Competition within a single species is one of the most powerful forces in evolution. Since, as Darwin pointed out, most organisms produce far more offspring than can possibly survive, some organisms will do better than others. And since members of the same species need the same food and shelter, and must mate with each other, not with the members of another species, resources will almost always be limited in some way, and competition will arise. Sometimes this can lead to diversification within a species ­ or even, eventually to speciation ­ as organisms escape from competition by learning to eat new food or by being choosy about their mates.
