A few hundred thousand years ago, a group of fish in an African lake evolved something new—a set of strong chewing jaws in their throats. They became better at eating a wide variety of tough foods. They thrived. They diversified into endless forms most wonderful. And in doing so, some of them doomed themselves.

But the trouble with evolution is that you have no ideas where those doors will lead. You could end up in paradise, or in a one-way corridor to a crematorium.

The cichlid fish (pronounced “sick-lids”) exemplify this lesson. They are icons of evolution. In the limited confines of East Africa’s Great Lakes—Victoria, Malawi, and Tanganyika—the cichlids have diversified into a staggering number of species in a very