This honest recognition of the power of pleasure in the service of evolution by Darwin was edited out of the posthumously-published text, and only restored in 1958. But as my quotations illustrate, Darwin, like Smith and Spencer, clearly recognized that pleasure is one of the primary mechanisms by which our biology affects our behaviour—along with its antithesis, pain. No wonder orgasm is so pleasurable: it is the ultimate life-supporting act—or at least, it is from your genes’ point of view! Translated into the new thinking of the diametric model of cognition, you could say that feelings of pleasure and happiness are the motivating, mentalistic expressions of this basic genetic mechanism.
However, new research by Jan-Emmanuel De Neve, James Fowler, and Bruno Frey has found that the default setting for happiness is directly controlled by a single gene. Twin studies have already established that baseline happiness is heritable but, using data from the National Longitudinal Study of Adolescent Health, these authors show that individuals with a more efficient version of the serotonin transporter gene, 5HTT, are significantly more likely to report higher levels of life satisfaction. Having one or two versions of the more efficient gene raises the average likelihood of being very satisfied with one's life by 8.5% and 17.3%, respectively. This is a direct, linear relationship which, as the authors point out, is not evidence of a gene-environment interaction, but of a direct association between the gene and subjective well-being: double the gene, and the satisfaction doubles with it!
However, the authors add that “It is crucial to point out at the outset that this association study does not establish that 5HTT ‘causes’ happiness, nor does it exclude the possibility that several other genes may play a role, but it does suggest at least one possible causal pathway able to account for the influence of genes on happiness.” And as they also point out, serotonin metabolism in general and 5HTT expression in particular play an important role in mental illness, notably depression and related disorders—just as you would expect if it were critical to feelings of well-being.
In other words, pleasure did not only evolve as a means by which genes could motivate their carriers to act in ways which would reward their DNA’s long-term survival and reproductive success as Smith, Spencer, and Darwin effectively realized. Additionally, this study shows that one particular gene also controls the default setting of the system where long-term feelings of satisfaction are concerned. Modern equivalents of Darwin’s censors will doubtless deploy their formidable mentalistic skills to minimize its immediate impact, but this discovery will bring much pleasure to those of us with a more mechanistic turn of mind—no matter which 5HTT gene we have!