The key to happiness may lie in your genes.

Psychologists at the University of Edinburgh and the Queensland Institute for Medical Research in Australia have found that happiness is partly determined by personality traits that are largely hereditary, along with your situation in life.

The researchers used a personality test called the Five-Factor Model on more than 990 twin pairs. Matching that with happiness data taken from the pairs, they found that people who do not excessively worry, and who are sociable and conscientious tend to be happier.

The research, detailed in the March issue of the journal Psychological Science, identified evidence for common genes that result in the personality traits that predispose people to happiness, the researchers said.

"Although happiness is subject to a wide range of external influences we have found that there is a heritable component of happiness which can be entirely explained by genetic architecture of personality," said study team leader Alexander Weiss of the University of Edinburgh.

While these genes won't guarantee happiness, the personality mix they result in could act as a trigger when bad things happen, allowing people to have an "affective reserve" of happiness that can be called upon in stressful times.

And while the genetic influence is strong, about 50 percent of the differences in people's happiness in life can still be chalked up to a variety of external factors, such as relationships, health and careers. Research done by Ed Diener of the University of Illinois finds that the happiest people have strong friendships, for example