan and dated to about 14-16 million years old," says Schwartz. "It had thick enamel, which is a feature we see in humans and their immediate ancestors." In contrast, chimps and gorillas have a thinner coating of enamel on their teeth.
The molecular people said 'See? We were right all along!'
By 1964, palaeoanthropologists were even prepared to speculate that Ramapithecus walked on the ground like a human and used tools to prepare its food. And if the 14-million-year-old Ramapithecus really was a human ancestor, gorillas and humans cannot possibly have shared a common ancestor just 11 million years ago, as Pauling and Zuckerkandl were suggesting.
But these conclusions about Ramapithecus came almost exclusively from a study of the ape's teeth, which were more or less the only parts of the ancient ape that had been unearthed by the 1960s. In the early 1980s, more Ramapithecus fossils were unearthed, including fragments of the face. They showed that the ape looked like an orangutan, not a human.
Palaeontologists were astonished, but molecular scientists were not. By now they had established that humans, chimps and gorillas were all closely related and shared a common ancestor within the last 11 million years or so, and that orangutans were slightly more distant relatives with a deeper prehistory. According to their thinking, a 14-million-year-old ape would be unlikely to look distinctly human, because it predated the appearance of the human lineage. But it might well look orangutan-like.
"The molecular people said 'See? We were right all along!'," says Schwartz.
In the 1980s and 90s, the molecular community built on such successes.
A western lowland gorilla (Gorilla gorilla gorilla) (Credit: Anup Shah/
A western lowland gorilla (Gorilla gorilla gorilla) (Credit: Anup Shah/
More sophisticated molecular techniques became available, allowing the scientists to compare apes in minute detail at the genetic level and work out which were most closely related to humans.
"The gorilla held out as a pretty good candidate," says Owen Lovejoy, an anthropologist at Kent State University in Ohio. "But eventually the chimpanzee won out."
By seven million years ago the European and Asian apes had vanished
Final confirmation that chimpanzees (and the closely related bonobos) are humanity's sister came in 1997, and it seemed to some that the LCA debate was drawing to a close. Huxley's work in the 1860s had encouraged many scientists to see the LCA as chimp-like, and the molecular work of the 1980s and 90s seemed to vindicate the idea.
"There began to be a more general acceptance of the implications that the LCA was likely to be more chimp-like," says Young.
This was not the only conclusion from the molecular work. The DNA studies also put an approximate date on the human-chimpanzee split: six or seven million years ago. It was a figure that considerably narrowed down the search for the LCA.
The fossil record shows that apes were widespread across Africa, Europe and Asia about 20 million years ago – at this time the world really was the Planet of the Apes. But by seven million years ago the European and Asian apes had vanished. If chimpanzees and humans split at this time, the LCA must have lived in Africa – in the same sort of environments occupied by modern chimps.
By the early 2000s, some physical anthropologists were even describing African apes like the chimpanzee as time machines into the earliest stages of human evolution.
The story should end there, but it does not. Surprisingly, the last 15 years has actually seen popular opinion begin to swing away from the idea of a chimp-like LCA, and towards a model closer to that argued by people like Straus in the 1940s.
Bornean orangutans (Pongo pygmaeus) (Credit: Anup Shah/
Bornean orangutans (Pongo pygmaeus) (Credit: Anup Shah/
There are several factors that explain the recent rethink. A more thorough understanding of chimp and gorilla anatomy helped.
There had been murmurings for some time that gorillas and chimpanzees (and bonobos) might not knuckle-walk in quite the same way. In 1999, Mike Dainton and Gabriele Macho at the University of Liverpool, UK, looked at the idea more formally. From subtle differences in the way gorilla and chimpanzee wrist bones change as the apes grow from juveniles to adults, Dainton and Macho concluded that the two may have evolved knuckle-walking independently.
Over the following decade, other researchers reported similar findings. By 2009, Tracy Kivell – now at the University of Kent, UK – and Daniel Schmitt at Duke University in Durham, North Carolina, were arguing that humans did not evolve from a knuckle-walking LCA.
Kivell says the 2009 paper received quite a lot of attention. She thinks this might be because it was published just a few months before one of the most complete and potentially important fossils for understanding human evolution was officially unveiled – one that some people think blows a huge hole in the idea that the LCA was chimp-like.
Artist's impression of Ardipithecus ramidus (Credit: National Geographic Creative/Alamy)
Artist's impression of Ardipithecus ramidus (Credit: National Geographic Creative/Alamy)
Late in 2009, a research team including Tim White and Owen Lovejoy published a collection of research papersdescribing the remarkably well-preserved skeleton of "Ardi" – a 4.4-million-year-old fossil of the species Ardipithecus ramidus, which White and his colleagues had discovered in Ethiopia.
Put simply, Ardi looked "primitive"
White and Lovejoy's careful analysis strongly suggested that Ardi habitually walked on two legs when she was on the ground. It was one of many features that suggested to them that Ardi should be considered an early human, or hominin – one that lived just a few million years after the LCA, and so provides us with our best idea yet of exactly how it looked.
This conclusion was significant, because in many respects Ardi's anatomy is not at all chimp-like. It is very unlikely she was either a knuckle-walker or a brachiating ape.
