Re: Breast Size (Was: Re: Homosexuality and genetic determinism)
Bryant (mycol1@unm.edu)
13 Jun 1995 17:21:46 -0600
Gerold Firl <geroldf@sdd.hp.com> wrote:
>>In article <3ri9tc$ru5@auriga.unm.edu> mycol1@unm.edu (Bryant) writes:
>>
>>>Such sperm morphs only appear in species in which male sperm often
>>>co-mingles in females.
>>
>>I've never heard of kamikazi sperm; what is their function?
>
They locate and glob on to non-self sperm. They sabotauge other males'
sperm. My thinking (informed by Baker and Bellis' new book, Human Sperm
Competition) is that this suggests that females in our evolutionary
history mated with multiple males often enough that our sperm is adapted
to compete directly.
Other critters (some small mammals, and mayflies) have appendages on
their peni that actually "scoop out" previous males' sperm while copulating.
Another strategy (employed by snakes and rodents and various arthropods)
is to cap off a male ejaculation with a "glue" that creates a
post-copulatory plug in the female, preventing further mating by
competitors. Ain't evolution grand?
>Another potential advantage of carrying a big stick, especially in a
>co-mingling situation, might occur at the cervix, which is the choke-point
>between vagina and uterus. If the cervix can be stretched sufficiently to
>facilitate sperm transfer to the uterus, then the odds of fertilization
>might be increased for the guy doing the stretching.
>Pure speculation, you understand, but it seems plausible.
That hadn't occured to me. Baker and Bellis published a paper last year
in _Animal Behaviour_ in which they reported that female orgasm enhances
sperm retention by moving the cervix down (if she's on her back), though.
I think this suggests that S.J. Gould and Don Symons were
wrong to declare the female orgasm a "functionless, 'male nipple'"...
Bryant
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