This study of crickets asks the question of how a genetic trait of behavior, here aggression, stabilizes its prevalence in a population. The conclusion is something like, "the ripple effect of the trait in the population." To NPA theory, aggression is always accompanied by submissiveness trait and pseudo-submissiveness. And one can't exist without the other similarly to how good can't exist without evil and pain can't exist without pleasure.
NPA theory holds that Aggression trait appeared and was seleccted strongly as it has spread over the entire earth from its first appearance just "east of Eden" (just east and north of Africa
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