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 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 years ago. The study suggests that some of that genetic legacy, it now appears, was passed on to living people in the Philippines, Papua New Guinea, and across south-east Asia.
Tooth enamel is the hardest tissue in the body, and its proteins survive long after DNA has degraded beyond recovery. What the team found in those proteins is striking. All six specimens share a previously unknown amino acid variant – a tiny molecular signature, a single letter changed in the protein sequence, never seen in any other hominin alive or dead.
This variant clusters these east Asian H. erectus into a distinct group, confirming their identity and settling a long-running debate about whether the unusual Hexian fossils were H. erectus at all. A second variant they share, however, is not unique to H. erectus. It also appears in Denisovans – a mysterious archaic (non-Homo sapiens) human group known mainly from a cave in Siberia.
Extract — continue reading at the source.
