Is there a gene that promotes risk? asks David King
Are you a risk taker? Do you do things "just for kicks"? As a THES reader, perhaps not, but if you do, part of the reason may be genetic.
Before you turn away disgusted at such simplistic "neurogenetic determinism", consider the evidence. In a recent issue of the journal Nature Genetics, two independent groups of scientists report on a link between possession of a particular variant of a gene called D4DR and high scores for a personality trait known as "novelty seeking". This is the first report to identify a particular gene involved in a normal personality trait.
The gene in question codes for the D4 dopamine receptor, a protein which is found on the surface of nerve cells and causes cell changes when it binds the chemical dopamine. Other evidence links dopamine to aspects of behaviour, and physiological differences have been found between the different forms of the receptor. From twin studies, "novelty seeking" is estimated to be 30 to 60 per cent heritable; the variation in the D4DR gene contributes about 10 per cent of the total genetic variation between people. D4DR is not the whole story. Nonetheless, the discovery raises interesting questions.
What does it mean to say that "novelty seeking" is partly genetically determined? The Achilles heel of such research is not the genetics but the psychology. "Novelty seeking" is one of four supposedly "basic" aspects of temperament (the other three being "harm avoidance", "reward dependence" and "persistence") extracted from answers to the Tridimensional Personality Questionnaire, invented by C. Cloninger. These traits are hypothesised to be "based on distinct neurochemical and behavioural substrates", and Cloninger states that "temperament has a simple genetic architecture".
Yet Jonathan Benjamin of Ben Gurion University, Israel, first author of one of the papers, is not so sure. "All of us have reservations about the instruments we use to assess personality. We don't have a good idea of what it is we're assessing." Critics like David Nightingale, psychology lecturer at the Bolton Institute of Higher Education go further. "Personality is not an attribute which attaches to individuals; it's about being part of a society. We can't talk about 'fundamental' aspects of human personality, because in different cultures people have entirely different ways of thinking about people."
"Novelty seeking" is certainly poorly defined. High scorers are said to be "impulsive, exploratory, fickle, excitable, quick-tempered and extravagant". According to Benjamin, the TPQ measures "something . . . telling a bit of a fib, running up an overdraft, being a little bit restless, taking a chance . . . if we wrote down all 16 statements (in the questionnaire), most people would sort of know what we're talking about". This seems more like anecdote than science, yet as Benjamin says, something correlates with the D4DR variations.
Although "novelty seeking" is defined as part of the "normal" personality some people regard it as undesirable. Benjamin says he finds it unattractive.
The science of behavioural genetics, having been in the political doghouse for years, is making a sophisticated comeback. Perhaps the most important impact of such discoveries is to force us to revisit the debates about people and society, nature and nurture. Do people simply "behave", or is there space for free will and decision-making? Can we talk in terms of personality as a fixed characteristic throughout life?
However sceptical we may be, the Tridimensional Personality Questionnaire does seem to measure something which appears to have a biological correlate. The task is to produce a theory to accommodate such information without succumbing to genetic or environmental determinism.
David King is editor of GenEthics News.