Why are males and females 50%-50%?

[Cleita]

14. My theory is that it only became important to have sons when we became

farmers, which lead to territorial wars, which meant we needed extra sons to send into battle to die in protecting our land. I believe this also became the start of the practice of polygamy in our society as a means of taking care of the extra women, who also were needed to breed more sons.

Of course the study of modern aboriginal societies doesn't always hold this as true as the environment and level of development towards our type of civilization seems to dictate both the rules of taking mates and which children from those unions will be the most important.

In modern societies, like the Chinese favoring of sons, it seems to be because they have forgotten over the millennia as to why this is important to them and it has become cultural phenomena.