What Fossils Reveal About Early Human Hybrids

What Fossils Reveal About Early Human Hybrids

Early modern humans (left) and Neanderthals. Image credit: Artistic illustration: Gleiver Prieto; Copyright: K. Harvati

Many people living today have a small portion of Neanderthal DNA in their genes, suggesting that mixing with ancient human lineages played an important role in the evolution of our species. Paleontological evidence suggests that interbreeding with Neanderthals and other ancient groups occurred multiple times, and the history of our species is more like a network or braided stream than a tree. Clearly, human origins are more complex than previously thought.

Multiple lines of evidence must be used to study the effects of this hybridization. Ancient DNA is rarely well preserved in fossil specimens, so scientists need to identify possible hybrids from the bones. This is critical to understanding our complex past and what makes us human. Professor Katerina Harvati of the Senckenberg Centre for Human Evolution and Paleoenvironment, University of Tübingen, Germany, and Professor Rebecca R. Ackermann of the Institute of Human Evolution, University of Cape Town, South Africa, studied the impact of hybridization. Fossilized bones, and individual potential hybrids have been identified in the past.Their work has been published in journals natural ecology and evolution.

Analyze the data carefully

To this end, the researchers investigated a large collection of ancient human fossil remains from the late Paleolithic period in Eurasia, which date back to about 400,000 to 20,000 years ago. Some of these people have produced ancient DNA that shows a small amount of Neanderthal ancestry in their genes, reflecting their recent admixture with the group. Their skulls were compared with (unmixed) samples from Neanderthals and early and more recently modern humans from Africa.

The researchers examined three areas of the skull: the mandible, the skull and the face, looking for signs of hybridization. “These may include, for example, intermediate morphologies, unusual or unusual sizes of teeth compared to Neanderthals or modern humans. These are things we see in hybrids of various mammals, including primates. characteristics,” explain Harvati and Ackermann. Their study showed that hybridization signals were evident in the braincase and jaw, but not in the face.

Among individuals with known genetic backgrounds, the researchers also considered whether evidence of hybridization on the bones matched the percentage of Neanderthal ancestry. This fact does not suggest that “the presence of specific genetic variants may be more important than the overall proportion of Neanderthal ancestry,” the researchers said.

Harvati and Ackermann also identified some of the individuals studied as potential hybrids, including individuals from the Middle East—a region known to be the contact area for these groups—but also other parts of Western and Eastern Europe. However, “where possible, genetic data should be used to confirm the interbreeding status of individuals, so we treat these identifications as hypotheses that need to be tested,” Harvati said. This is the first study of its kind, she said, adding: “We hope this will encourage researchers to look more closely at these fossils and combine multiple lines of evidence to identify hybridization in the fossil record.”

Evolutionary Innovator

In other organisms — from plants to large mammals — hybridization is known to produce evolutionary innovations, including novel and diverse outcomes. “It’s estimated that about 10 percent of animal species produce hybrids, including bovines, bears, felines and canines,” Ackerman said. There are also hybrids among primates, our closest relatives, such as baboons, she said. “Because hybridization introduces new variants and creates new combinations of variants, this can facilitate particularly rapid evolution, especially in the face of new or changing environmental conditions.”

Thus, interbreeding may have provided ancient humans with genetic and anatomical traits that gave them an important advantage as they spread from Africa to other parts of the world, resulting in our physically diverse and evolutionarily resilient species, the authors say.

These baboons borrowed a third of their genes from their cousins

More information:
Katerina Harvati, Merging morphological and genetic evidence to assess the interbreeding of Western Eurasian Late Pleistocene hominins, natural ecology and evolution (2022). DOI: 10.1038/s41559-022-01875-z. www.nature.com/articles/s41559-022-01875-z

Courtesy of the University of Tübingen

Citation: What Fossils Reveal About Early Human Hybridization (September 5, 2022) Retrieved September 5, 2022 from https://phys.org/news/2022-09-fossils-reveal-hybridization-early-humans .html

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