Beauty

http://news.sciencemag.org/brain-behavior/2015/10/why-beauty-eye-beholder

In summary it basically says environmental factors play a lot in the opinion of what's pretty. In a quote from the article:  "They say beauty is in the eye of the beholder. But whether the beholder’s opinion is a product of one's genes or one's environment has long been a question for scientists."

Well I mean, honestly, I'd be hard pressed to imagine all those otakus with body pillow waifus being genetically conditioned to love 2D girls only... :V

It does raise some issues as to whether things like gender preference is really something no one can control, or if its more because of what those persons experienced throughout their lifetime to have such a preference.