I believe an evolutionary psychological theory provides a much simpler and more parsimonious explanation for the desistance effect of marriage for both crime and science, in the form of a single psychological mechanism that predisposes young men to compete and excel early in their adulthood but subsequently turns off after the birth of their children (which quickly followed and regular in the absence of reliable means of birth control in the ancestral environment). After their marriage and children, male scientists do not feel like spending hours and hours in their labs, just like married criminals do not feel like taking great risks and committing crimes. But neither scientists nor criminals know why.

From the evolutionary psychological perspective, reproductive success is the end, and everything men do (be it crime or scientific research) is but a means to this ultimate end. From this perspective, the question of why marriage depresses crime and scientific misses the whole point. Does it make sense for men to continue empmloying the means even after they have achieved the ends they were trying to attain with the means? This is why married men are less likely to engage in a whole range of behavior, like driving fast, which are designed indirectly and unconsciously to attaract women. Indeed, automobile insurance statistics clearly show that married men have fewer car accidents.

Fluctuating levels of may provide the biochemical microfoundation for the desistance effect of marriage and on men, be they criminals or scientists. One longitudinal study shows that men's levels of testosterone go down when they get married, and go up when they get . Another study demonstrates that expectant fathers' testosterone levels fall precipitiously immediately after the birth of their child. If high levels of testosterone predispose men to be more competitive and aggressive, then the sudden drop in testosterone after their marriage and the birth of their child may provide the biochemical reason why men's psychological mechanisms to commit crime and produce scientific work “turn off” when they get married and become fathers.

I will conclude this series with the next post on a few observations on how the media treated this research.