Dear 100 Hour Board,
What makes mammaries and buttocks so attractive? I mean, really though.
-[Reader Name Changed]
The answer seems to boil down to biology--it seems that large breasts and buttocks are generally symbols that a woman is fertile, which men are naturally inclined to find attractive.
In researching this question, I also found this article, which suggests that a male fixation with breasts can be highly cultural, not necessarily solely driven by biology. It discusses how some cultures have a very sexualized view of breasts, which men are confronted with from a young age, which can afford another explanation for the male fascination.
This article from Psychology Today suggests that the fatty tissue in breasts has nothing to do with breastfeeding, but instead developed around the time that man began to stand upright, at which point his sexual focus shifted upwards from the buttocks to the breasts.
Since I've graduated and unfortunately lack access to the stellar academic archives of BYU, I haven't been able to find any evidence from reputable sources regarding the fixation with buttocks, but I did come across several theories. I can't speak for their scientific accuracy, but they seemed plausible enough for me to include them.
One is that, similarly to the biological drive behind attraction to breasts, large hips and buttocks are signs of high fertility among women. Another theory is that the buttocks relate to the curvature of the spine, which affects a woman's ability to have multiple pregnancies without injury. Lastly, I read a theory that the attraction dates far back in evolutionary history, to before humans had sex face-to-face, because the buttocks were mainly what men looked at when mating.