️ Episode 150: Patrilineal segmentary systems and the post‑Neolithic Y‑chromosome bottleneck

In this episode of PaperCast Base by Base, we explore a Nature Communications study that proposes a peaceful, socio‑cultural explanation for the sharp decline in male effective population size observed 3,000–5,000 years ago. Instead of widespread violence, the authors show that the dynamics of patrilineal segmentary systems—where lineages split and reproductive success varies between descent groups—can alone generate the Y‑chromosome bottleneck while female lineages continue to expand.

Study Highlights:
The team builds forward‑time simulations of villages structured by patrilocal residence and patrilineal descent, calibrating Y‑chromosome and mtDNA mutation rates and tracking effective population sizes over 100+ generations. They compare scenarios with random versus lineal fission of descent groups and incorporate empirically grounded variance in reproductive success between groups, with and without modeled violence. Lineal fission combined with inter‑group variance in reproductive success consistently produces a strong reduction in male effective population size, whereas violence alone or random fission has a much weaker effect. Bayesian skyline plots from simulated data reproduce a male‑specific bottleneck alongside continued growth of female effective size, and the timing aligns with post‑Neolithic shifts as agro‑pastoralism and patrilineal inheritance spread. Sensitivity analyses show the bottleneck strengthens as variance in reproductive success increases, while female‑to‑male Ne ratios can reach values comparable to those inferred from real data.

Conclusion:
A shift toward patrilineal, segmentary social organization with lineal fission and unequal reproductive success between descent groups may be sufficient to explain the post‑Neolithic Y‑chromosome bottleneck without invoking pervasive warfare.

Reference:
Guyon L, Guez J, Toupance B, Heyer E, Chaix R. Patrilineal segmentary systems provide a peaceful explanation for the post‑Neolithic Y‑chromosome bottleneck. Nature Communications. 2024;15:3243. https://doi.org/10.1038/s41467-024-47618-5

License:
This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/

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