Neanderthal ancestry through time: Insights from genomes of ancient and present-day humans
Gene flow from Neanderthals has shaped genetic and phenotypic variation in modern humans. We generated a catalog of Neanderthal ancestry segments in more than 300 genomes spanning the past 50,000 years. We examined how Neanderthal ancestry is shared among individuals over time. Our analysis revealed that the vast majority of Neanderthal gene flow is attributable to a single, shared extended period of gene flow that occurred between 50,500 to 43,500 years ago, as evidenced by ancestry correlation, colocalization of Neanderthal segments across individuals, and divergence from the sequenced Neanderthals. Most natural selection?positive and negative?on Neanderthal variants occurred rapidly after the gene flow. Our findings provide new insights into how contact with Neanderthals shaped modern human origins and adaptation. Gene flow from archaic hominins into modern humans, and vice versa, has been amply demonstrated in recent years. However, many questions remain about how selection has acted on introgressed variants as well as the diversity of hominin individuals who contributed to this admixture. Iasi et al. identified Neanderthal ancestry in genomic data from 59 ancient and 275 present-day human samples. They found that gene flow likely happened over a period of about 6000 years, and that positive and negative selection acted within about 100 generations on these introgressed segments. Surprisingly, the authors didn?t find evidence for a second pulse of introgression into East Eurasians despite the increased levels of introgression found in modern individuals. ?Corinne SimontiGene flow from Neanderthals has shaped genetic and phenotypic variation in modern humans. We generated a catalog of Neanderthal ancestry segments in more than 300 genomes spanning the past 50,000 years. We examined how Neanderthal ancestry is shared among individuals over time. Our analysis revealed that the vast majority of Neanderthal gene flow is attributable to a single, shared extended period of gene flow that occurred between 50,500 to 43,500 years ago, as evidenced by ancestry correlation, colocalization of Neanderthal segments across individuals, and divergence from the sequenced Neanderthals. Most natural selection?positive and negative?on Neanderthal variants occurred rapidly after the gene flow. Our findings provide new insights into how contact with Neanderthals shaped modern human origins and adaptation. Gene flow from archaic hominins into modern humans, and vice versa, has been amply demonstrated in recent years. However, many questions remain about how selection has acted on introgressed variants as well as the diversity of hominin individuals who contributed to this admixture. Iasi et al. identified Neanderthal ancestry in genomic data from 59 ancient and 275 present-day human samples. They found that gene flow likely happened over a period of about 6000 years, and that positive and negative selection acted within about 100 generations on these introgressed segments. Surprisingly, the authors didn?t find evidence for a second pulse of introgression into East Eurasians despite the increased levels of introgression found in modern individuals. ?Corinne Simonti
doi: 10.1126/science.adq3010
