Holy shit, I know why women are smaller than men despite our species being the most cooperative mammals on the planet! It’s all in the tits!
Literally. Imagine this scenario. A foraging tribe has a bunch of pregnant or nursing mothers who are all, in their non-tit-engagedstate, on average equal in body mass to the tribe’s males. These women need to consume (a modern recommendation of) 500 more calories per day to maintain their weight while the child develops. That means they would need to consume the ancient equivalent of 2300 to 2800 calories. But, if women weren’t man sized, that total adds up to just 2000-2500 calories — exactly the amount required to maintain a healthy adult male.
Human sexual dimorphism isn’t a result of males needing to bleet and grunt and smash their way to reproductive success at all. That theory contradicts entirely everything else we know about human sexual physiology. The dimorphism is actually a direct result of the fierce egalitarianism of ancient humans. Most adult females were pregnant or nursing at any given time in their lives. Therefore they devoloped smaller bodies in order to match their caloric needs to the men. It isn’t aggression that causes the difference, but cooperation.
Isn’t the world happier for that knowledge?