Are there biological counter-balances that accompany larger penises? Humans are one of the few animals without a bone in the penis so an erection requires blood vessels to be filled. With penises which have volumes twice the 2X+ of average ones, much more blood is required. I guess this must affect duration of erections significantly. I have seen videos where some (Castro, Jack Napier) rarely get fully hard at all. How many of you notice any differences? If there are no counter-balances, I guess people have simply breed the minimum length necessary to reproduce. If there are significant counter-balances, which would you prefer: size or duration? If the counter-balances are insignificant, and people breed for altruistic reasons rather than egoistic, I guess we will all have large penises in the future.