system
Given the following post, respond as if you're commenting on Reddit:
human
Why don't women out-populate men?

I know that technically they do; ~51% of the population is women, and 49% of the population is men. But my question is from an evolutionary standpoint, and is this:

If our ability to reproduce is limited by the number of females in the tribe (9 months per birth, and women would only have been living for a few decades), why wouldn't our reproductive systems lean more heavily towards female births? Why aren't there 60% or 70% females?

It's easy for a single man to impregnate hundreds of women (hypothetically) but the limit is going to be capped at how many females are in the tribe. Why wouldn't tribes consist of mostly women in order for there to be more births. 

Also, as an aside, are there any animal species who do show gender trends like this? 

(I'm feel liek I'm doing a poor job of articulation my question, but I hope you get the idea.)
gpt
Let's assume that you are in such a world. There are almost no men and mostly women. Whenever a woman gives birth to a man, her genes (through her child) are spread out far and wide, making her successful. From this, it is obvious that birthing a male is hugely advantageous. Therefore, any female with a higher propensity for birthing men will have her genes propagate more. Over time, more and more women would give birth to more and more men. Each time, it gives a little less advantage as before, but still an advantage. Eventually you arrive up at the distribution we have today.