Research finds hidden selection against interbreeding in baboons

A new study based in Africa reveals hidden selection against interspecies breeding in wild baboon species in a strikingly similar way to what has been described for archaic hominins. The findings, based on coupled genomic and long-term field data, highlight the crucial role of other living primates as models for understanding human evolution, particularly for phenomena that are impossible to study in our lineage alone. Genetic admixture is widely considered to be central to primate evolution. It is well known that the ancestors of modern humans intermixed with Neanderthals and other close, now-extinct Homo lineages, leaving a genetic legacy that shapes human variation and our current conceptions of human origins today. Although previous studies have suggested that selection against hybrid individuals would have acted against hominin interbreeding, testing such a hypothesis remains difficult. However, hybridization is observed in many of our close primate relatives, suggesting that other living primates could provide context for understanding admixture in our own lineage. To investigate primate admixture in the wild, Tauras Vilgalys investigated hybridization between yellow baboons and anubis baboons (two common primate models for human genetic studies) from the Amboseli region of Kenya. Vilgalys et al. combined data from 50 years of field observations on population dynamics and demography with genomic data from roughly nine generations of hybrid baboons. While the behavioral and life history field data suggest that hybrid baboons suffer no clear cost to fitness, the genomic analysis revealed contrasting evidence for selection against admixture that is consistent with results from archaic humans. The findings may help explain how primate species divergence is maintained in the face of frequent interspecific gene flow. Vilgalys et al. note, however, that the mode of selection against hybrids remains unclear and is an important question to be addressed in future work.