For most of the 20th century, the model of human origins was a tree: with the trunk dividing into branches, and then twigs. Each species of human relative (hominin) was a neat, single branch.

As an undergraduate, I was taught that Homo sapiens was one of these branches that emerged in Africa, spread across the world, and displaced every archaic human it encountered.

Neanderthals, Homo erectus, and other ancient relatives were evolutionary dead ends – unfortunate cousins who left no descendants. In the 30 years since I left university, those early lessons are now radically revised.

That neat replacement story is now comprehensively wrong, largely thanks to studies like the one published in Nature this week by Qiaomei Fu from the Chinese Academy of Sciences and colleagues. The paper achieves something that would have seemed impossible a decade ago: it recovers meaningful biological information from H. erectus fossils far too old for DNA.

Instead of genetic sequences, the team extracted ancient proteins from the enamel of six teeth from three Chinese sites – Zhoukoudian (which, in the early 20th century, produced fossil remains known as “Peking Man”), Hexian and Sunjiadong – all dating to around 400,000 years ago.

Homo erectus is widely regarded as the first hominin to leave Africa; the evidence suggests this species had moved into Eurasia nearly two million years ago. It remains the most geographically widespread human ancestor that ever lived. The new study indicates that Homo erectus exchanged genes (probably through interbreeding) with Denisovans in East Asia roughly 400,000........

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