>>12256572This.
Also there's an evolutionary reason too. The way chromosomes are distributed during meiosis results in one sex chromosome per gamete. If you get too many or too few sex chromosomes it can result in genetic disorders and infertility. As sperm cells can only normally have either one x or y with equal chance of either, this will always result in a 50/50 male to female ratio.
This is very unlikely to change as this process is fundimental to the production of healthy offspring, and mutations in genes responsible would likely be lethal (or cause infertility) so would not be passed on. Even if a mutation or series of mutations arose that allowed a parent to produce more female offspring, this has no immediate advantage for those that have this mutation so it wouldn't be likely that this would be selected for. Not to mention, humans are monogamous so one male to each female is actually an advantage to us.
