JULY 13, 2016

9 MIN READ

How China Is Rewriting the Book on Human

Origins
Fossil finds in China are challenging ideas about the evolution of modern humans and our closest
relatives
BY JANE QIU & NATURE MAGAZINE

Replica skull of Peking Man.

Credit:
Yan Li via Wikimedia Commons CC by 3.0
Evolution

On the outskirts of Beijing, a small limestone mountain named Dragon Bone Hill rises above the
surrounding sprawl. Along the northern side, a path leads up to some fenced-off caves that draw
150,000 visitors each year, from schoolchildren to grey-haired pensioners. It was here, in 1929,
that researchers discovered a nearly complete ancient skull that they determined was roughly half
a million years old. Dubbed Peking Man, it was among the earliest human remains ever
uncovered, and it helped to convince many researchers that humanity first evolved in Asia.

Since then, the central importance of Peking Man has faded. Although modern dating methods
put the fossil even earlier — at up to 780,000 years old — the specimen has been eclipsed by
discoveries in Africa that have yielded much older remains of ancient human relatives. Such
finds have cemented Africa's status as the cradle of humanity — the place from which modern
humans and their predecessors spread around the globe — and relegated Asia to a kind of
evolutionary cul-de-sac.

But the tale of Peking Man has haunted generations of Chinese researchers, who have struggled
to understand its relationship to modern humans. “It's a story without an ending,” says Wu
Xinzhi, a palaeontologist at the Chinese Academy of Sciences' Institute of Vertebrate
Paleontology and Paleoanthropology (IVPP) in Beijing. They wonder whether the descendants of
Peking Man and fellow members of the species Homo erectus died out or evolved into a more
modern species, and whether they contributed to the gene pool of China today.

Keen to get to the bottom of its people's ancestry, China has in the past decade stepped up its
efforts to uncover evidence of early humans across the country. It is reanalysing old fossil finds
and pouring tens of millions of dollars a year into excavations. And the government is setting up
a $1.1-million laboratory at the IVPP to extract and sequence ancient DNA.

The investment comes at a time when palaeoanthropologists across the globe are starting to pay
more attention to Asian fossils and how they relate to other early hominins — creatures that are
more closely related to humans than to chimps. Finds in China and other parts of Asia have made
it clear that a dazzling variety of Homo species once roamed the continent. And they are
challenging conventional ideas about the evolutionary history of humanity.

“Many Western scientists tend to see Asian fossils and artefacts through the prism of what was
happening in Africa and Europe,” says Wu. Those other continents have historically drawn more
attention in studies of human evolution because of the antiquity of fossil finds there, and because
they are closer to major palaeoanthropology research institutions, he says. “But it's increasingly
clear that many Asian materials cannot fit into the traditional narrative of human evolution.”

Chris Stringer, a palaeoanthropologist at the Natural History Museum in London, agrees. “Asia
has been a forgotten continent,” he says. “Its role in human evolution may have been largely
under-appreciated.”

EVOLVING STORY
 In its typical form, the story of Homo sapiens starts in Africa. The exact details vary from one
telling to another, but the key characters and events generally remain the same. And the title is
always 'Out of Africa'.

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In this standard view of human evolution, H. erectus first evolved there more than 2 million
years ago (see 'Two routes for human evolution'). Then, some time before 600,000 years ago, it
gave rise to a new species: Homo heidelbergensis, the oldest remains of which have been found
in Ethiopia. About 400,000 years ago, some members of H. heidelbergensis left Africa and split
into two branches: one ventured into the Middle East and Europe, where it evolved into
Neanderthals; the other went east, where members became Denisovans — a group first
discovered in Siberia in 2010. The remaining population of H. heidelbergensis in Africa
eventually evolved into our own species, H. sapiens, about 200,000 years ago. Then these early
humans expanded their range to Eurasia 60,000 years ago, where they replaced local hominins
with a minuscule amount of interbreeding.

A hallmark of H. heidelbergensis — the potential common ancestor of Neanderthals, Denisovans

and modern humans — is that individuals have a mixture of primitive and modern features. Like
more archaic lineages, H. heidelbergensis has a massive brow ridge and no chin. But it also
resembles H. sapiens, with its smaller teeth and bigger braincase. Most researchers have
viewedH. heidelbergensis — or something similar — as a transitional form between H.
erectus and H. sapiens.

