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Jan8-11, 04:13 AM
P: 630
Quote Quote by LURCH View Post
That's actually a pretty fascinating field of research. The advantage of the last male has alot to do with the shape of the human penis (a fact only recently discovered, I believe). But the amount of advantage is as much a matter of psychology as physiology. It has long been known that these two factors are perhaps more closely related in the reproductive system than anywhere else. If, for example, a husband believes that his wife may be cheating on him, the composition of his ejaculation can actually be changed by that idea. He will still produce sperm of the usual type we all know and love, the type designed to empregnate (call it "reproductive sperm"). But he will also produce "spermicidal sperm", which act to prevent empregnation by another male. These spermicidal sperm come in two basic kinds; an active and a passive kind.

Passive spermicidal spermatizoa swim a certain distance and then stop, looping their flagela into a form resembling a fishing hook. Millions of these become entangled by each other's tails, forming a berrier. The active veriant swim about bumping into others. If the other sperm they bump into does not match the chemical signature of the husband, they attack and kill it chemically, then continue on searching for more. These are the wto types I know of, there may be more.

It's real warfare in there!
Do you have research papers pointing to this specific type of sperm competition in humans ? Including for the claim that expression of certain genes governing type of sperms is regulated by a nebulous stress response to "my wife is cheating on me" ?

It makes no sense to have this type of sperm competition selectively triggered on and off in humans.

Humans are half way between tournament species and pair bonding ones, females are not strictly monogamous, and more importantly, nor are men, so the mechanism to evolve (should it exist) would be most likely not triggered by a stress response, but active all the time.