December 1941. Japan has just entered the second world war. China, already fighting its neighbour, is in the firing line. At the Peking Union Medical College Hospital, Hu Chengzhi carefully packs two wooden crates with the world’s most precious anthropological artefacts. Peking Man – in reality some 200 fossilised teeth and bones, including six skulls – is to be shipped to the United States for safekeeping. This is the last anyone ever sees of him.

At the time, the Peking Man remains were the oldest known fossils belonging to human ancestors. Their discovery in the 1920s and 30s caused a sensation, triggering declarations that the cradle of humanity had been found. But just a few decades later, all eyes had turned to Africa. A slew of discoveries there left little doubt that it was our true ancestral home. As far as human evolution was concerned, Asia was out of the picture.

Ancient skulls flesh out China’s Neanderthal past

Not any more. The last decade has seen the discovery of new Asian fossils, among others by Chinese palaeoanthropologists with a renewed interest in their heritage. As key moments in our past are rewritten, the spotlight is once more turning to the East.

The first Peking Man remains were found in 1923, nearly 50km outside Beijing. Alongside the broad-nosed individuals with thick brows were burned animal bones, suggesting an early human ancestor capable of controlling fire. Only four other ancestral human species had been discovered at that time, including Neanderthals in Germany and Australopithecus africanus, identified from the apelike Taung Child remains in South Africa. Team leader Davidson Black believed the Chinese fossils represented a new species, which he called Sinanthropus pekinensis.

For a while, all the excitement in palaeoanthropology focused on east Asia. Then, in the 1950s, husband-and-wife team Louis and Mary Leakey began digging at Olduvai Gorge in Tanzania. By 1959, they had discovered a 1.8-million-year-old species, Paranthropus boisei.

This presaged a flood of remarkable discoveries in east Africa, including the earliest Homo species – Homo habilis – at Olduvai; footprints at nearby Laetoli, revealing that our ancestors walked upright at least 3.7 million years ago; and the famous “Lucy” (Australopithecus afarensis), that lived 3.2 million years ago, in Ethiopia. Peking Man and Asia were sidelined.

From these and subsequent discoveries emerged the standard model of human evolution. It traces our family tree back to a split with the forebears of chimps some six to 10 million years ago. The next few million years saw the evolution of a profusion of hominin species the length and breadth of Africa, before our own genus, Homo, emerged about two million years ago.

Homo erectus, an early member of our genus, clearly had a wanderlust. It migrated all the way to Southeast Asia as early as 1.8 million years ago.

My heart was racing: archaeologist on ‘hobbit’ fossil dig in Indonesia

As recently as July 11, scientists announced that newly discovered stone tools suggest some unidentified relative of humans lived in China as long as 2.1 million years ago – more than 200,000 years earlier than the previous record for such a presence outside Africa.

Today, Peking Man is recognised as a late representative that lived 700,000 years ago. While nobody disputes that several human species populated Eurasia very early on, the textbook version sees them as evolutionary dead ends. Our own species, the story goes, descends directly from African Homo erectus and only emerged from the continent some 60,000 years ago, at which point it swept across the globe, replacing all other hominin species.

That, until very recently, was the accepted story. There were details to fill out, but the plot and main characters were clear. As fossils trickled out of Asia, drawing far less attention in the West than African fossils did, they were often dismissed because they contradicted the dominant narrative.

In 1992, for instance, researchers reported finding a pair of 900,000-year-old skulls in Yunxian, in central China’s Hubei province. Their features looked like a mix of Homo erectus and Homo sapiens – which was odd because Homo sapiens should theoretically have been firmly sequestered in Africa at the time.

Dali Man, a 260,000-year-old skull found 14 years earlier in the central province of Shaanxi, had a similar mix of features, typical of “transitional forms”, that cannot be ascribed to any well-defined species. Although the Yunxian and Dali Man fossils are particularly fine examples, many more have been found in east Asia.

Then, in 2009, Chinese scientists announced the discovery of a 110,000-year-old jawbone in the southern province of Guangxi. Though relatively primitive, it displayed a prominent human-like chin. The team classified it as Homo sapiens, which would mean that our species was in Asia a good 50,000 years before we previously thought. Still, many were sceptical, reluctant to rewrite humanity’s origins. Some suggested it may have been a hybrid of Homo sapiens with another now-extinct species – though that would still imply that humans were in east Asia. Who or what the Guangxi remains belonged to is still hotly debated.

The traditional view, that modern humans swept out of Africa as a single exodus 60,000 years ago is now being called into question
Michael Petraglia, Max Planck Institute for the Science of Human History

The tide began to turn in 2015, when 47 teeth were found inside a cave in Daoxian, in Hunan province, also in southern China. Teeth are one of the best ways to distinguish between hominin species, and these were distinctly human – belonging to our own species – not to mention very old. According to Wu Liu at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing and his colleagues, they had been lying around for 80,000 to 120,000 years.

For Wu, the mounting evidence could only mean one thing: “Early modern humans were in southern China at least 100,000 years ago.”

That would put our species’ first foray out of Africa at least 40,000 years further back in time, yet this early Asian expansion hypothesis is gaining traction. “The traditional view, that modern humans swept out of Africa as a single exodus 60,000 years ago is now being called into question,” says Michael Petraglia at the Max Planck Institute for the Science of Human History, in Germany.

