Nicholas Wade of the New York Times writes about the genetic components of social behavior. Reporting on a new analysis by Jonathan Pritchard of the University of Chicago, he writes:
Evolutionary changes in the genome could help explain cultural traits that last over many generations as societies adapted to different local pressures.
Pritchard found more than 700 parts of the human genome that have changed in recent times -- by evolutionary standards, at least. The average age of the changes was 6,600 years.
Some changes could be the result of diet, such as genes that allow the digestion of lactose, which became prevalent in inhabitants of what is now Sweden and Holland, where the practice of drinking cow's milk began.
But this rapid genetic change also can explain societal traits, Wade says, specifically the develoment of high-trust or low-trust societies.
Oxytocin levels are known to be under genetic control in other mammals.
It is easy to imagine that in societies where trust pays off, generation after generation, the more trusting individuals would have more progeny and the oxytocin-promoting genes would become more common in the population.
So, when we travel to a country or region where "the people are so warm and friendly," we may be experiencing a real genetic and biochemical difference.
UPDATE: Brad DeLong's Semi-Daily Journal has a discussion among people who know a lot about statistics, some of whom dispute the science in Wade's story.