What fossils reveal about the interbreeding of early humans

Early modern humans (left) and Neanderthals. Credit: Artistic Illustration: Gulliver Prieto; Copyright: K. Harvati

Many people living today have a small component of Neanderthal DNA in their genes, suggesting an important role for mixing with ancient human lineages in the evolution of our species. Ancient evidence suggests that interbreeding with Neanderthals and other ancient groups occurred several times, with the history of our species being more like a network or braided stream than a tree. It is clear that the origin of humanity was more complex than previously thought.

It is necessary to use multiple lines of evidence to investigate the effect of this crossbreeding. Ancient DNA is rarely well preserved fossil specimens, so scientists need to identify potential hybrids from their skeletons. This is vital to understanding our complex past and what makes us human. Professor Katrina Harvati of the Senckenberg Center for Human Evolution and Palaeolithic Ecology at the University of Tübingen, Germany, together with Professor Rebecca Ackermann of the Institute for Human Evolution Research at the University of Cape Town, South Africa, have investigated the impact of interbreeding using fossil skulls and possible individual hybrids identified in the past. Their work has been published in the magazine Nature’s environment and evolution.

Accurate data analysis

To do this, the researchers investigated a large number of fossil remains of ancient humans from the Upper Paleolithic in Eurasia, dating from approximately 40 to 20 thousand years ago. Many of these individuals have yielded ancient DNA that shows a small component of Neanderthal ancestry in their genes, reflecting their recent admixture with this group. they skull bones It was compared with samples (not mixed) of Neanderthals and early, as well as modern, modern humans from Africa.

The researchers examined three regions of the skull: the mandible, the brain and the face, looking for signs of hybridization. “These might include, for example, intermediate morphology compared to Neanderthals or modern humans, dental abnormalities or unusual sizes. These are traits we see in hybrids of different mammals, including primates,” explain Harvati and Ackermann. Their study showed that the signals of hybridization were evident in the brain and jaws, but not in the faces.

in well-known individuals genetic backgroundIn the study, the researchers also looked at whether the cross-hybridization marks on the skeleton matched the percentage of Neanderthal ancestors. The fact that it does not indicate that “the presence of certain genetic variants may be more important than the overall proportion of Neanderthal ancestry,” the researchers say.

Harvati and Ackermann also identified some of the individuals studied as possible hybrids, including individuals from the Middle East – known to be a contact area for the groups – but also outside, in both Western and Eastern Europe. However, “where possible, the status of an individual hybrid should be confirmed using genetic data, and as such we consider these definitions as hypotheses to be tested,” says Harvati. This was the first study of its kind, she says, adding, “We hope this will encourage researchers to look more closely at these fossils and combine multiple lines of evidence to identify interbreeding in the fossil record.”

evolution innovator

In other living things – from plants to large mammalsCrossbreeding is known to produce evolutionary innovation, including new and diverse outcomes. “It is estimated that about 10 percent of animal species produce hybrids, including, for example, cows, bears, cats and dogs,” Ackermann says. Hybrids are also known in primates, our close relatives, such as baboons, she says. “Because hybridization It introduces new diversity, creates new combinations of diversity, and this can facilitate particularly rapid evolution, particularly when faced with new or changing environmental conditions.”

Therefore, crossbreeding may have provided ancient humans with genes and anatomical features This gave them important advantages when spreading from Africa across the world, resulting in our diverse bodily species and evolutionarily resilient, the authors say.

Baboons borrowed a third of their genes from their cousins

more information:
Katrina Harvati, Incorporating morphological and genetic evidence to assess crossbreeding in hominins from the late Western Pleistocene, Nature’s environment and evolution (2022). DOI: 10.1038 / s41559-022-01875-z. www.nature.com/articles/s41559-022-01875-z

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