system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How come the world is near enough 50/50 male and female. Is there a reason it isn't 70/30 in either way?
gpt
Imagine that two out of three births were female, and one out of three male. Then the average male would have twice as many descendents as the average female. Therefore, producing more male children would be advantageous. The equilibrium – where it is equally advantageous to have male or female children – is at 50-50. (Unless it requires more resources to produce children of one gender than the other, in which case see nvelex09's post.)