Do Genes Determine Mood?

Studies within the last two or three decades have shed light on the pre-determined factors that make us who we are. Though still hotly debated (and perhaps too often overstated) there is increasing evidence that our personality and behavior are influenced, in varying degrees, by our biology. Alterations to our brain chemistry or hormones, whether deliberately or as the result of certain genes, cause subsequent changes to our mood, cognitive ability, and even morality. As unsettling as it may be for many people, it’s possible that a good part of who we are may be genetically predisposed by the vagaries of biology – a complete accident of birth beyond our control.

The Economist had some time ago published an article on this subject, dealing specifically with the most sought after (and perhaps elusive) of all human emotions: happiness. Feeling good is obviously something any normal person would want, and everyone is concerned with living a good and content life. But figuring out what makes us happy, and how to attain it, has been one of the oldest subjects of debate and literature. With the current economic and political problems that are befalling us, and a growing sense of cynicism and anxiety about the future, concerns about living a stress-free and enjoyable life are understandably widespread.

So imagine the implications of discovering that happiness, if not other emotions, has more to do with your genes than with any existential or spiritual search. Consider the following study detailed below:

[The fact that] personality, along with intelligence, is at least partly heritable is becoming increasingly clear; so, presumably, the tendency to be happy or miserable is, to some extent, passed on through DNA. To try to establish just what that extent is, a group of scientists from University College, London; Harvard Medical School; the University of California, San Diego; and the University of Zurich examined over 1,000 pairs of twins from a huge study on the health of American adolescents. In “Genes, Economics and Happiness”, a working paper from the University of Zurich’s Institute for Empirical Research in Economics, they conclude that about a third of the variation in people’s happiness is heritable.That is along the lines of, though a little lower than, previous estimates on the subject.
But while twin studies are useful for establishing the extent to which a characteristic is heritable, they do not finger the particular genes at work. One of the researchers, Jan-Emmanuel De Neve, of University College, London, and the London School of Economics, has tried to do just that, by picking a popular suspect—the gene that encodes the serotonin-transporter protein, a molecule that shuffles a brain messenger called serotonin through cell membranes—and examining how variants of that gene affect levels of happiness.
Serotonin is involved in mood regulation. Serotonin transporters are crucial to this job. The serotonin-transporter gene comes in two functional variants—long and short. The long one produces more transporter-protein molecules than the short one. People have two versions (known as alleles) of each gene, one from each parent. So some have two short alleles, some have two long ones, and the rest have one of each.
The adolescents in Dr De Neve’s study were asked to grade themselves from very satisfied to very dissatisfied. Dr De Neve found that those with one long allele were 8% more likely than those with none to describe themselves as very satisfied; those with two long alleles were 17% more likely.
Correlation doesn’t equal causation, but there still seems to be a strong enough link between these alleles and one’s mood to merit further inspection. Imagine if we could trace other feelings to certain genetic markers as well. Could anger, recklessness, or greed, among other emotions, also be attributed to certain biological factors? What about more severe examples like psychosis? What does all this say about the way we treat certain behavioral or mental problems, both medically and as far as societal attitudes to them?
Imagine altering our genetic code in some way could be the key to solving these kinds of problems. Rather than consult a psychotherapist or take some sort of medication, you’d see a specialist in gene therapy instead. Perhaps even mild cases of the blues could be addressed through some sort of genetic tweaking. Granted, I’m getting way ahead of myself here, but it doesn’t hurt to discuss the possibilities, however unlikely they may currently seem.
In any case, these scenarios are only the beginning. There is another implication from this study that could be even more contentious:
Where the story could become controversial is when the ethnic origins of the volunteers are taken into account. All were Americans, but they were asked to classify themselves by race as well. On average, the Asian Americans in the sample had 0.69 long genes, the black Americans had 1.47 and the white Americans had 1.12.
That result sits comfortably with other studies showing that, on average, Asian countries report lower levels of happiness than their GDP per head would suggest. African countries, however, are all over the place, happiness-wise. But that is not surprising, either. Africa is the most genetically diverse continent, because that is where humanity evolved (Asians, Europeans, Aboriginal Australians and Amerindians are all descended from a few adventurers who left Africa about 60,000 years ago). Black Americans, mostly the descendants of slaves carried away from a few places in West Africa, cannot possibly be representative of the whole continent.
That some populations have more of the long version of the serotonin-transporter gene has been noticed before, though the association has previously been made at a national, rather than a racial, level. In a paper in the Proceedings of the Royal Society, published in 2009, Joan Chiao and Katherine Blizinsky of Northwestern University, in Illinois, found a positive correlation between higher levels of the short version of the gene and mood disorders (China and Japan have lots of both) and with collectivist political systems. Their hypothesis is that cultures prone to anxiety tend towards systems that emphasise social harmony and away from ones that emphasise individuals’ independence of each other.
Obviously, as with most such findings, more work will have to be done to replicate and validate the conclusions. But the suggestions this discovery makes are vast: not only is everyone’s behavior influenced by genes to a significant level, but so are entire societies and political systems by extension. The way we form our communities, govern ourselves, or go about engaging in economic activity can be informed, in part, by the genetic dispositions of the majority of the population. Does that mean that certain nations, like individuals, are destined for certain paths of development? Such a genetically determined fatalism would be understandably concerning and divisive.
As near as we can tell, it would also be an exaggeration. Thus far, most studies have shown that genes, while significant influencers, are not the only determinants of who we are. Being born with a certain genetic predisposition isn’t always destiny. But it’s still something worth keeping in mind. There’s no doubt there will be a lot of debate about this, but there’s one thing that isn’t likely to be disputed:
This latter study may be a few steps too far along the road to genetic determinism for some people. But there is growing interest in the study of happiness, not just among geneticists but also among economists and policymakers dissatisfied with current ways of measuring humanity’s achievements. Future work in this field will be read avidly in those circles.
You can read the actual report of Dr. Neve’s study here. As always, share your thoughts or illuminations below.