Ardi lived in a forest setting and must have spent time in trees as well as on the ground. But her anatomy suggests she was adapted to move around in those trees almost like a large monkey might, moving cautiously on feet that – unlike gorilla and chimp feet – seem to have been unsuitable for wrapping around branches for grip.
Put simply, Ardi looked "primitive" – and that suggested that the LCA looked primitive too.
What Ardi may have looked like (Credit: Ariadne Van Zandbergen/Alamy)
What Ardi may have looked like (Credit: Ariadne Van Zandbergen/Alamy)
Of course, the Ardi analysis was not uncontroversial. One of the implications of their interpretations was that all sorts of anatomical features shared by gibbons, orangutans, chimps and gorillas must have evolved independently in each of these apes.
People have begun to question what was an emerging consensus
"I think they took it a little too far," says Kivell. "Their model means that there is a lot of parallel evolution across all apes. I still think comparative studies with chimps and other African apes can provide a lot of insight into our own evolution."
Sergio Almécija at the George Washington University in Washington DC agrees. "I do believe that chimps could represent good models for the LCA for certain aspects – for instance body size, perhaps cognition," he says. But his own research has also helped to emphasise that chimps might not simply be living time machines from the time that the LCA was alive.
In 2015, for instance, Almécija and his colleagues published an analysis of ape hands that emphasised just how much the length of digits has evolved in chimpanzees since they split from the LCA. Judging by fossil evidence from earlier apes, human hands are surprisingly primitive in appearance – notwithstanding the fact that we evolved an opposable thumb after the split from the LCA.
Even the biologists studying modern primates are finding evidence that the LCA may not have been chimp-like.
Orangutans are our close relatives (Credit: Fiona Rogers/
Orangutans are our close relatives (Credit: Fiona Rogers/
In one 2013 study, Pavel Duda and Jan Zrzavý at the University of South Bohemia in the Czech Republic used what is known about living ape behaviour – and about the shape of the ape evolutionary tree – to try to estimate when certain traits first evolved. They suggested that sexual intercourse lasted longer in the LCA than in chimpanzees, and that the LCA males devoted more time to looking after offspring than chimp males do.
Apes were still flourishing in Europe as well as Africa 13 million years ago
Decades after Straus and a few other anatomists had argued that the chimpanzee was a poor model for the LCA, mainstream opinion has moved their way. "There has been a community shift, where people have begun to question what was an emerging consensus for a chimp-like LCA," says Young.
But even that is not the end of the story. There are still "chimp-like LCA" advocates out there, and they are fighting back.
For instance, in 2015 Young and his colleagues argued from the study of ape shoulder blades that the LCA might have had some features in common with chimps and gorillas after all, hinting that it might actually have been a brachiating ape. Such a conclusion would not have been controversial if it had been published a decade or so ago, Young says – but mainstream thought has shifted so far from the chimp-like LCA concept that the paper did, in fact, face some criticism.
Of course, only if and when fossils of the LCA itself come to light will the debate finally draw to a close. But the search for those crucial fossils is no longer quite as straightforward as it once seemed. In the last five years, some geneticists have begun to question whether the molecular clocks they use to estimate when the LCA lived are being read correctly. It is possible, they say, that the LCA might actually have lived 13 – not seven – million years ago.
Apes were still flourishing in Europe as well as Africa 13 million years ago, which means that in principle the LCA might have lived there.
Artist's impression of a Dryopithecus (Credit: Stocktrek Images Inc/Alamy)
Artist's impression of a Dryopithecus (Credit: Stocktrek Images Inc/Alamy)
Possible support for that idea comes from a 2015 analysis of an ape called Dryopithecus that lived in both Africa and Europe about 12.5 million years ago. David Begun, an anthropologist at the University of Toronto in Canada, concluded that Dryopithecus might be an early relative of the gorilla, and suggested that the LCA of humans and chimps might consequently have lived about 10 million years ago.
"It is not impossible that the LCA was European," says Begun – although there is no direct evidence for that yet, and he still favours the idea it was African.
There are also a few researchers who take a completely different view.
There is not yet universal agreement
For instance, Schwartz is adamant that it is orangutans, not chimpanzees, that are our sister species. It is an idea he first developed in the 1980s – before, he says, anthropologists "caved in" and conceded that molecules and not anatomy were the ultimate arbiters of the shape of the ape family tree.
Schwartz thinks DNA is not the infallible witness on evolution many assume it to be, and that there are many anatomical and behavioural similarities between humans and orangutans that should not simply be ignored. For instance, both have thick layers of enamel on their teeth, and female orangutans (like women) do not "advertise" to males when they are most fertile – something biologists call oestrus. "Orangs are the only other mammal I know of that don't have oestrus," says Schwartz.
To be clear, few researchers agree with Schwartz. But even putting his ideas to one side, it is clear that there is not yet universal agreement on the LCA.
It is true that, today, some researchers have a well-thought-through idea of what the LCA looked like and how it behaved. The trouble is that other researchers have equally well-reasoned models that suggest an LCA that looked and behaved in a completely different way. And that puts the research community in a bit of a quandary.
In principle, fossilised remains of the LCA might come to light any time. They might even be discovered this very year. But because there is so little agreement on what the LCA should look like, researchers will interpret the fossils differently.
"It's a problem that we might encounter," says Almécija. "Are we going to be able to recognise the LCA when we find it?"