Why Evolution Is True

by Jerry A. Coyne

When a group of male lions displaces the resident males of a pride, this is often followed by a gruesome slaughter of the unweaned cubs. This behavior is bad for the species since it reduces the total number of lions, increasing their likelihood of extinction. But it’s good for the invading lions, as they can quickly fertilize the females (who come back into estrus when they’re not nursing) and replace the slaughtered cubs with their own offspring. It is easy—though unsettling—to see how a gene causing infanticide would spread at the expense of “nicer” genes, which would have the invading males simply babysit the unrelated cubs. As evolution predicts, we never see adaptations that benefit the species at the expense of the individual—something that we might have expected if organisms were designed by a beneficent creator.