Now that I've finally stopped laughing....
I'm halfway through a book called
Bitch: A Revolutionary Guide to Sex, Evolution and the Female Animal, which discusses mating strategies by female animals and how that affects their ability to maximize the well-being of their offspring. The author also discusses how that affects male strategies for reproduction. Apparently male testicle size correlates with how much competition there is to copulate with a female. Gorillas, for instance, have small testicles (in % of body size) because a male gorilla has easy access to a harem of females and doesn't have to work so hard to insure his genes are passed on. Male chimps, on the other hand, have huge testicles (again, in % of body size) because females are sexually aggressive and mate with as many males as they can seduce. In order to insure reproductive success, male chimps have to try harder and more often. lol