Sumei Zhou

Reconstructing ancient population size history is essential for understanding the evolutionary origin of Homo sapiens. We recently developed the fast infinitesimal time coalescent process (FitCoal) and detected a severe population bottleneck occurring approximately 930 thousand years ago. However, two recent studies compared FitCoal and mushi and concluded that the severe bottleneck is a statistical artifact. In this study, we compared the two methods against a benchmark of ten billion msprime coalescent simulations. We demonstrate that FitCoal achieves both superior speed and accuracy in expected site frequency spectrum (SFS) estimation. Analyses of simulated datasets confirmed that FitCoal reliably recovers the bottleneck, whereas mushi fails under identical conditions. Independent fossil and paleoclimate evidence is consistent with the timing and evolutionary impact of this bottleneck, including associations with hominin dispersals, speciation events, and a subsequent increase in brain size. These findings refine the demographic history of Homo during the Pleistocene and highlight the importance of high-precision SFS computation for revealing critical evolutionary transitions that shaped modern human ancestry.

Reconstructing ancient population size history is essential for understanding the evolutionary origin of Homo sapiens . Using the fast infinitesimal time coalescent process (FitCoal), which precisely computes the expected site frequency spectrum (SFS), we revisited the debated population bottleneck that occurred approximately 930 thousand years ago. By benchmarking FitCoal against mushi and ten billion coalescent simulations, we demonstrate that FitCoal achieves both superior speed and accuracy in expected SFS estimation. Analyses of simulated datasets confirmed that FitCoal reliably recovered the bottleneck, whereas mushi failed under identical conditions. Independent fossil and paleoclimate evidence further corroborates the timing and evolutionary impact of this bottleneck, linking it to hominin dispersals, speciation events, and a subsequent increase in brain size. These findings refine the demographic history of Homo during the Pleistocene and highlight the importance of high-precision SFS computation for revealing critical evolutionary transitions that shaped modern human ancestry.

The emergence of social structure and organization is essential for the evolution of amniotes, including human beings. Sociability and social hierarchy are two key features to form a social group. However, it remains unknown whether sociability and social hierarchy are genetically separable. In this study, we examined the social hierarchy, social and social novelty preference of PAS1 (placental-accelerated sequence 1) knock-out and knock-in mice. PAS1 is a social enhancer that modulates social hierarchy. We found that PAS1 knock-out mice lack social hierarchy while wallaby/chicken PAS1 knock-in mice establish stable social ranks. Moreover, social and social novelty preference was observed in all PAS1-mutated mice. PAS1 knock-in mice have stronger preference to interact with other mice than wild-type mice (C57BL/6). No aggressive alteration was found in PAS1-mutated mice. Overall, our results showed that PAS1 is an indispensable regulatory element in the formation of social hierarchy while PAS1 regulates one of pathways modulating sociability. Therefore, sociability is genetically separable from social hierarchy in amniotes, providing insights into how social structure and organization evolved. Highlights PAS1, a social enhancer, is indispensable for amniotes to establish social hierarchy. PAS1 modulates sociability in amniotes. Sociability and social hierarchy are regulated differently in amniotes. The frequency of PAS1 allele was not rare when social hierarchy first appeared.