Unfortunately, fossil evidence from this period, the dawn of the human race, is scarce and often
ambiguous. It is the least understood episode in human evolution, says Russell Ciochon, a
palaeoanthropologist at the University of Iowa in Iowa City. “But it's central to our
understanding of humanity's ultimate origin.”

The tale is further muddled by Chinese fossils analysed over the past four decades, which cast
doubt over the linear progression from African H. erectus to modern humans. They show that,
between roughly 900,000 and 125,000 years ago, east Asia was teeming with hominins endowed
with features that would place them somewhere between H. erectus and H. sapiens, says Wu
(see‘Ancient human sites’).

“Those fossils are a big mystery,” says Ciochon. “They clearly represent more advanced species
than H. erectus, but nobody knows what they are because they don't seem to fit into any
categories we know.”

The fossils' transitional characteristics have prompted researchers such as Stringer to lump them
with H. heidelbergensis. Because the oldest of these forms, two skulls uncovered in Yunxian in
Hubei province, date back 900,000 years, Stringer even suggests that H. heidelbergensis might
have originated in Asia and then spread to other continents.

But many researchers, including most Chinese palaeontologists, contend that the materials from
China are different from European and African H. heidelbergensis fossils, despite some apparent
similarities. One nearly complete skull unearthed at Dali in Shaanxi province and dated to
250,000 years ago, has a bigger braincase, a shorter face and a lower cheekbone than most H.
heidelbergensis specimens, suggesting that the species was more advanced.

Such transitional forms persisted for hundreds of thousands of years in China, until species
appeared with such modern traits that some researchers have classified them as H. sapiens. One
of the most recent of these is represented by two teeth and a lower jawbone, dating to about
100,000 years ago, unearthed in 2007 by IVPP palaeoanthropologist Liu Wu and his colleagues.
Discovered in Zhirendong, a cave in Guangxi province, the jaw has a classic modern-human
appearance, but retains some archaic features of Peking Man, such as a more robust build and a
less-protruding chin.

Most Chinese palaeontologists — and a few ardent supporters from the West — think that the
transitional fossils are evidence that Peking Man was an ancestor of modern Asian people. In this
model, known as multiregionalism or continuity with hybridization, hominins descended
from H. erectus in Asia interbred with incoming groups from Africa and other parts of Eurasia,
and their progeny gave rise to the ancestors of modern east Asians, says Wu.

Support for this idea also comes from artefacts in China. In Europe and Africa, stone tools
changed markedly over time, but hominins in China used the same type of simple stone
instruments from about 1.7 million years ago to 10,000 years ago. According to Gao Xing, an
archaeologist at the IVPP, this suggests that local hominins evolved continuously, with little
influence from outside populations.

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POLITICS AT PLAY?

Some Western researchers suggest that there is a hint of nationalism in Chinese palaeontologists'
support for continuity. “The Chinese — they do not accept the idea that H. sapiens evolved in
Africa,” says one researcher. “They want everything to come from China.”
Chinese researchers reject such allegations. “This has nothing to do with nationalism,” says Wu.
It's all about the evidence — the transitional fossils and archaeological artefacts, he says.
“Everything points to continuous evolution in China from H. erectus to modern human.”

But the continuity-with-hybridization model is countered by overwhelming genetic data that

point to Africa as the wellspring of modern humans. Studies of Chinese populations show that
97.4% of their genetic make-up is from ancestral modern humans from Africa, with the rest
coming from extinct forms such as Neanderthals and Denisovans. “If there had been significant
contributions from Chinese H. erectus, they would show up in the genetic data,” says Li Hui, a
population geneticist at Fudan University in Shanghai. Wu counters that the genetic contribution
from archaic hominins in China could have been missed because no DNA has yet been recovered
from them.

Many researchers say that there are ways to explain the existing Asian fossils without resorting
to continuity with hybridization. The Zhirendong hominins, for instance, could represent
an exodus of early modern humans from Africa between 120,000 and 80,000 years ago. Instead
of remaining in the Levant in the Middle East, as was thought previously, these people could
have expanded into east Asia, says Michael Petraglia, an archaeologist at the University of
Oxford, UK.

