Why are they attracted to other women?
I use scare quotes because they’re really bisexual, not that there’s anything wrong with that. Most women who “become” lesbians later in life for various reasons (like having a lot of bad experiences with men) were always bisexual, because it makes evolutionary sense for them to be. It also explains “LUG”s (lesbian until graduation).
I would go beyond the thesis here and note that women compete with other women on their looks, so they’re actually pretty finely attuned to the attractiveness of other women.
So male proto-humans developed sexual dimorphism (with males being bigger and stronger) in order to build bigger harems? Could be, I suppose. The article didn’t conjecture that female proto-humans developed bigger boobs to trick the alpha males into thinking they were pregnant and so shouldn’t be abandoned for a younger female. It would have provided some support for their conjecture if they had mentioned if girl-on-girl chimp sex was a thing.
I was reading an article several years ago about a modern man spending quite some time with a stone-age hunter-gatherer tribe. That tribe, at least, didn’t seem to have much in the way of a harem culture–instead, they paired off every night and swapped partners when they felt like it. I have no idea how common that was–I don’t think there are many stone-age tribes around anymore to investigate. I wouldn’t be too surprised if large harems were corelated to agriculture.