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John Leonard
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 Posted: Sun Dec 07, 2003 11:41 pm Post subject: Two questions about sex: |
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I have read that the number of males born annually relative to that of the
number of females, in the human population, is approximately a constant of
51/49. Since males are at a greater risk of death this difference might help
promote a more equal distribution at the time of fertility.
My first question is this: how is this proportion maintained? I am at a loss
to understand how it could be maintained except through feedback. If this is
so, by what means does this feedback assert itself? Is it, for instance,
conceivable that we unconsciously modulate the likelihood of male versus
female birth via observations made in our brains?
My second question is this: In lions we see social groups (i.e. prides) in
which females outnumber males by several-to-one. Our species has a more
one-to-one ratio. First, is there a difference in the birth ratios of
females to males between lions and humans? Certainly, a male lion fights
more for the simple opportunity to reproduce than we do. Is there in fact a
difference between the nature of male competition between lions and humans?
Is it that lions compete more for the simple opportunity to reproduce
whereas humans compete more for the most highly prized females?
John Leonard |
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Anon.
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| Posted: Mon Dec 08, 2003 4:53 pm Post subject: Re: Two questions about sex: |
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John Leonard wrote:
[quote]I have read that the number of males born annually relative to that of the
number of females, in the human population, is approximately a constant of
51/49. Since males are at a greater risk of death this difference might help
promote a more equal distribution at the time of fertility.
That was first shown by Laplace in the eighteenth century. He concluded[/quote]
that he was "morally certain" that the sex ratio was less than one half.
[quote]
My first question is this: how is this proportion maintained? I am at a loss
to understand how it could be maintained except through feedback. If this is
so, by what means does this feedback assert itself? Is it, for instance,
conceivable that we unconsciously modulate the likelihood of male versus
female birth via observations made in our brains?
I think there is some evidence that this happens, but over a longer time[/quote]
scale, you will get evolution towards an idea sex ratio, because the
rarer sex is favoured - if there are lots of males, then if you produce
a female, it>s more likely to have a mate, and produce offspring. This
is a classic result, first shown by Fisher over 70 years ago. He showed
that (under his assumptions), you should get an even sex ratio, but it>s
not too difficult to relax these to get a slightly skewed sex ratio, in
essence through the mechanisms you suggested.
Bob
--
Bob O>Hara
Rolf Nevanlinna Institute
P.O. Box 4 (Yliopistonkatu 5)
FIN-00014 University of Helsinki
Finland
Telephone: +358-9-191 23743
Mobile: +358 50 599 0540
Fax: +358-9-191 22 779
WWW: http://www.RNI.Helsinki.FI/~boh/ |
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Tim Tyler
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| Posted: Mon Dec 08, 2003 4:53 pm Post subject: Re: Two questions about sex: |
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John Leonard <jleonard2_but_no_spam@si.rr.com> wrote or quoted:
[quote]I have read that the number of males born annually relative to that of the
number of females, in the human population, is approximately a constant of
51/49. Since males are at a greater risk of death this difference might help
promote a more equal distribution at the time of fertility.
My first question is this: how is this proportion maintained? I am at a loss
to understand how it could be maintained except through feedback. If this is
so, by what means does this feedback assert itself? Is it, for instance,
conceivable that we unconsciously modulate the likelihood of male versus
female birth via observations made in our brains?
[/quote]
The most common hypothesis seems to invokes differences in sperm motility
- largely due to the approx 3% difference in mass between X-bearing and
Y-bearing gametes.
--
__________
|im |yler http://timtyler.org/ tim@tt1lock.org Remove lock to reply. |
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