Anthropologist Peter Frost and anthropologist and population geneticist Henry Harpending argue that killing murderers pacified the population eugenically.
At the beginning of … the English homicide rate was about 20 to 40 per year per 100,000 people. At the end [1750, AT], it was about 2 to 4 per 100,000, i.e., a 10-fold reduction (Eisner, 2001).
…Can this leftward shift be explained by the high execution rate between 1500 and 1750? During that period, 0.5 to 1% of all men were removed from each generation through court-ordered executions and a comparable proportion through extrajudicial executions, i.e., deaths of offenders at the scene of the crime or in prison while awaiting trial. The total execution rate was thus somewhere between 1 and 2%. These men were permanently removed from the population, as was the heritable component of their propensity for homicide. If we assume a standard normal distribution in the male population, the most violent 1 to 2% should form a right-hand “tail” that begins 2.33–2.05 SD to the right of the mean propensity for homicide. If we eliminate this right-hand tail and leave only the other 98-99% to survive and reproduce, we have a selection differential of 0.027 to 0.049 SD per generation.
…The reader can see that this selection differential, which we derived from the execution rate, is at most a little over half the selection differential of 0.08 SD per generation that we derived from the historical decline in the homicide rate.
Thus, the authors argue that it is possible that a substantial decline in criminality can be explained by the eugenics of execution. The authors, assume, however, that executed criminals have no offspring which is unlikely, especially if criminals have higher fertility rates.
Hat tip to PseudoErasmus on twitter.