I’m not aware of any other species sexually selecting for mammary size. Some birds do a puffy chest thing.

It might be a learned association rather than anything instinctive about tiddies. There’s this one study where they gave rats a backpack fetish, but it has a sad ending because then they murdered all the rats. They did phrase the murder like they were doing a Satanic ritual though, and that kind of took some of the murdery edge off it for me.

I’ve been looking forward to like 20 years from now when all the incels will be into girls with too many fingers.