Another example:
Consider Maslow's hierarchy and the Myers Briggs Personalty Type Indicator. There are 4 major personality types, and Guardians make up almost half of the total. Artisans and Idealists? Not so much. That is exactly what would be predicted when you consider the struggles to pass along DNA that have existed for 100,000 years. Those with the personality type to protect themselves and their offspring, and excel at safety/security/food (the bottom rungs of Maslow's hierarchy) would be the 'fittest' in the early parts of the homo-sapien journey (and get the girls).
Civilization likely had to be more firmly stablished before idealists and artisans, who sit at the top of Maslow's pyramid in the self-actualization categories, could flourish - and live long enough to pass along their DNA (and get the girls).