Cutting edge

Studies show a high degree of heritability in twins' behaviours and feelings of wellbeing. Despite that, we can still direct our lives.

We have been studying twins at the University of Minnesota since 1970 because any psychological research turns out to be more interesting if you do it with twins rather than white rats or college sophomores.

The celebrated study, by my colleague Tom Bouchard, of twins separated in infancy and reared apart has turned up many surprising and provocative findings, and we have replicated and extended many of these results on large samples of twins reared together. We have shown with adult twins that risk of divorce is strongly genetic in origin, while whom you fall in love with is not determined by genes or life experiences - romantic infatuation seems to work like imprinting in baby geese.

Another finding was that 69 pairs of identical twins, reared from infancy without knowing of each other's existence, had very similar scores on a self-report scale that measures subjective wellbeing or happiness. We proceeded to measure happiness levels in some 700 pairs of middle-aged identical twins reared together and got very similar results.

Happiness is not a constant - it varies from time to time. Events experienced within recent weeks can raise or lower one's sense of wellbeing relative to its "set-point", or typical value. However, if the interval is six months or more, even marked highs or lows will have dissipated. This is undoubtedly why well-being is only negligibly correlated with income, social status, marital status and the like. As Jeremy Bentham pointed out almost two centuries ago, "Nature has placed mankind under the government of two sovereign masters, pain and pleasure." But if either the pain or the pleasure were to endure, we should just sit immobile, either paralysed by gloom or entranced in beatitude.

If happiness varies over time about a set-point that is characteristic of the individual then, of course, it is this set-point that must reflect genetic influences. When we re-tested 130 identical pairs nine years after their first testing, we found we could predict Twin A's score now from Twin B's score then as well as we could from Twin A's own score nine years earlier. This would suggest that the heritability of the happiness set-point is nearly 100 per cent.

But I do not believe that the high heritability of the happiness set-point indicates that our average subjective wellbeing is determined just by the level of some neurotransmitter that was set by the genetic lottery at birth. The principal way in which the genes affect the mind is indirectly, by influencing the kinds of experiences we have and by influencing the kinds of environments we seek and the sorts of things we do. If we let our personal genetic steersman have his way, we shall tend to follow a course laid down for us in our DNA. But if much of what is inherited consists of behaviour tendencies that can be resisted, modified and shaped, there is a real possibility for intervention, for countermanding the genetic steersman.

Ours is the only species that gets satisfaction out of making things, and we are the species that is most able to enjoy cultivating and exercising skills. If you examine your life, I think you will find that the most dependable and consistent sources of wellbeing consist of opportunities to gratify your human motivation, doing something useful and doing it well. I believe that a person whose only sources of pleasure were food, sex and television would not score high on the well-being scale.

We can continue following the path laid out by our grandparents or we can change direction, at least to some extent. The conclusion

I come to is much the same as our grandmothers used to preach: happy is as happy does.

David Lykken is in the department of psychology, University of Minnesota, United States.