Dr Claire Hastings introduces the field of Behavioural Genetics ahead of the Royal Institution debate entitled: “The good, the bad, and the genetically predetermined” on the 15th October, during Biology Week 2013.
Your genome contains all the instructions for building you. This includes genes that affect your behaviour: from learning and memory, eating and sleeping or mating behaviour and personality. Within the human population there is variation in these genes, resulting in the behavioural differences we observe in each other. Genes that affect behaviour are a huge part of what makes you, you. They often provide you with more of a sense of self than the genes involved in your physical appearance such as height or eye colour.
So who are you? Are you the simply sum total of your genetic material? Is your behaviour predetermined by your genes? Or is there more to it?
Scientists have been working to answer these questions for over a century. Early research in this field focused on the use of twin and adoption studies to tease apart the role your genes play versus the role of the environment (nature versus nurture) in determining behaviour. This largely revealed that behaviour can be influenced to some extent by the environment. For example, experiencing an increased number of stressful life events has been linked to a higher risk of developing clinical depression.
However, the relationship between behaviour and the environment is more complicated than that. Not everyone who experiences episodes of stress develops depression.
Researchers at King’s College London identified that the serotonin transporter gene, SERT or 5-HTTLPR, is able influence the effects of stressful events on behaviour. There are two variants of the gene, short (S) and long (L). If you inherit even one copy of the short variant (S/S or S/L) then you are more sensitive to the effects of stress than if you possess two copies of the long allele (L/L) (1). Therefore people who possess the short allele are more likely to develop depression in response to stressful life events than those with the short allele. This is not to say that everyone with the short allele will develop depression. Individuals who possess a copy the short allele but have a relatively stress-free life avoid developing depression.
Of course there are other genes that influence depression, and depression is just one example of a behavioural disorder with both a genetic and environmental component. There are many more that are beginning to be uncovered as the field of behavioural genetics advances. Taking this into account, it would be wrong to say that your behaviour is solely determined by the genetic code you were born with. Genes affect how your body reacts to the environment, and the environment affects which genes are expressed.
Our behaviour cannot be predicted by genetics alone; the people and places around you have an equally important part to play in determining your behaviour. I hope this is a comforting thought.
Interested in behavioural genetics? Check out this blog by David Dobbs. It is fantastic.
1) Caspi A, Sugden K, Moffitt TE, et al. Influence of life stress on depression: moderation by a polymorphism in the 5-HTT gene. Science. 2003 Jul 18; 301(5631): 386-389