Question: do genes affect your behaviour

Kevin O'Dell answered on 20 Jun 2014:

Excellent question, and perfectly worded. It’s all about whether or how genes AFFECT behaviour (which they do), rather than CONTROL behaviour (which they don’t).

I’ve stalled on answering this, because it’s a really complex question. In fact people have written books about this. But I’ll try to keep my answer a bit shorter.

Firstly let’s thing about something complex that is not behaviour, and then answer your question more directly. We would all agree that there is variation in the height of people. Some people are tall, some short and most somewhere in the middle. It’s also true to say that men are taller than women, though we know that what we really mean is that average man is taller than average woman. There are small men and tall women.

Why are you the height you are? Variation (different alleles) at many genes contribute to your height, so at birth your genetic make-up (2 sets of 25000 genes) will mean that all things being equal you’ll be Xcm tall. However, lots of environmental factors (especially diet, but other things too) can alter this up or down. Variation at most genes contribute a tiny amount to your height (up and down from average) and a few genes have profound effects. These genes include those involved in producing or recognising growth hormone. Individuals that have a mutation meaning they cannot produce or recognise growth hormone will have the inherited genetic condition of dwarfism (you might want to look up achrondroplasia).

Now let us consider a behaviour, such as aggression. Some people are relatively aggressive, some relatively passive and most somewhere in the middle. It’s also true to say that men are more aggressive than women, though we know that what we really mean is that average man is more aggressive than average woman. There are passive men and aggressive women.

Why are you as aggressive/passive as you are? Variation (different alleles) at many genes contribute to your aggression, so at birth your genetic make-up (2 sets of 25000 genes) will mean that all things being equal you’ll have a particular level of aggression. However, lots of environmental factors (everything you experience at home, at school, on-line and everywhere else) can alter this up or down. Variation at most genes contribute a tiny amount to your aggressive state (up and down from average) and a few genes have profound effects. These genes include those involved in helping you control the level of adrenaline in your body. When you’re in a scary situation your body reacts with the ‘fight or flight’ response, which in part involves making a lot of adrenaline. A key point is that you need to calm down afterwards by making the ‘calming-down’ chemical monoamine oxidase (MAO). Individuals that have a mutation meaning they cannot produce MAO will have the inherited genetic condition of ‘inapprorpriate aggression’.

What I would stress is that generally the effect of the environment on behaviour such as aggression is much much greater than the effect of environment on many physical conditions such as height.

So you are correct. Genes do affect behaviour. But environment is nearly always more important.