Hybrid speciation in Galápagos finches

Why Evolution Is True

I’ll take “speciation” in this post, as do all the authors involved, to mean “the origin of reproductive barriers between populations that live in the same area, preventing them from either cross0mating or producing fertile hybrids if they do.” Most biologists think that speciation—the acquisition of these barriers—requires a prolonged period of geographical isolation between populations, allowing them to diverge through natural selection or genetic drift without contamination of genes between the groups. When that differentiation has proceeded to a certain point, reproductive barriers can arise as a byproduct of evolutionary divergence, and thus have new species. (If we’re to be sure they are genuine “biological species”, they should be able to coexist after coming back together in the same area, or, in a one-way test, produce sterile or inviable hybrids when forcibly mated in zoos. If they’re cross-fertile in zoos, we can’t tell, for lots of animals who coexist…

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