Hearing the same joke, some people laugh until they cry, but some people do not have any reaction. Watching a tearjerker, some people cry throughout, but some people can still laugh. What cause these difference? It is easy for us to combine these reactions with cultural factors, personal experience and personality. Actually, they are not all the answers for this question.
Recently, a paper published in “Emotion” shows that genes may affect emotional expression. The present research examined the effect of the 5-HTTLPR polymorphism in the serotonin transporter gene on objectively coded positive emotional expressions. By the way, Researchers commonly report it with two variations in
humans: the short allele (“s”) and the long allele (“l”). Three studies with independent samples of participants were conducted. To be specific, study 1 examined young adults watching still cartoons; study 2 examined young, middle-aged, and older adults watching a thematically ambiguous yet subtly amusing film clip; and study 3 examined middle-aged and older spouses discussing an area of marital conflict (that typically produces both positive and negative emotion).
I want to introduce the way researchers code participants’ emotional expressions. It is named Facial Action Coding System (FACS). FACS is a research tool useful for measuring any facial expression a human being can make. It is an anatomically based system for comprehensively describing all observable facial movement. So it helps researchers to test and analyze objectively without experimenter effect.
After analysis of three studies, results showed that the short allele of 5-HTTLPR predicted heightened positive emotional expressions. To sum up, people with “s” allele (genotype is ss or sl) are more sensitive and more easily to affect by environment, experience and stimulus. In order words, the more “s” alleles people have, the more times they laugh.
If you think this research is not very convincing, I find another paper published in 2012 having the similar conclusion. The researchers identified 77 pertinent effect sizes on 9361 subjects from 30 reports, providing data for two meta analyses on the moderating role of 5HTTLPR when it comes to the impact of the environment on development. According to this research, “we found 41 effect sizes (N = 5863) for the association between negative environments and developmental outcomes with or without significant moderation by 5HTTLPR genotype and 36 effect sizes (N = 3498) for the potentially 5HTTLPR-moderated association between positive environments and developmental outcomes”. Then they got a result that people with “s” allele, called them ss/sl carriers were significantly more vulnerable to negative environments than ll carriers, which support the diathesis-stress model. These children are easy to have emotional disorder in adolescence if they would face unfortunate experience. Controversially, they also benefit more if they could grow up in healthy and warm environment. So this result just fits in the previous experiment’s conclusion.
Although we get the conclusion, we still have a lot of space to explore in the neurobiological mechanism to find the specific results. But at least now we know that laugh or not can be caused by our genes, which I never imagine before. So next time when you see someone appears distant to you, it may not mean that he or she doesn’t like you, but means that he or she doesn’t have many “s” alleles. ?