This OP was created in response to a PM received which read as such, "(https://www.aic.gov.au/publications/tandi/tandi263) Shows that there may be certain traits of passing down criminal susceptibility, but it is not certain or even likely for this to happen, so a mass killing of violent individuals would not accomplish this via evolution".
This quote was in direct response to the studies I'm about to provide, and since the person in the PM said that I hadn't refuted anything he said, I decided to bring the discussion to the forums. In this OP, I will show that 'criminal susceptibility' in the European genepool was heavily reduced due to the 'war on murder'.
War on murder
In short, the Catholic church started to change its tune on criminality around the 12th Century, and thus things like the death penalty began to become existent in Europe. Harpending and Frost (2015) showed that somewhere between 1-2% of each generation's male population was executed for violent crime. https://journals.sagepub.com/doi/pdf/10.1177/147470491501300114 .
Over 30 generations (assuming each is approximately 25 years), you are eliminating each generation's most violent criminals, and hence their genes which made them violent. Moreover, these violent genes set left the gene pool, and the gene pool reshuffled for the next generation *without* that most violent gene set being a part of it. Over time, this meant that the extreme end violent genetic clusters became less and less.
Thus, in effect, removing the most violent 0.5-1% of the population's most violent genes, results in removing about 45% of the violent genes altogether (since the effect is compounded, not a singular generational removal of 22.5%). Thus, the PM quote saying that this is a "mass killing" is misaligned with this phenomenon, because it was not a singular "mass killing", but rather killings that compounded over time to produce a far different effect.
Note that the AIC government source the PM cites was produced in 2003, well before the existence of this 2015 data. Thus, at the time of publication, it is entirely possible that the AIC was correct in its conclusions, at the time of publication.
Severe reduction in homicide rates throughout Europe
The result was that from approximately 1300-1900, homicide rates plummeted in Europe https://www.vrc.crim.cam.ac.uk/vrcresearch/paperdownload/manuel-eisner-historical-trends-in-violence.pdf . Eisner (2003) completed work estimating homicide rates across various European countries, compiled on this graph https://i.imgur.com/ofIRsYm.png
As you view these graphs, an important point is that they are logarithmic, so a decline from a y-axis interval to another (e.g. 100 to 10) is 10 times a reduction. Understanding this should make the gravity of the data for more potent.