The explanation I was referring to was in your post.
Yes, this. If there are 300 females for every male, males have better chance of reproducing. Thus favoring male births (and vice versa).
Wikipedia knows it all:
1. Suppose male births are less common than female.
2. A newborn male then has better mating prospects than a newborn female, and therefore can expect to have more offspring.
3. Therefore parents genetically disposed to produce males tend to have more than average numbers of grandchildren born to them.
4. Therefore the genes for male-producing tendencies spread, and male births become more common.
5. As the 1:1 sex ratio is approached, the advantage associated with producing males dies away.
6. The same reasoning holds if females are substituted for males throughout. Therefore 1:1 is the equilibrium ratio.
This tells us "You would expect it to balance out so that there is a 1:1 ratio of male and female babies". But it doesn't explain why there'd be more male fetuses.
Add in the information that more male fetuses die and it makes more sense: in order to achieve a 1:1 gender ratio
at birth you'd need more male fetuses.
I guess technically you'd want to factor in child mortality too, but I'm not aware of any gender difference there and it doesn't change the basic idea.
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Topic: Monogamy? (Read 6391 times)