In a social environment and due to niche-specific and frequency-dependent selection, divergent physiologic and behavioral stress responses will be maintained in a population because the benefits and risks of opposing behavioral strategies will balance one another in different contexts. Two basic behavioral phenotypes have been observed and are thought to be maintained by balancing selection in a wide variety of animal species, including humans. While one is characterized as being aggressive and bold, adopting a more proactive coping style, and fight or flight responses to stress, the other is more harm avoidant and exhibits reactive, anxiety-like behaviors following stress. A conceptual framework has been put forth that suggests differences in these behavioral strategies to have implications not only in terms of selection, but in terms of vulnerability to psychopathology 10. The CRH system is proposed to critically contribute to such differences. There is evidence that variation at the CRH locus predicts levels of behavioral inhibition in children 59, and genetic variation at the CRHR1 locus is suggested to be a risk factor for alcohol problems. Functional CRH haplotypes have been