In December 2017, Petraglia co-authored a review that considers the “Asian perspective” on human evolution, drawing on all the evidence. “Palaeoanthropologists are now increasingly arguing, on the basis of fossil, archaeological and genetic evidence, that humans began spreading out of Africa by at least 120,000 years ago, and in multiple waves,” Petraglia says.

An earlier exit from Africa fits better with other recent discoveries. Just last year, a collection of Moroccan fossils suggested that our species could be 300,000 to 350,000 years old, adding at least 100,000 years to our history. Then, earlier this year, we learned that a group of Homo sapiens was living in what is now Israel at least 177,000 years ago.

Another group was making tools in south India at about the same time. And in April, reports of a fossilised finger bone pointed to the presence of Homo sapiens in what is now Saudi Arabia at least 85,000 years ago. Early humans clearly were not the stay-at-home types we once thought. There seems little doubt that our direct ancestors ventured east out of Africa far earlier than the standard narrative allows.

This is a huge change to the standard view. But it does not explain those weird transitional fossils from China that display a mix of Homo erectus and Homo sapiens features. Being hundreds of thousands of years old, they predate even the earlier exodus out of Africa. The most radical suggestion is that they are evidence that Homo erectus evolved into Homo sapiens in east Asia.

The idea that we evolved from a number of separate populations was once regarded as maverick, but has become more respectable

Wu Xinzhi, at the Chinese Academy of Sciences in Beijing, is the fiercest proponent of this suggestion, a form of “multi-regionalism”. The idea that we evolved from a number of separate populations was once regarded as maverick, but has become more respectable. Most notably, the latest evidence from inside Africa undermines the notion that Homo sapiens emerged from a single population in the east of the continent. Instead, most now agree there were isolated populations across Africa that sporadically came together and mated, creating a variety of human forms.

Wu Xinzhi’s suggestion, however, remains radical. He believes that the transitional fossils are evidence of Asian Homo erectus evolving into our own species in Asia, that Peking Man was an ancestor of modern Asian people and that Asia should have equal billing with Africa as the birthplace of our species. While some Chinese palaeontologists support this view, others see a hint of nationalism at play.

To bolster his argument that China’s hominins were evolving along similar lines to those in Africa, Wu Xinzhi, along with Sheela Athreya at Texas A&M University, recently showed that the Dali skull has many features in common with the early Homo sapiens fossils from Morocco. The genetic evidence, however, still points to a common African origin: 97 per cent of the DNA in Chinese populations can be traced back to Africa.

A more likely explanation for the transitional fossils is that Asia, like Africa, was once home to various human groups that exchanged genes. Along with Homo erectus, genetic studies have revealed a number of hominins whose identity is still a mystery. Later, there was the diminutive “hobbit”, Homo floresiensis, found on the Indonesian island of Flores from 100,000 years ago, preceded by an ancestral species going back 700,000 years.

Denisovans were probably there too. Although their identified remains currently amount to just three teeth and a finger bone found in Siberia, dental and genetic evidence indicate they were also in Southeast Asia. Even Neanderthals, which have only been positively identified as far east as central Asia’s Altai Mountains, may once have roamed further east. Their characteristic features are now being identified in Chinese fossils.

If these various species interbred, they should have left behind hybrids scattered across Asia. Indeed, the surprisingly rich variety among east Asian fossils suggests hybridisation was widespread, says María Martinón-Torres, director of the National Research Centre on Human Evolution, in Burgos, Spain.

Martinón-Torres and her colleagues have also shown that hominins in Africa and Eurasia did evolve relatively independently for a long time. When they examined 5,000 fossil teeth spanning 2.5 million years, they found that each continent had its own distinct type of teeth – strong evidence that Eurasia was a centre of speciation in its own right.

Maybe Africa was not the only human cradle
María Martinón-Torres, National Research Centre on Human Evolution

Rather than multi-regionalism, she and her collaborators suggest a “source and sink” model to explain the human settlement of east Asia. They believe the huge variety of fossils points to repeated colonisation, interbreeding and extinctions, with populations thriving and disappearing depending on fluctuations in the climate over hundreds of thousands of years. During cold periods, much of central Asia and the northern steppe would have become uninhabitable. These are the “sinks”. But hominins would have been able to survive in more southerly regions, on some islands and in regions where the climate remained relatively stable, such as the Middle East – the “sources”.

If correct, this points to a strong but discontinuous occupation of east Asia. Although Martinón-Torres does not believe that our species arose independently in Asia, she does think it likely that we have roots in Asia, though probably not in the Far East.

Peking Man was a true pioneer, but most of his relatives did not travel nearly as far, settling instead in the Middle East, where the climate was more favourable. This, she suggests, was the source population of Neanderthals, Denisovans and another branch of our family tree, which migrated back to Africa before evolving there into Homo sapiens. “Maybe Africa was not the only human cradle,” she says.

The truth is, the story of our evolution is still being rewritten and we cannot be sure how it will turn out. What is certain is that Asia can no longer be sidelined. It is possible that the species we evolved from made its own migration into Africa before giving rise to us. Our ancestors then left Africa at least 100,000 years ago and travelled the breadth of Eurasia for millennia.

New Scientist