Other evidence backs up this hypothesis: excavations at a cave in Daoxian in China's Hunan
province have yielded 47 fossil teeth so modern-looking that they could have come from the
mouths of people today. But the fossils are at least 80,000 years old, and perhaps 120,000 years
old, Liu and his colleagues reported last year. “Those early migrants may have interbred with
archaic populations along the way or in Asia, which could explain Zhirendong people's primitive
traits,” says Petraglia.

Another possibility is that some of the Chinese fossils, including the Dali skull, represent the
mysterious Denisovans, a species identified from Siberian fossils that are more than 40,000 years
old. Palaeontologists don't know what the Denisovans looked like, but studies of DNA recovered
from their teeth and bones indicate that this ancient population contributed to the genomes of
modern humans, especially Australian Aborigines, Papua New Guineans and Polynesians —
suggesting that Denisovans might have roamed Asia.

María Martinón-Torres, a palaeoanthropologist at University College London, is among those

who proposed that some of the Chinese hominins were Denisovans. She worked with IVPP
researchers on an analysis, published last year, of a fossil assemblage uncovered at Xujiayao in
Hebei province — including partial jaws and nine teeth dated to 125,000–100,000 years ago. The
molar teeth are massive, with very robust roots and complex grooves, reminiscent of those from
Denisovans, she says.

A third idea is even more radical. It emerged when Martinón-Torres and her colleagues
compared more than 5,000 fossil teeth from around the world: the team found that Eurasian
specimens are more similar to each other than to African ones. That work and more recent
interpretations of fossil skulls suggest that Eurasian hominins evolved separately from African
ones for a long stretch of time. The researchers propose that the first hominins that left Africa 1.8
million years ago were the eventual source of modern humans. Their descendants mostly settled
in the Middle East, where the climate was favourable, and then produced waves of transitional
hominins that spread elsewhere. One Eurasian group went to Indonesia, another gave rise to
Neanderthals and Denisovans, and a third ventured back into Africa and evolved into H. sapiens,
which later spread throughout the world. In this model, modern humans evolved in Africa, but
their immediate ancestor originated in the Middle East.

Not everybody is convinced. “Fossil interpretations are notoriously problematic,” says Svante
Pääbo, a palaeogeneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig,
Germany. But DNA from Eurasian fossils dating to the start of the human race could help to
reveal which story — or combination — is correct. China is now making a push in that direction.
Qiaomei Fu, a palaeogeneticist who did her PhD with Pääbo, returned home last year to establish
a lab to extract and sequence ancient DNA at the IVPP. One of her immediate goals is to see
whether some of the Chinese fossils belong to the mysterious Denisovan group. The prominent
molar teeth from Xujiayao will be an early target. “I think we have a prime suspect here,” she
says.

FUZZY PICTURE

Despite the different interpretations of the Chinese fossil record, everybody agrees that the
evolutionary tale in Asia is much more interesting than people appreciated before. But the details
remain fuzzy, because so few researchers have excavated in Asia.

When they have, the results have been startling. In 2003, a dig on Flores island in Indonesia
turned up a diminutive hominin, which researchers named Homo floresiensis and dubbed the
hobbit. With its odd assortment of features, the creature still provokes debate about whether it is
a dwarfed form of H. erectus or some more primitive lineage that made it all the way from
Africa to southeast Asia and lived until as recently as 60,000 years ago. Last month, more
surprises emerged from Flores, where researchers found the remains of a hobbit-like hominin in
rocks about 700,000 years old.

Recovering more fossils from all parts of Asia will clearly help to fill in the gaps. Many
palaeoanthropologists also call for better access to existing materials. Most Chinese fossils —
including some of the finest specimens, such as the Yunxian and Dali skulls — are accessible
only to a handful of Chinese palaeontologists and their collaborators. “To make them available
for general studies, with replicas or CT scans, would be fantastic,” says Stringer. Moreover,
fossil sites should be dated much more rigorously, preferably by multiple methods, researchers
say.

But all agree that Asia — the largest continent on Earth — has a lot more to offer in terms of
unravelling the human story. “The center of gravity,” says Petraglia, “is shifting eastward.”

This article is reproduced with permission and was first published on July 12, 2016.

JANE QIU is an award-winning science writer based in Beijing.

More by Jane Qiu
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