I was in a convenience store today and saw a woman with a perfectly round and plump backside. I start to look around and (it being lunchtime, it’s busy) see every guy in there pretty much stop what they’re doing to take a look at this woman’s ass.
I can understand that the evolutionary purpose of big breasts, this tells the male that the female is capable of carrying a good amount of milk for the youngin. I also have heard that nice hips means she can pop out a good amount of babies with ease.
But why is a nice, round ass attractive to the heterosexual male?
Actually, breasts mimic the backside, which is why they are attractive. The article I read (which had images of both bottom and breast cleavage photographed in such a way that you had no reference points other than the cleavage, to show they did in fact look alike) posited that humans used to mate “doggy style”, so the curve of the bottom was erotic for the male. I am not having any luck finding the article now, I will keep looking.
Actually, I think it relates to child bearing. The hip to butt ratio is critical when it comes to picking a mate that is likely to have success in rearing a child.
As I’ve argued before, there certainly is.
Man is not the only primate in which the female has a buttock-mimic on the chest. The Gelada Baboon has a characteristic “necklace” of blister-like decorations on the chest. These precisely mimic a similar set that ring the buttocks. Furthermore, they become engorged and particularly visible when the female is sexually receptive.
It is, I think, significant that the Gelada tend to approacj for mating face to face (although they mate from behind, “doggy style” , like other apes), and so there’s a reason that such a mating signal appears on the front as well as the back.
In the case of humans, the significant buttocks are unique. Other apes are knuckle-walkers, and the human gluteus maximus, which allows us to walk upright without a counterbalancing tail (the way all other bipeds have done it), is enormous. The human female breast appears to have evolved to mimic this large set of buttocks, which unique to our bunch. Man is the Ape with the Butt, and hence the Ape with Boobs. we are unique.
Large breasts are NOT necessary for milk production. As Morris (and others) have pointed out, most of the breast is fatty tissue, not storage space, and apes do quite well at feeding their young without having a large breast to store milk.
From what I gather, a shapely butt on a male is attractive to women as well.
There’s an inference from this, IMO: The other erogenous-to-view secondary (or primary) sex characteristics are nearly all ventral – “front” in bipedal humanity. But at least 50% of the time, the persons of the opposite sex whom you encounter are standing, sitting, or moving in a direction facing away from you, or if reclining, lying with the delicate parts downward and the relatively more robust back and buttocks upward.
For the buttocks – in either sex – to become attractive in terms of sexual interest means a much higher proportion of male-female casual contacts will lead to courtships and more intimate contacts, than would be the case if only “views from the front” were erogenous.
It could just be that it’s a secondary sex characteristic. A lot of the traits we men find attractive about women are things that are different between the two genders–they tend to have longer, more slender necks; they’ve got longer and narrower hands; and their butts are angled a little differently due to the female pelvis being positioned for childbirth.
As, for that matter, do small-breasted humans. While admittedly a woman’s breasts will grow while nursing, that might turn an A cup into a B cup. There’s still no need for triple-D. Aside, of course, from sexual selection.
Like you said, a certain width of the hips is attractive form an evolutionary point of view because it allows for childbirth. But if the hips are too big, it indicates too much body fat which suggests not being physically fit. So it makes sense that the most attractive butt is going to be neither too big nor too small, and good muscle tone is going to give it a nice round, firm appearance.
It’s possible that there is no evolutionary function at all. You can make up stories for the advantage of anything, but the relationship of attractiveness of a butt to sexual attractive may simply be a small to non-existent effect. How many people with non-shapely butts manage to have children? Most, presumably, and it’s extremely hard to argue that the ones that don’t would have if only their butts were more beautiful.
General attractiveness is certainly a selection advantage. But with humans, the range of what is considered attractive is enormous, covering the vast percentage of the species. In crude terms, you have to be really hideous not to mate. Those who are hideous have more things wrong with them than just a butt, or just any single part. They are hideous in all ways.
I consider this the fallacy of the part. You can’t do regression analysis on human reproduction and say that it’s 42% breasts and 23% face and 11% hair and 9% legs and 7% hips and and 5% feet and 3% buttocks. It doesn’t work that way.
Just call me a Caveman then. 
