Genes Determine Whether You Are Quick To Laugh Or Smile

by Monica Joshi

Ever notice how some people just can't control whether they smile or laugh at a silly joke? For some, smiling is their default, while for others it's laughing. New research from Northwestern University and the University of Geneva shows that the key to this response may lie in a person's DNA.

A new study, combining three different experiments from different Berkeley labs, examines emotional reactivity and links a particular gene to positive emotional expressions such as smiling and laughing.

The researchers looked at short and long alleles of the gene 5-HTTLPR, which is involved in the regulation of serotonin, a neurotransmitter implicated in depression and anxiety. An allele is a variant of a gene and although each gene has two alleles, humans inherit one allele from mom and one from dad. Early research suggested that short alleles predicted unwanted negative outcomes such as depression, anxiety and substance abuse. Also, those with short alleles were found to have higher negative emotions than those with long alleles.

Claudia M. Haase of Northwestern University and Ursula Beermann of the University of Geneva co-authored the study now published in the American Psychological Association journal Emotion. The study, a three-part experiment, was actually conducted in the laboratories of Dacher Keltner and Robert W. Levenson at the University of California, Berkeley.

For the first experiment, young adults were shown cartoons from “The Far Side” by Gary Larson, and The New Yorker. Then, for the second experiment, young, middle-aged and older adults watched a somewhat amusing clip from the film “Strangers in Paradise.” The 336 participants who were included in the final experiment were asked to discuss an area of disagreement in their marriage.

The scientists videotaped the volunteers during the experiments. These tapes were then coded as either 'smiling' or 'laughing' using the “Facial Action Coding System,” which describes small movements in the face. The researchers noted that people with short alleles of the gene 5-HTTLPR smiled or laughed more while watching cartoons or somewhat amusing film clips, than people with long alleles.

As people are sometimes prone to smiling or laughing even if they don't find something funny, e.g. to be polite or hide negative feelings, the study was geared to focus only on ‘real’ positive emotional expressions.

Hasse made it a point to note that:

“So when you measure smiling and laughing, you want to be able to distinguish real laughs and smiles from the ones that aren’t. The important clues lie in the muscle around the eyes that produce the so-called ‘crow’s feet. Those can only be seen in real smiles and laughs."

Finally, the researchers collected saliva samples from the participants to analyze the 5-HTTLPR gene. The data from the three experiments suggested that people with the short allele of 5-HTTLPR showed greater positive emotional expressions. People with the short allele displayed greater genuine smiling and laughing than people with the long allele.

The latest study adds to previous research suggesting that people with short alleles may also be more sensitive to the emotional highs and lows of life. While previous research had linked the gene to negative emotions, this study has the strongest evidence to date that the same gene is also linked to positive emotions.

With regards to whether or not people with short alleles may be at a disadvantage, Haase said:

“People with short alleles may flourish in a positive environment and suffer in a negative one, while people with long alleles are less sensitive to environmental conditions.”

This new research could be useful in understanding the way people react to and deal with more stressful environments. More research should be done on whether this gene variant can actually affect the way that people handle situations in a work environment.