Humans and Neanderthals have kept reproduction – and reproduction – for ages

Humans today are mosaics, our genome rich in interlaced tapestries. Each fossil discovered, each DNA analysis performed, the story becomes more complex: we, the only survivors of the genus Homo, harbor genetic fragments of other closely related but long-vanished lineages. The modern man is the product of a sprawling history of changes and dispersions, separations and reunions – a story characterized by a much greater diversity, movement and mix than it n & # 39; It seemed imaginable about ten years ago.

But it is one thing to say that the Neanderthals have crossed with the ancestors of modern Europeans, or that the newly discovered Denisovans have crossed with a group of older mysteries, or that they have all crossed. This is another way of providing concrete details about when and where these pairings occur. "We have this picture where these events occur everywhere," said Aylwyn Scally, an evolving geneticist at Cambridge University. "But it's very hard for us to pin down a particular event and say, yes, we're really convinced that this one happened – unless we have an old DNA."

You think that you are only watching a Neanderthal, but actually a mixture of Neanderthal and modern human.
Adam Siepel, Cold Spring Harbor Laboratory

The events that are unfolding are relatively recent, starting with the migration of modern men out of Africa 60,000 years ago, during which they exchanged with homininous relatives (such as Neanderthals and Denisovans) that They met on the way. Evidence of miscegenation during any migration prior to this date or at events that occurred earlier in Africa was difficult to pin down.

Now this is starting to change. Partly because of greater computing power, "we are starting to see the next wave of method development," he said. Joshua Akey, professor of genomics at the Lewis-Sigler Institute of Integrative Genomics at Princeton University. "And that allows us to start making new inferences from the data … that the previous generation of methods could not do."

While scientists look further into the past and discover evolutionary relationships with unprecedented details, their discoveries complicate the narrative of human history and save from the darkness of the chapters that were lacking before. Clues are emerging as to the unexpected influence of the gene flow of old hominins on modern human populations before they leave Africa. Some researchers even identify the genetic contributions that modern humans might have made to these other lineages, thus completely reversing the usual scientific field. Confused and so intimately connected with these many effects, they have all shaped humanity as we know it now.

Old humans, new towers

When researchers first retrieved Neanderthal bone DNA, the techniques available to understand it were powerful but relatively simple. Scientists have compared ancient and modern sequences, identified shared sites and mutations, and conducted global statistical analyzes. Thus, in 2010, they discovered that Neanderthal DNA accounts for about 2% of the genome of people of non-African ancestry, a result of miscegenation occurring throughout Eurasia between 50,000 and 60,000 years ago. This is how they discovered that Denisovan's DNA accounts for about 3% of the genome of Papua New Guinea and Australia.

"But this kind of very simple approach is not very effective at solving the complexity" of the interaction of these lost populations, said John Hawks, paleoanthropologist at the University of Wisconsin, Madison. This does not allow researchers to test specific hypotheses on the progress of this hybridization.