[JoeAltmaier]

Many animal populations have non-reproductive members. It takes a village to raise a child. In such an extremely social animal as Homo Sapiens, many of our adaptations are social. E.g. it only takes a few men to guarantee another generation, yet 50% men are born in each. Another: we don't die the instant we give birth; we're there (and non-reproductive) for decades afterward, competing for resources. Its the social benefits that allow for this.

[makomk]

There's something called Fisher's principle that explains why the sex ratio of most species is 50:50. In short, if less than 50% of humans are men, then men must have more children on average than women and it becomes reproductively advantageous to have more make kids in order to take advantage of it.

[JoeAltmaier]

Still, in many animal populations the ratio 1:1 doesn't hold. Something else is going on then.

[internaut]

I think it's not quite 1:1 in humans, the males have a slight lead.

http://www.scientificamerican.com/article/is-a-pregnant-woma...