The absent bio-dad hypothesis sounds like it would be fraught with confounding variables.
Agreed, but it does sound like a viable biological response.
Well, it’s certainly true that cow’s milk is not as close in nutrients and other general make-up than human milk. But then, it’s not clear that mammals are supposed to drink their own species’ milk past infancy/childhood, so how well another species’ milk “matches up” may be a moot point.
Ass and goat milk is closer to human milk than cow’s milk. But it’s hard to milk an ass. I’m not sure why goats aren’t the predominant source of milk–I know they produce less, but so do they eat and crap less, so I’d think the economics of it would work out the same. Apparently not so.