Why do human women have some mammal features but not ALL of them?

What I mean is that unlike all other mammals, humans have big brains, don't groom or lick ourselves all day, walk upright, and don't have large breasts in our species. Yet our menstrual cycles, birth patterns, human sex drive, and gestation length are more similar to those of Great Apes, meaning we still have some mammalian features and didn't go all the way, like birds do.<br>Why do you think that is?<br>I think it's because of the pattern of prenatal care and risky childbirth present in all big-brained animals (dolphin, giraffe, rhino, etc). I think our brains are our biggest weakness, because our menstrual cycles, birth patterns, sex drive, and gestation length were affected by it, but I'm not sure.<br>Can anyone please comment?