Evolution is an inherently competitive process: The faster lion catches more prey than other lions, produces more offspring than other lions, and thus raises the proportion of fast lions in the next generation. This couldn’t happen if there were no competition for resources. If lion food existed in unlimited supply, the faster lions would have no advantage over the slower ones, and the next generation of lions would be, on average, no faster than the last generation. No competition, no evolution by natural selection.

— Joshua D. Greene, Moral Tribes