Every now and then I’ll hear someone say something like: “This [insert trait here] makes perfect evolutionary sense! It prevents overpopulation!” But it shouldn’t take much thought to realize that this doesn’t make much sense.
Firstly, any given trait of any given animal cannot be said to exist only by having provided an evolutionary advantage to past generations. That is, some traits can be passed on from one generation to the next despite being a burden to the quality of that organism’s life, as long as it does not too greatly hinder the reproduction of the population as a whole.
Secondly, how would overpopulation reduce reproduction of the population as a whole anyway? Overpopulation comes about when the ability to breed is easier than the ability for all members of a population to access needed resources to live long enough to continue breeding. This will prevent the reproduction of some members of the population, but it would not affect the reproduction of the population as a whole. Therefore no evolutionary traits could possibly be passed on to prevent overpopulation. If a trait by itself hinders reproduction, it won’t be passed on. Overpopulation does not hinder the reproduction of the species as a whole — therefore it causes no evolutionary effect in and of itself. (The fight for needed resources may have evolutionary effects if those without the necessary access to the resources die off, but the cause of the scarcity of the resources is irrelevant; it doesn’t matter if the scarcity of a resource is caused by overpopulation, by competition from other populations, or if the resource is just naturally scarce.)
Every population will continue to reproduce until it reaches the limits of its needed resources, or until the limits of the resources change or the population is gobbled up by some other population (or controlled by humans). In this way, you could say it is natural for every population to breed until overpopulation occurs. The only population that can escape this nature is the human population, because we can make the conscious decision to not breed.
So, if you ever find yourself asking: “Hmmm, I wonder why [insert trait here] is passed on from generation to generation even though it does not aid reproduction?” and then find yourself answering: “Oh, to prevent overpopulation!” — please take a moment to consider your lack of logic and amend your thinking ways.