Humans split into separate groups for a million years, then merged - David Reich
David Reich discusses genetic research showing that ancestral human populations split into at least two groups over a million years ago, then re-merged several hundred thousand years ago. This population structure and re-mixture event is found across multiple independent studies and is present in all modern human groups, including the Khoisan, though possibly in different proportions.
Summary
David Reich summarizes findings from at least three to five independent genetic studies examining modern human populations. These studies consistently find evidence that is incompatible with a model of a single, homogeneous ancestral human population. Instead, the data points to a population split that occurred well over one million years ago, dividing into at least two — and possibly many more — distinct groups.
After this prolonged period of separation, these groups came back together in a significant re-mixture event on the order of a few hundred thousand years ago. Reich notes that while the specific models differ across the various papers, they all share this core feature: a deep divergence more than a million years ago followed by a coalescence event a few hundred thousand years ago that formed the ancestors of anatomically modern humans.
A follow-up question confirms that this pattern is not limited to a subset of human populations — it is present in all modern human groups, including the Khoisan (one of the most genetically divergent populations alive today). Reich acknowledges that the proportions of ancestry from these ancient merged groups may vary slightly across different modern populations.
Key Insights
- Reich argues that multiple independent studies (at least three, possibly four or five) all converge on the same finding of ancient population structure, strengthening confidence in the result despite differing models.
- Reich claims the ancestral human population split into at least two, possibly many, distinct groups well over one million years ago — far deeper than a simple out-of-Africa bottleneck model would suggest.
- Reich states that a critical re-mixture event occurred on the order of a few hundred thousand years ago, and this merging event is what formed the direct ancestors of anatomically modern humans.
- Reich emphasizes that while individual papers fit different specific models, the shared structural feature — deep split followed by later re-merger — is consistent across all of them.
- Reich confirms that this ancient population structure signal is present in all modern human groups, including the Khoisan, though potentially in slightly different proportions.
Topics
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