[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...