At one time, we thought that humans evolved in a straight line, from one species to another, until homo sapiens sapiens, or modern humans, were achieved -as illustrated in the artwork called March of Progress. But as we developed the ability to analyze DNA, the story gets much messier. Several species of hominins co-existed over the course of our evolution, possibly many species at different times. We now know that non-African humans carry a small percentage of Neanderthal genes, and some carry Denisovan genes. Even more recent genetic research shows that those Neanderthals that modern humans encountered when they left Africa 60,000 years ago already had a legacy of mixing with modern humans in their genome!
The finding also adds to the already compelling body of evidence that there were multiple migrations of modern humans out of Africa, stretching back over hundreds of thousands of years. Modern humans were thought to have evolved in Africa after the departure of Neanderthals and Denisovans, and to have remained on the continent until their well-known out-of-Africa diaspora 60,000 years ago. But recently, fossil evidence has indicated otherwise: A human jawbone in Israel, reported last year to date back to 180,000 years ago, and a skull fragment in Greece that’s even older, indicate earlier human migrations.
In fact, with that piece of skull, archaeologists may have stumbled across a possible member of the long-ago exodus that Siepel and his team inferred in their genomic study. The fossil, which was classified as Neanderthal when it was unearthed in Greece in the 1970s, was analyzed last month by the paleoanthropologist Katerina Harvati of the University of Tübingen and her colleagues. Structurally, it looked somewhat like a modern human skull, but it was estimated to be about 210,000 years old — supposedly too old to be modern at that location.
Under this model, it appears that modern humans didn't survive the earlier migrations, and the Neanderthals and Denisovans did not survive the last large homo sapiens sapiens migration. Or did they? The traces of DNA left after each exodus show they are still with us in some ways. Read more about how genome sequencing is revealing more about human evolution at Quanta magazine. -via Digg
(Image credit: Olena Shmahalo/Quanta Magazine)