Eli5: Why in most mammals the female is smaller than the male?

Question

Eli5: Why in most mammals the female is smaller than the male?

In: 1

Answer 1

Sexual dimorphism: distinct difference in size or appearance between the sexes of an animal in addition to difference between the sexual organs themselves.

This isn’t an assured thing in all species, but if it exists in a species it’s because the previous generation(s) lived long enough to procreate and pass on those genes

Edit: dimorphism is the phenomenon, but successfully passing on genes is the reason the phenomenon persists

Answer 2

Males typically fight other males for superiority and then mate with the females. Bigger the male better chance to win.