The Danish are consistently ranked as the world's happiest people, and a new study shows that the key may be found in their DNA.

Researchers at the University of Warwick's Centre for Competitive Advantage in the Global Economy wanted to find out why countries such as Denmark and the Netherlands regularly outrank similar high-GDP European countries in happiness. They found three kinds of evidence suggesting high levels of life satisfaction may not be entirely due to standard of living, but rather to genetics.

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The first part of the study measured the "genetic distance between countries' populations," a concept developed in previous studies. The researchers analyzed international survey data from 131 countries, adjusting for influences like Gross Domestic Product, geography culture, religion and strength of welfare state.

"The results were surprising," economist Eugenio Proto, one of the study's authors said. "We found that the greater a nation’s genetic distance from Denmark, the lower the reported well-being of that nation."

In other words, the more closely-related a country's population is to Denmark, the happier that country is. The study's second analysis found happiness levels correlate with a gene that influences serotonin, a chemical in the brain that is thought to stabilize moods. The short variant of the gene is tied to neuroticism and lower life satisfaction, and the long variant is tied to higher life satisfaction.

"Intriguingly, among the 30 nations included in the study, it is Denmark and the Netherlands that appear to have the lowest percentage of people with this short version," Proto said.

The study also looked at data on U.S. immigrants to see if the genetic link to happiness persisted over generations. Consistent with the genetic explanation, the study found levels of happiness for people in the U.S. correlated with the levels of happiness in their country of origin.

“We used data on the reported well-being of Americans and then looked at which part of the world their ancestors had come from," researcher Andrew Oswald said. "The evidence revealed that there is an unexplained positive correlation between the happiness today of some nations and the observed happiness of Americans whose ancestors came from these nations, even after controlling for personal income and religion.”

Researchers noted these results "should be treated cautiously," and Oswald said more work must be done to understand the causes of international well-being levels.

"More research in this area is now needed and economists and social scientists may need to pay greater heed to the role of genetic variation across national populations," he said.