> From: Kate Lyne <kml295@soton.ac.uk>
>
> Females have more control over the
> development of the offspring (they always know who the mother is)
> whereas males need to produce more sperm (and inseminate more females)
> enhance their reproductive success.
Well, strictly speaking, if a male chose well, and could make sure his
mate bore only his offspring, then they would do equally well. But both
the male and the female could improve their chances by cheating: the
male by inseminating other females, and the female, by being
inseminated by a fitter male (as selected by sperm competition).
They both stand to lose from this cheating: the male runs the risk of
rearing genes other than his own, and the female risks losing the
collaboration and resources of the committed male.
> Females will select males on
> commitment to her, on general fitness, and attractivess.
and
> Females
> hide ovulation to have the chance to mate with more males and have the
> choice of the best (fittest) sperm by making the sperm themselves fight
> it out (Sperm wars).
Females, because they are investing
> more in the offspring in terms of energy,
more energy in the offspring,
> The book claims that this is the basis for all human sexual behaviour,
> and that it is mainly driven by unconcious desires. This unconcious
> question is important as it will explain some otherwise "unreasonable"
> behaviour such as adultery.
But one of the things we need to ask ourselves is this: Have Dawkins
and Trivers and Baker just given us another, equally fanciful,
substitute for the Freudian "unconscious," namely, the "Darwinian
unconscious" of ESSs and inclusive fitness?
The material is very interesting, and some of it is surely right, but
remember to be critical. (In any case, the Kitcher book will soon remind
you.)
> (Question: Does a man, at the time of sex, suddenly, after foreplay,
> change the type of sperm he will be using???????)
According to Dawkins, yes! But presumably the sperm production is shaped
not at a particular moment after foreplay, but on the basis of many
factors during the prior 24-48 hours at least (the relevant time window
is at most 8 days).
> Also, why is new sperm best? (Apart from the obvious reason that sperm
> will be younger and less will be dead) Does young ejaculate contain
> more of one type of sperm??
You may be surprised to hear that the female has manufactures her
lifelong quota of eggs before we is born (in some later point in
embryogenesis). Around menarche, those eggs mature one by one, once a
month, until menopause, when ovulation gradually subsides.
The late-life eggs of a woman are indeed old eggs, and more prone to
certain kinds of problems.
With sperms it is different. The male gonad is a sperm factory that only
begins to work around puberty. Spermiogenesis is an active process
that is driven by (1) the amount of sperm that has been manufactured and
stored in the seminal vesicles, and (2) the recency of ejaculation.
Ejaculation empties most of the sperm from the vesicles (it will
vary with circumstances, time of day, partner, amount of foreplay,
etc.). The low levels of the vesicles and the cue from ejaculation
sets spermiogenesis in motion. If there is no ejaculation for over a
month, some of the old sperm are digested and some new sperm is
manufactured, but in general, old ejaculate means old sperm. (Sperm
can live in the vesicles for a few weeks, I believe, and in utero for
about 8 days.)
Yes, newly manufactured sperm are better than old sperm. And of course
there is also the matter of the proportion of killer, rear-guard and
egg-getter sperms. This too can be varied by circumstances, but I think
the cues are much more general than the ones Baker attributes to our
spermiogenetic unconscious! Time, novelty, and excitement are the
modulators of the kind of sperm generated at any time.
One last thing: You may have heard that women can no longer reproduce
after mid-life and the menopause (between 45-55), and their older,
later eggs are more risky than their younger ones. Men, in contrast,
can continue manufacturing sperm until they die. Moreover, men can
continue to manufacture YOUNG sperm till the day they die.
Does that sound unfair? Well there is one other factor I have not heard
discussed but that surely matters: Old men may still be able to
manufacture young sperm, but surely their late-life young sperm are
more risky than their early-life young sperm for the simple reason that
the factory and the manufacturing equipment are, like everything else,
worn with age in older men. The only thing an old male might have going
for him is wealth and power(if he has them). As a consequence, though,
the best strategy for a young woman is to get his resources for the
rearing of her young, but to get the young sired by someone else:
I'm sure old men's young sperm are no match for younger men's young
sperm in sperm competition. So the many plays, stories and operas about
cuckolded old men are on the mark...
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