Here's an opinion piece that looks at how women view other women's breasts:
Do you think she's right, and women are more to blame for the concept of the "ideal breasts"?
And is it more themselves, or other women? Here's a view that thinks it's more about women wanting to look good for other women:
Interesting thought in that one - that teenage girls are not just comparing themselves to other women, but to the boy-band crushes they first fall for. The hot high-school boys are always skinnier than girls, and they're what the girls think of as really attractive. Do teenage girls who want to be attractive also want to resemble boys at the same time (albeit with breasts and much better hair to show off)?
And if so, does this desire form the basis for the rest of their lives, despite the fact that women find appearance less important in men (body appearance, that is - clothing and style still rate high, or even higher) as they grow older?
In a world without men (ignoring all sex issues for the moment), would all women be "fat and happy" has has been suggested? Would this be because there would be no thin men as objects of desire? Or would women still want to show off for each other, and still compete to be less flabby and more beautiful than the others?