the bigger the bollox, the more he frolix.

Animals that 'keep harems' of females tend to have larger sex organs than animals that tend to live in sex seperate groups that only meet once in while when a female is in heat.

Horses keep harems.. elephants don't.

some 4 legged animals have long and bony penises.. (simple to physically get to the female, but harem keeping animals (especially among primates) have large than, well, larger than needed sex organs. (and higher levels of testosterone) in order to show dominance and maintain order (by frequently engaging in sex acts.)

among all primates, if mama ain't happy, ain't nobody happy... and one way to keep mama happy is sex.