Researchers have discovered that the majority of people living in countries considered to be collectivist have a certain mutation within a gene that regulates the transport of serotonin, a neurochemical known to have a substantial affect on mood. For example, in China and other east Asian nations, up to 80% of the population carry this so-called "short" allele, or variant, of a stretch of DNA known as 5-HTTLPR. Previous research had revealed that the S allele is greatly connected to a variety of negative emotions, such as anxiety and depression. What is even more serious is its association with the impulse to protect oneself and avoid harm. On the flip side, in countries of European origin that tend toward self-expression and individuality over group goals, the long or "L" allele dominates, with only 40% of people carrying the "S" variant. Scientists believe that cultures exposed to high levels of deadly pathogens, such as ancient cultures in Asia, Africa and Latin America might have leaned more toward collectivist norms in order to stave off disease. Such a social transformation would have then favored the gradual dominance of the risk-avoidance S allele.
coevolution of individualism–collectivism and the serotonin transporter gene
'Culture of we' buffers genetic tendency to depression
Germs, collectivism and serotonin