Depression is a beast of two parts: genetic predisposition and environmental influence. Someone with high genetic predisposition will require less environmental influence for symptoms to manifest. Likewise, someone more fortunate in the genetic lottery can handle more external influence.
A new Northwestern University study from the growing field of cultural neuroscience suggests that it’s a bit more complicated than that. The missing variable from the original equation is culture—not merely as an environmental influence, but as an internalized influence that alters gene expression from the inside out.
Previous research has shown that the serotonin transporter gene (STG) is a linchpin factor for people with depression. The gene has two variants: a short allele and a long allele (allele being an alternative form of a gene located at a specific position on a specific chromosome). In Western populations, the short allele is linked to major depressive episodes when people who carry it experience multiple life stressors.
Nations in East Asia have a disproportionate number of short allele carriers, so a biological assessment would lead you to believe that those nations also have a higher number of people with depression.
Except, they don’t. In fact, the Northwestern researchers found that even in nations where as much as 80% of the population is at greater risk of depression, the actual depression percentage is far lower than comparably populated Western nations.
What the researchers believe explains the discrepancy is culture. Eastern nations are typically collectivistic; Western are more individualistic. Quoting from Joan Chiao, lead author of the study:
People from highly individualistic cultures like the United States and Western Europe are more likely to value uniqueness over harmony, expression over agreement, and to define themselves as unique or different from the group. [People in collectivistic cultures] more likely to endorse behaviors that increase group cohesion and interdependence. Science Daily, 10/30/2009
The biggest cultural gene-buffering factor could be social support. Collectivist cultures may give people who are genetically susceptible to depression an expectation of social support that guards against environmental stressors. That expectation is generally lacking in Western cultures, where “sink or swim” is a more common mentality.
The major takeaway from this study is that culture isn’t just an external factor. The way we think about ourselves isn’t merely influenced by culture—in a very real sense it’s defined by culture. And that definition, which encapsulates our thoughts and actions, underlies how we react to other stress-laden things in our environment (relationships, jobs, finances, driving, food, media, etc). This study shows that the overriding characteristic of a culture—its “me” or “we”-ness—is stronger than genetic predisposition.
Here’s a story about another study that examined whether genes or culture are more influential in manifesting altruistic behavior.