Don’t smile enough? Blame your parents

Do you have resting bitch face? I do, big time. Yet despite my stone-cold neutral expression, I’m pretty quick to crack a smile and giggle like a schoolgirl when the right material is thrown my way—including Cathy comics (so true!), my roommate’s cat, or a well-executed Spongebob Squarepants Vine.

Turns out I may have my parents to thank for these bursts of joy: A new study has linked emotional reactivity to our genes.

The research, published this month in the journal Emotion, was a joint effort between Northwestern University and University of California-Berkeley. The researchers found that those with a genetic predisposition for experiencing negative emotions were also more likely to experience positive emotions.

For example, while a conflict in your relationship with your partner may take a heavier toll on you emotionally if you have this predisposition, the pendulum swings the other way, too—the positive parts of your relationship make you feel even happier and are all the more rewarding. Hey, some folks are just sensitive.

To gauge emotional reactivity, the researchers enlisted a few groups of participants to look at, well, some funny stuff. In the first experiment, they had young adults look at Far Side and New Yorker comics. In another, they had people of all ages watch a “subtly amusing” bit from a movie. And in the third study they had middle-aged and elderly married couples talk about a disagreement they’d had in their relationship.

The researchers filmed the participants and used a software to code their facial expressions—particularly their smiles and laughter. Because it’s easy to fake a smile, they took special pains to suss out “genuine” smiles, or when the participants smiled with their eyes.

Then the researchers took saliva samples from the participants to study their “alleles” of the gene 5-HTTLPR, which transports the neurotransmitter serotonin and plays a role in emotions, mood disorders, and other psychiatric conditions. We have two alleles for every trait (one from our mother and one from our father)—the dominant one is expressed, and the recessive one is masked.

In the case of 5-HTTLPR, the researchers looked at two variants of the gene: short alleles and long alleles. Previous research found that short alleles were linked to “negative outcomes” and disorders such as depression, anxiety, and substance abuse. But the researchers found that those with dominant short alleles also smiled and laughed more.

“Our study provides a more complete picture of the emotional life of people with the short allele,” Claudia Haase, assistant professor of human development and social policy at Northwestern and co-author of the study, said in a statement. “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.”