Why has evolution produced a 50:50 sex ratio?

[Gentlygently]

I presume there is some evolutionary reason to why humans (all mammals?) have a 50:50 sex ratio. But what is it? As a species we could probably survive with much fewer men, in a co-operative society. But maybe a race with more men (hence physically stronger) would fight the female dominated race and win?

And yes, male infants are more fragile than females. (I can attest to that in the newborn intensive care!)

Does this explain the "man cold?" I honestly question my husband's ability to tolerate even the slightest bit of pain or discomfort. I can say with 100% certainty, there is no possible way he could have carried, birthed, and fed our children. Zero chance. (That's why I'm confident there will never be such a thing as pregnancy in a man!)

I know that men can produce sperm with a sex ratio different from 50:50 in certain situations (astronauts and deep sea divers I think).

Good luck astronauts and deep sea divers getting laid up/down there...

Sex ratios at birth are the same.

I don't think so? The snakes I was thinking of have can only produce female offspring via parthenogenesis. That would skew the ratio at ... well, birth, I guess, though I am not sure if they give birth or lay eggs.

The opposite happens for bees - worker bees can lay eggs, but as they haven't mated with a male, those eggs produce only males. (Something to do with bee genetics.)

Does this explain the "man cold?" I honestly question my husband's ability to tolerate even the slightest bit of pain or discomfort. I can say with 100% certainty, there is no possible way he could have carried, birthed, and fed our children. Zero chance. (That's why I'm confident there will never be such a thing as pregnancy in a man!)

Oh, I don't know. Pregnancy in a man might happen one time.

After he tells his tale, men will finally believe that it really is painful, and refuse to do it.

I don't think so? The snakes I was thinking of have can only produce female offspring via parthenogenesis.

I’m not sure about snakes, that might have been a bad example - but parthenogenesis isn’t sexual reproduction by definition so isn’t really relevant to the 50:50 ratio that we are discussing.

And while haplodiploidy is fascinating (I used to be obsessed with insects) I think that might take us even further off topic.

It’s frequency dependent selection.

Whatever sex is rarer will be more successful, on average, than the other sex. Thus genes that make more of the rare sex spread. This equalizing the sex ratio.

It’s sometimes called Fishers principle.

george
www.bmj.com/company/newsroom/man-flu-may-be-real/

Man flu is real. Why else would there be man sized tissues?