Biologists not infrequently find ourselves speculating in a purely intellectual way about things that are otherwise not discussed in polite company. Take feces for example. The discussion of feces is so stigmatized as to have its very own adjective. Scatological humor is humor relating to poo. If one's conversation, thinking, humor or complexion is described as scatological, one is generally not flattered. But there are legitimate biological questions to ask about poo.
This afternoon, I was considering the question of why we evolved to have our anus placed such that feces, after leaving the rectum, have ample opportunity to contact the surrounding skin, which then need to be cleaned. And then I began trying to imagine other places a human's digestive tract couple potentially end, and what the advantages and disadvantages would be. What would it be like, for instance if our genitals were behind, rather than in front of, our anuses. And, taking a comparative approach, I thought about what I know about the anal anatomy of other species, and how they clean themselves, or avoid the need to do so. And all in a purely intellectual context, without the slightest feelings of revulsion, shame or titillation. Yet somehow, I knew that one is expected to keep that sort of speculation to one self. Unless one is a biologist. And even so, I probably won't bring it up to my neighbor on the train tomorrow.