This is an interesting study...but one that will get shredded. For a bazillion years (give or take, lol) prior to the "invention" of junk food and/or fast food, most women were all roughly the same size. Primarily because most people were poor, had challenges finding food (hard to get fast deliveries by covered wagon), did much more manual labor, burnt more calories so....body types were more similar. I don't mean in regards to somatotyping (you know, endomorph, ectomorph, mesomorph) but due to the masses having similar lives.
Second point...what do they consider an "average" sized ass these days? In order to stipulate that those women with higher levels of adipose on their hips and butt (assipose?) they first have to establish what level of corpulence is "above" average. An average sized American woman is in all likelihood going to have more booty than an emaciated person from some poor 3rd world country. But that does not mean the American is smarter or healthier in all cases. We always read and hear stories about people in Japan, those that eat a Mediterranean diet and other examples living longer than most...and I'm going to call nonsense on the "smarter" conclusion as well. I could be wrong though, because I am thin so that must make me...."morder bigly stupider" . :)