New genetic analyses of wild baboons in southern Kenya reveals that most of them carry traces of hybridization in their DNA. As a result of interbreeding, about a third of their genetic makeup consists of genes from another, closely-related species.
The study took place in a region near Kenya's Amboseli National Park, where yellow baboons occasionally meet and intermix with their anubis baboon neighbors that live to the northwest.
[...] By all accounts, the offspring of these unions manage just fine. Fifty years of observations turned up no obvious signs that hybrids fare any worse than their counterparts. Some even fare better than expected: baboons that carry more anubis DNA in their genome mature faster and form stronger social bonds, and males are more successful at winning mates.
But new genetic findings published Aug. 5 in the journal Science suggest that appearances can be deceiving.
Even modern humans carry around a mix of genes from now-extinct relatives. As much as 2% to 5% of the DNA in our genomes points to past hybridization with the Neanderthals and Denisovans, ancient hominins our ancestors encountered and mated with as they migrated out of Africa into Europe and Asia. Those liaisons left a genetic legacy that still lingers today, affecting our risk of depression, blood clots, even tobacco addiction or complications from COVID-19.
The researchers wanted to understand the possible costs and benefits of this genetic mixing in primates, including humans. But modern humans stopped interbreeding with other hominins tens of thousands of years ago, when all but one species -- ours -- went extinct. The wild baboons of Amboseli, however, make it possible to study primate hybridization that is still ongoing.
[...] Their results are in line with genetic research in humans, which suggests that our early ancestors paid a price for hybridizing too. But exactly what Neanderthal and Denisovan genes did to cause them harm has been hard to tease out of the limited fossil and DNA evidence that's available.
The researchers say that the baboons at Amboseli offer clues to the costs of the hybridization. Using RNA sequencing to measure gene activity in the baboons' blood cells, the researchers found that natural selection is more likely to weed out bits of borrowed DNA that act as switches, turning other genes on and off.
[...] "We're not saying this is what Neanderthal and Denisovans genes did in humans," added Tung, now at the Max Planck Institute for Evolutionary Anthropology in Germany. "But the baboon case makes it clear that genomic evidence for costs to hybridization can be consistent with animals that not only survive, but often thrive."
Journal Reference:
Tauras P. Vilgalys, Arielle S. Fogel, Jordan A. Anderson, et al., Selection against admixture and gene regulatory divergence in a long-term primate field study, Science, 377, 2022. DOI: 10.1126/science.abm4917
