The case of the Ancient North Eurasians showed that while a tree is a good analogy for the relationships among species — because species rarely interbreed and so like real tree limbs are not expected to grow back together after they branch — it is a dangerous analogy for human populations. The genome revolution has taught us that great mixtures of highly divergent populations have occurred repeatedly. Instead of a tree, a better metaphor may be a trellis, branching and remixing far back into the past.

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