Journal of a Cosmic Anthropologist

Substitute any disturbance for El Niño, including those linked to human activity, and we have a way to think about other hybrids, like the coywolves or grolar bears or, in fact, ourselves. Some argue that Homo sapiens left Africa when its northern deserts were passable — that is, at a moment when the climate changed. We bumped into long-lost relatives in Eurasia, the equivalent of today’s polar bears in the grolar bears’ story, and mated.

We may, in turn, have adapted to Eurasian conditions by borrowing genes from these “locals.” Everyone except sub-Saharan Africans carry a small quantity of Neanderthal DNA that includes traits possibly important for survival in Eurasian environments — immune-system and skin-pigmentation genes, among others. And our current genome warehouses DNA from archaic humans that have otherwise disappeared. A recent study estimated that, in the same way that coywolves can be said to store wolf DNA that might have otherwise vanished from the Northeast, one-fifth of the Neanderthal genome endures, dispersed throughout humanity.