ps418

Individuals differ from one another in terms of their average levels of subjective well-being. What accounts for these individual differences in well-being (WB)? Surely there are multiplefactors which account for individual differences in WB, including a genetic factor. An interesting study conducted by Lykken and Tellegren shows that 1) there is a strong genetic influence on adult WB (broad heritability of 0.4), 2) that 'shared environmental effects' exert a surprisingly weak influence on adult WB, and 3) that individual differences in education, income, marital status, and 'religious commitment' (as measured by the Traditionalism scale of the MPQ) do not account for much of the individual differences in WB.

That their should be a genetic component to WB is hardly surpising, since neurons and neurotransmitter systems play a profound role in regulating WB, and both are constructed from proteins, which are coded for and regulated by genes, which are polymorphic between individuals (e.g. polymorphisms in serotonin, dopamine, or GABA genes, or in genes that regulate the expression of these genes). Furthermore, a genetic influence on diverse mood disorders in humans is well-established (e.g. Kendler et al., 1995; Rice et al., 2002), and polymorphisms associated with 'anxiety' in mice have been reported (e.g. Crestani et al., 1999). That subjective well-being is somewhat malleable also seems obvious, at least over the short-term.

A general caution about the generalizabilitity of Lykken and Tellegren's heritability estimate is in order as well. All of the twins in Lykken and Tellegren's sample were adults, and it is quite possible that the strength of the genetic influence on happiness changes over time, as is the case for other cognitive and behavioral traits. For instance, the effects of the environment on childhood WB may (or may not) be stronger than for adults. It is also likely that in more extreme circumstances, the 'shared environment' could have a significant effect.

Lykken assessed 4 twin groups using the Well Being scale (WB) of the Multidimensional Personality Questionnaire: a group of MZ twins reared together (MZTs), a group of DZ twins reared together (DZTS), a group of MZ twins reared apart (MZAs), and a group of DZ twins reared apart (DZAs). The test was repeated ten years later for a subset of 254 twins. The results were consistent for both sets of MZ and DZ twins. Whether seperated in infancy and reared apart, or reared together in the same home, MZ twins WB scores are strongly correlated (r=0.44 and r=0.52, respectively), while DZs are not correlated any more than two people picked at random, whether reared apart or together (r=0.08 and r=0.02, respectively). That the DZT and MZT correlations are identical, within error, to those for DZAs and MZAs indicates a general lack of 'shared environmental influences' on WB (within the range of environments sampled). Being reared together, in the same homes with the same parents, apparently does not make people similar with respect to their adult WB.

Income, educational attainment, marital status, and one measure of religious commitment, on the other hand, explained at most a few percent (3%) of the variation in well-being as assessed with the MPQ scale. Perhaps suprisingly, the WB of you identical twin is by far the best known predictor of your own subjective well-being, even if you were seperated from that twin in infancy and reared seperately. Yet the subjective well being of your fraternal twin, even if you were raised with him or her, is not at all predictive of subjective well-being. This is strong evidence, by the way, for a 'nonadditive genetic influence' on WB.

Lykken, D., and Tellegen, A., 1996. Happiness Is a Stochastic Phenomenon. Psychological Science 7(3).

See also the commentary by Dean Hamer, which appeared in Nature Genetics: Hamer, D., 1996. The heritability of happiness. Nature Genetics 14, pp. 125-126. PDF file

And a more recent article covering the same general topic by behavior geneticist David Rowe:

Rowe, D.C., 2001. Do people make environments or do environments make people? Annals of the New York Academy of Sciences 935, pp. 62-74.

References

Crestani et al., 1999. Decreased GABAa-receptor clustering results in enhanced anxiety and a bias for threat cues. Nature Neuoscience 9, pp 833 - 839.

Kendler et al., 1995. The structure of the genetic and environmental risk factors for six major psychiatric disorders in women. Phobia, generalized anxiety disorder, panic disorder, bulimia, major depression, and alcoholism. Arch Gen Psychiatry 52(5), pp. 374-83.

Rice et al., 2002. Assessing the effects of age, sex and shared environment on the genetic aetiology of depression in childhood and adolescence. Journal of Child Psychololgy and Psychiatry 43(8), pp.1039-5.

Jesse

I imagine part of the complexity here is that even if you and your twin are raised separately, your environments are more likely to converge than for a fraternal twin raised separately, because your personality and choices effect your environment; for example, if I am married, that may make it more likely that my identical twin is also married, if I am shunned by my peers that may make it more likely my identical twin has had a similar experience, if I have a high income that may make it more likely my identical twin does too, etc.

pz

Oh, good grief. Not more of this ideologically-driven Minnesota twins crap.

cricket

<grabs a bag of popcorn; takes a seat in the bleachers>

Friar Bellows

Can I join you there? It would make me happy.

ps418

Thank you for your kind, patient, factual and thorough analysis of my post. When it comes to twin studies and genetic influences on behavior and cognition, I have come to expect such high-quality dialogue from you.

Patrick

ps418

Yes, the correlation is probably partially mediated by broader personality traits, some of which also have substantial heritability (see Bouchard and McGue, 2003 for an excellent review).

pz

Yes, and I've learned that you are extremely credulous when it comes to studies that seem to support your bias, no matter how shoddily done they are, so you shouldn't expect much dialogue from me. There isn't much point.

ps418

That's precisely the response I expected from you: accusations of bias and name-calling against me personally. Thanks again Pz.

ps418

For those who are interested, there's a great review article on twin studies available for free from Nature Reviews Genetics. The article reviews the classic twin study designs and what they have shown regarding genetic and environmental influences on all sorts of traits, as well as new twin study designs including parents, siblings and spouses, improvements in analytic techniques, development of many new twin registers worldwide, and other topics.


Boomsma, D., Busjahn, A., and Peltonen, L., 2002. Classical twin studies and beyond. Nature Reviews Genetics 3, pp. 872-882.