Here the researchers pointed out the more "aggressive" behavior of the Datoga people compared to the quieter Hadza people. When they did the genetic studies, they concluded that culture (instead of genetic habitancy) caused the variation in genetic results. It seems that a European industrial population showed no differences in aggressiveness in the serotonin genes studied. We would suggest that the serotonin genes didn't affect aggressiveness.
The researchers found that the serotonin genes differed between more aggressive individuals of the more aggressive population. This would mean to me that the serotonin genes were affecting other aspects of personality instead of Aggression since the entire population was homogeneous as to behavior.
At any rate until NPA traits are understood and NPA habitancy theory, there will be conclusions that culture and environment are a cause of phenomena when actually genetics are the cause.