Scientists claim to have discovered the "happiness gene" which they say has a strong influence on how satisfied people are with their lives.
A team from the London School of Economic and Political Science found that people with two sets of the gene -- one from each parent -- are almost twice as likely to say they are satisfied with life, compared to those who lack a copy.
The gene, called 5-HTT, is responsible for how well nerve cells manage to distribute serotonin, a chemical produced by the pineal gland in the brain which helps control mood, the Daily Telegraph reported.
People with low levels of serotonin -- nicknamed the "happiness drug" -- are known to be more prone to depression.
Now, the researchers have found evidence that people with the "functional" variant of the 5-HTT gene tend to lead happier lives.
Lead researcher Jan-Emmanuel De Neve said: "It has long been suspected that this gene plays a role in mental health but this is the first study to show that it is instrumental in shaping our individual happiness levels.
"The results of our study suggest a strong link between happiness and this functional variation in the 5-HTT gene."
For their research, De Neve and colleagues asked more than 2,500 people in the US about how satisfied they were with life, and also analysed their DNA for presence of the gene.
The 5-HTT gene provides the "operating code" for transporting serotonin in neuron cell walls. The "long" version of the gene leads to more serotonin transporters in these walls, while the "short" version less of them. As we inherit a set of genes from both parents, the possible combinations of this are "long-long", "long-short" or "short-short".
The researchers found that 69%of people who had two copies of the gene said they were either satisfied (34) or very satisfied (35) with their life as a whole. But among those who had no copy of the gene, the proportion who gave either of these answers was only 38 per cent (19% "very satisfied" and 19% "satisfied").
De Neve said: "Of course, our well-being isn't determined by this one gene -- other genes and especially experience throughout the course of life will continue to explain the majority of variation in individual happiness.
"But this finding helps to explain why we each have a unique baseline level of happiness and why some people tend to be naturally happier than others, and that’s in no small part due to our individual genetic make-up."
The study is published in the Journal of Human Genetics.