According to a research, the more people in a country who have a particularly gene, the happier the nation will be. The DNA in question, the FAAII gene, makes a protein(蛋白质)that affects feelings of pleasure and pain. People with a particular kind of it tend to be cheerier souls.

   However, wealth and health were found to have little effect on happiness. The researchers said it could help explain why some of the world's poorest nations are also the happiest. The team from Bulgaria and Hong Kong looked at whether there was a link between levels of the FAAH gene in a population and number of people who said they were very happy in global study of life satisfaction. Sweden—one of the happiest countries in Europe and in the world—also had lots of happy DNA. Some 26.3 percent of Swedes have the happiness gene, compared to 23 percent of Britons, 21 percent of the French and 20 percent of Germans. The happiness gene is even rarer in southern Europe, where it is found in 18 percent of Greeks and just 12 percent of Italians. In contrast, the people of Jordan, Hong Kong were among the least likely to rate themselves as very happy and also had the lowest levels of the gene.

   But the gene and optimistic outlook didn't always go hand in hand. For instance, Russians and Estonians score very low on happiness, despite having the "right" DNA, the Journal of Happiness Studies reports.

   Climatic differences were also found to be significantly associated with national differences in happiness. Study co-author Michael Minkov, said:"We cannot fail to notice the high occurrence(发生)of the gene in hot and tropical(热带的)environments in the Americas and Africa and the lower occurrence of it around the Mediterranean Sea than in Northern Europe.