[tossaccount123]

Common sense would tell you there's some truth to it. For centuries we killed murderers and rapists and thus removed them from the gene pool. Data shows testosterone levels, which are correlated with violence, have dropped massively over the last few decades, whether that is genetic or environmental and to what extent for each is up for debate

WWI and WII basically selected to kill off Europe's bravest and most nationalistic men, those who immediately signed up to fight and were thrown in the meat grinder.

I'm partly convinced that's why America is so different from Europe, we managed to avoid most of the carnage of those wars

[toasterlovin]

Don't forget that immigrants to America were probably skewed toward certain personality types. And, of course, all personality traits are heritable to some degree.

[iguy]

There is a neat paper I can't find which runs the numbers. So from memory:

For about 1000 years, we know that west-european states executed about 1% of each generation. Assume it's the most violent 1%, and that violence is 50% heritable. Plugging these into standard formulas for animal breeding, and I believe the answer is that this explains about half the decline in the murder rate over this period.

Obviously there are some giant caveats here. But it's super-interesting that a back-of-the-envelope calculation gets you the right order of magnitude.

I'm dubious though of wars doing much. The big 20th C meat-grinder was largely conscripts. And anyway I'm not sure how correlated with blood-thirst most recruiting was. Whereas getting yourself hanged for murder in peacetime was pretty tightly correlated.