Women laugh amid the daffodils in Green Park in central London March 15, 2014.
Women laugh amid the daffodils in Green Park in central London March 15, 2014. Reuters/Olivia Harris

Genes could be behind the reason why some people tend to smile or laugh at simple things, according to a new study. Researchers said that people who have short alleles of a gene called 5-HTTLPR laughed or smiled more compared to those who have long alleles.

In the study performed in the laboratories of Robert W Levenson and Dacher Keltner at University of California, Berkeley, scientists analysed short and long alleles of the gene that is involved in regulating the levels of serotonin, the neurotransmitter involved in depression and anxiety. They then recorded on videotape the participants doing some facial expressions, making sure that there were identifiable signs of genuine amusement.

The study, published in the journal Emotion, involved 336 participants in total who took part in three different experiments assessing emotional reactivity. Scientists then collected samples of their saliva to prove if they have short or long version of the gene. Overall, the study showed that those who had short alleles produced more genuine smiles and laughter compared to participants who had long alleles, UC Berkeley News Centre reported.

Researchers also conducted another study before and it found that those with short alleles were more sympathetic of their partner’s emotions, both negative and positive. The previous study suggested that marital satisfaction has something to do with DNA. Lead author of the study Claudia Hasse said in her statement that the new study “provides a more complete picture of the emotional life” of those who have the short variant of the gene.

Hasse, an assistant professor at Northwestern’s School of Education and Social Policy, also said in a report from EurekAlert that having the short variant does not mean it is bad or it can be risky. "Instead, the short allele amplifies emotional reactions to both good and bad environments," she said.

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