A person's disposition toward happiness or misery is genetic, scientists have proved during the past two decades.

As much as one-third of the difference in people's happiness levels is passed on through DNA, according to a report jointly compiled by scientists from University College, London, Harvard Medical School, the University of California, San Diego, and the University of Zurich. They examined more than 1,000 pairs of adolescent US twins in a study published in the Journal of Neuroscience, Psychology and Economics in 2011.

The chemical contributors to happiness are mainly serotonin and dopamine, which are neurotransmitters secreted by cells. Their levels are determined by a person's DNA. The higher the levels of these chemicals, the happier a person is.

Some women have a "happiness gene", which allows a higher concentration of serotonin and dopamine in their brains, according to a separate study co-conducted by the University of South Florida, Columbia University and the US National Institutes of Health.

Gender split

Women with the gene Monoamine oxidase A reported significantly higher levels of happiness than those without. Moreover, their level of happiness was higher than men both with and without the gene.

"This is the first happiness gene for women," said study leader Henian Chen of the University of South Florida. Chen's team examined the DNA of 193 women and 152 men in the study, which was published in the journal Progress in Neuro-Psychopharmacology & Biological Psychiatry in August 2012.

Some men also have the gene, but it doesn't have the same effect. In addition to happiness, the gene has also been associated with negative traits, such as alcoholism, aggressiveness and antisocial behavior.

Indeed, before the discovery of its specific application for women, Monoamine oxidase A was known as "The warrior gene", and Chen's team speculated that testosterone may have mitigated its positive effects.

Controversial report

A more controversial study examined the gene 5-HTTLPR, which transports serotonin through the cells. The team was led by Jan-Emmanuel de Neve of the London School of Economics. Its report was published in the Journal of Human Genetics in 2011.

There are long and short versions of 5-HTTLPR, one from each parent. The long version produces more serotonin-transporting molecules than the short. Both versions of the gene are carried by all human beings. Some people have two long genes, some have two short genes, and others have one long and one short.

Those adolescents with one long gene were 8 percent more likely to describe themselves as very satisfied than those with two short genes, while those with two long genes were 17 percent more likely to make that claim.

At this point, the study becomes contentious: All 2,500 adolescents surveyed were US citizens, but on average, the Asian-Americans in the sample had 0.69 long genes, while the number was 1.12 for the white subjects and 1.47 for black subjects.

(China Daily USA 09/06/2013 page7)