A nice article. Regarding why people more strongly respond to large breasts, large penises, etc. we need to remember that hardwired instincts aren’t necessarily rate-limited. For example, herring-gull chicks are hardwired to respond to a red blotch on an adult’s beak: they peck the blotch and this triggers the parent to regurgitate fish into the chick’s mouth. But if you present a newly-hatched chick with (i) a false beak with a normal-sized blotch, and (ii) a false beak with an enormous red blotch, the chick will preferentially peck the second option. It simply does a better job of stimulating the hardwired response. As in real life no chick would have to make such a choice, there’s no selection pressure to build in a rate-limit to its instinct.

With humans the picture is a little more complicated: males will tend to prefer large pert breasts over large saggy breasts because pertness is an indicator of youth which in turn is an indicator of fertility. So it’s not just about size, but about a confluence of factors. And with all large-brained animals there’s variegation to ensure that instead of every member of the group wanting precisely the same thing there’s a spread of desires to minimize over-utilization of a scarce resource. This is why a family of otters will show preference for different types of food: one may adore abalone while another prefers squid, for example.

As for anal sex, it’s interesting to note that other primates enjoy the same pleasure. Bonobos regularly indulge, and chimps have been observed likewise enjoying anal play. We are far less different from our primate cousins than we often like to think.