Why do some sexual practices disgust us?

Why do some sexual practices, like incest, cause us to feel disgust? And can our views on what is disgusting change over time?
17 August 2015

Interview with 

Professor Robin Mackenzie, University of Kent


As well as bodily fluids and rotting meat, there are other things people commonly Beetle sexdescribe as disgusting, and many of them are sexual behaviours. But how do we decide what to find disgusting, and what is acceptable? Robin Mackenzie works on Neuroscience, Medical Law & Ethics at the University of Kent, and she explained to Ginny Smith what is going on in the brain when we find something disgusting.

Robin - Well, to start with, the reaction begins in the stomach and actual body as apposed to the brain. So, you get a feeling of discomfort in your stomach. You get tense facial mask skin and you get cardiovascular changes. Your heartbeat goes either up or down. Those sensations get translated by the insular in the brain to other areas of the brain that are involved with an emotional aspect to the reaction and a cognitive reaction. In the prefrontal cortex, we will make decisions about how to deal with the emotions and how to deal with the bodily sensations by interpreting all the information from the different parts of the body.

Ginny - Why are things like sex-related behaviours so strongly linked to disgust?

Robin - Well, one of the current theories which I'm adhering to is that we were evolved to find the best possible reproductive partners that we could what this meant is that we would be in some sense, evolutionarily programmed to look out for people who seem to be healthy, who seem to be likely to be able to produce healthy children with us. So, someone who was ill, someone who was too young or too old, or in other words, unsuitable would arouse disgust to prevent us considering having sex with them as someone in the same kin group as us who was too close to have healthy children with.

Ginny - So, the idea of incest makes you feel disgusted and that's to make sure that you have healthy babies because of course, if you have a baby with someone closely related to you , they can have genetic defects.

Robin - Absolutely.

Ginny - But of course, things have changed a lot since the time we evolved in. So, how does that kind of evolutionary disgust apply in modern society?

Robin - Well, I think this is really interesting because from what Paul was saying, what happens with culture is that there's a lot of repurposing of primaly involved mechanisms. For instance, if we look at reading, reading takes advantage of things in the brain that were setup for facial recognition and object recognition, and those are put together to enable us to read and that's a form of cultural evolution. If we're looking at cultural evolution in terms of sex then with the Judeo-Christian heritage, a lot of the law and a lot of the moral ideas of what was right and wrong, were oriented around ensuring that reproduction took place as a result of sexual activity. So, things like adultery, incest, sex with animals were all seen as very much the wrong thing. Equally, having sex with someone who was menstruating was seen as a very wrong thing. Well, homosexuality and many of the kind of things that were seen as a very bad thing to do and disgusting are now increasingly seen as acceptable as society has become more secular. So, this is a form of cultural evolution.

Ginny - You work in law. What does disgust have to do with the laws that make our country safe?

Robin - Well, if you look at primate societies, there's a lot of evidence to suggest that if punishment doesn't happen to insure that conduct is appropriate in a society, then it's less likely to succeed. This gets harnessed in a form of moral disgust in our society where people think that someone who has misbehaved in a particular way or has behaved in a particular way that they conceive of as misbehaving should be punished. You can see this in terms of various sexual behaviours like paedophilia for instance. It's seen as very wrong, coercive sex and rape is seen as very wrong. So, how this impacts on our legal system is what's prohibited. And also, in terms of the sentencing and punishment, disgust comes in terms of what make the laws in that area and also, what the degree of punishment that's likely to be imposed in the sentencing has been shown to be influenced by individual's differences and in terms of how much disgust they feel.


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