Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: neilep on 05/09/2007 19:52:03
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Dear Girlies and blokeys,
Here is a piccy of a blokey and girly:
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Nice eh ?....notice how happy and equal in numbers they are:
The blokey is on the left and the girly is not !! [;)]
Is the proportion of genders split right down the middle ? 50-50 ?
If not.....why not ?..cos with 6 billion of us you'd think it'll be pretty much spot on !
what about other examples of the animal kingdom ?..fisheys...insects....birdies ?
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I've heard that more males are conceived (lighter Y chromosome allows the sperm to swim faster), but are more likely to miscarry (lack of duplication of some genes on the X chromosome means that more male fetuses are non-viable, same reason as the x-linking of conditions like colour blindness or more seriously haemophilia, with males predominantly affected and females mainly carriers).
Also, men tend to die younger (now that women at least in this country don't often die in childbirth).
So there are more women about, especially at the older end of the population.
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Actually, slightly more boys are born than girls. However as Rosy said, men tend to die younger (and young men tend to die in accidents) so the overall "winner" depends on the demographics. If lots of people in a society live to be old then more members of that society will be female than male. On the other hand, if infant mortallity is high then, in order to maintain the population, the number of young children will be large. This means that the males will outnumber the females.
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I've heard that more males are conceived (lighter Y chromosome allows the sperm to swim faster)
Also, supposedly for the same reason, having sex before ovulation is more likely to have a female child, while having sex precisely timed to ovulation will increase the probability of having a male child (because the male sperm make a quick dash for where the egg should be, but if they get there too early, then they die, but the slower female sperm will have the chance to catch up).
Apparently there is also research to suggest that increased social status will increase the probability of a male child (not only for humans).
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why would that be?
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why would that be?
If you are referring to the social status issue, I believe the argument is that most mammals are polygamous. If one assumes that the male child of an alpha male is more likely to be an alpha male; then it follows that the male child of an alpha male will have greater reproductive success than the male child of a non-alpha male. Since one male might mate with many females, or with no females; thus a successful male could be very successful at reproducing, while an unsuccessful male could be very unsuccessful. By contrast, a female is likely to have fairly limited variance in the success of their reproduction (there is some variance, but far less than there is for males). Thus, if you expect your children will not be alpha males, then it makes more sense to invest in females, who at least have have a fairly constant reproductive success rate than a male who will have an exceptionally low reproductive success rate. On the other hand, if you know your child will probably have a high status (because you have a high status), then it follows that having a male child will allow it to maximise its reproductive success to a greater extent than having a female child.