Did the imposition of the death penalty result in selection against violent behavior?

I meant to post this study a while ago, but didn't have the time...

Western Europe, state formation and genetic pacification...
http://www.epjournal.net/articles/w...mation-and-genetic-pacification/getpdf.php?fi
le=EP1302300243.pdf

"Through its monopoly on violence, the State tends to pacify social relations. Such pacification proceeded slowly in Western Europe between the 5th and 11th centuries, being hindered by the rudimentary nature of law enforcement, the belief in a man’s right to settle personal disputes as he saw fit, and the Church’s opposition to the death penalty. These hindrances began to dissolve in the 11th century with a consensus by Church and State that the wicked should be punished so that the good may live in peace. Courts imposed the death penalty more and more often and, by the late Middle Ages, were condemning to death between 0.5 and 1.0% of all men of each generation, with perhaps just as many offenders dying at the scene of the crime or in prison while awaiting trial. Meanwhile, the homicide rate plummeted from the 14th century to the 20th. The pool of violent men dried up until most murders occurred under conditions of jealousy, intoxication, or extreme stress. The decline in personal violence is usually attributed to harsher punishment and the longer-term effects of cultural conditioning. It may also be, however, that this new cultural environment selected against propensities for violence. "

What do you think?

Not violence per se but uncontrolled violence. Cops use violence after all .

Intriguing idea, though I'm not convinced it did the "cleaning" job in society the way they describe, or only in this time period. Even before 11 century, before proper states existed, there were smaller tribal/landlord systems with there own laws and death penalties, not mentioning justice on village level, the village justice, "adjusting" many anti-social behaviors in violent way.
There could have been a balancing act in relation of bad people to good ones. At least there was one big war in every country every generation. War took many law obeying, good people who stood up to protect their country and people. Many good characters also died during many uprisings against occupants through history of Europe.