A recently published study from UCSB psychology researchers Aaron Lukaszewski and James Roney shows that variations in extraversion may be linked to physical strength and physical attractiveness.

Lukaszewski, a postdoctoral scholar at UC Berkeley, is the first author of the study, which was published in the journal Personality and Social Psychology Bulletin of the Society of Personality and Social Psychology. The researchers focused on a somewhat-overlooked mechanism in personality psychology called “facultative calibration” in order to explain variations in extraversion that were previously thought to be highly heritable or dominantly controlled by genes. Facultative calibration is the process by which certain genetic traits, such as strength, have an influence on personality traits, such as extraversion.

“The paradigm of personality psychology is that much of personality is heritable, but the problem is that you can’t always find the gene,” Lukaszewski said. “And if you do find the gene, then it only explains a small part of the variance.”

Variations in extraversion cannot simply be explained by their own heritability but may rather be explained by their association with other heritable characteristics.

“Physical characteristics are based on genetic differences, and if your personality is calibrated with those, then it explains why your personality traits show up as heritable,” Lukaszewski said.

The study shows that individuals with higher measures of physical strength and physical attractiveness are more likely to be extraverted.

“If you’re getting feedback that says you’re attractive, it makes sense to play an extraverted strategy,” Roney said in a press release. “If you’re getting feedback that you’re less attractive, then it makes sense to be introverted. The same is true for strength, especially for men.”

Lukaszewski and Roney also examined a gene that appears to be a predictor for extraversion. This gene, which codes for androgen receptors, is responsible for taking in hormones, such as testosterone. People have different numbers of Cytosine-Adenine-Guanine (CAG) codon repeats at this gene locus, which affects the activity level of their androgen receptor.

“The shorter the number of these repeats, the more active the receptor is,” Roney said in a press release. “This means that if two men had exactly the same testosterone, the one who had the shorter number of repeats would convert that same amount of testosterone into larger effects — such as greater muscle mass — because the receptors are doing more with the same amount of hormone.”

The researchers concluded that 20 percent to 40 percent of extraversion variance could be explained by the variables of physical strength and physical attractiveness.

“The primary take-home — that strength and attractiveness can explain 20 to 40 percent of the variance — is really pretty surprising because they do not share a common genetic basis,” Lukaszewski said.

This study presents a different perspective for the study of other personality traits.

“Facultative calibration could be a foundational concept for personality psychology,” Lukaszewski and Roney said in their study. “If these arguments are correct, they carry important implications for the field of behavior genetics.”

The study’s findings may open doors for further inquiry about the source of other personality traits whose origins are still relatively unclear.