One great indication of just how complex the human brain is is how effortlessly we can hold in our minds two thoughts that are directly contradictory. We can fully understand that we hate a TV show and yet somehow willingly sit down to watch all of it. We can be pissed off at not being invited to things we didn’t want to go to anyway. We can be incredibly turned on by something and still find it super gross. That latter one might be on purpose, some scientists are suggesting. (Of course, by “on purpose” I mean completely by accident, like all evolution, but it still serves a purpose.)

In a paper published in Philosophical Transactions of the Royal Society, authors Micheal de Barra and Val Curtis posit that our disgust reactions correspond to “behavioural tasks involved in avoiding disease“, which happens to encapsulate feeling a bit queasy about boning down, it seems.

In the paper, the authors say they are building off previous research which has shown that a whole lot of animals have developed behaviours that help in avoiding sources of infection in their environments as a result of natural selection. They also mention research from 2012 which suggested that even just experience disgust causes our body to up its immune system response.

After surveying around 2,700 they measured a significant disgust response to what they term “promiscuous sexual practices” in the paper, although they don’t quite define what that is. They list promiscuity and “prostitution” as the two sex-related cues that elicit the disgust response – which they describe as things that have historically been indicative of a possible vector for disease and infection.

They also measured responses against things like lesions, signs indicative of bad hygiene, and “atypical appearances“, all of which have generally been signs of the possible spread of parasites or pathogens.

You can read the whole study here if you’re ready to hunker down for some scientific reading.