>>14155938There's no doubt that especially brutal wars that leave only a few standing on either side have had severely dysgenic effects on the surviving population as a brutal war would kill off a large portion of the gene pool and most likely leave the worst specimens to reproduce. But at the same time you have to consider the eugenic effects that war and fighting have had at the group and individual level, especially in mankind's early history.
At the individual selection level the smarter and stronger male phenotypes would ultimately reproduce more. War, especially ancient warfare, disproportionally selects for strength and smarts. Add to the fact that the victor would get the loser's women and suddenly the victor has significantly increased the amount of their genes in the genepool. In essence, war doesn't lower the reproductive fitness of the victor, but increases it.
And of course you just can't consider war from an individual selection theory, but from a group selection theory as well. The group that can fight cohesively and is made up of individuals willing to sacrifice themselves for the cause of the group will be more successful than an individual or an incohesive group. A group incapable of fighting for their own resources would be quickly selected against.
It could be argued that modern warfare no longer selects on the individual level and mostly selects at the group level. Thus modern warfare is completely dysgenic at the individual level.
Finally, to answer your main question, war isn't selecting for the most "peaceful" participants, it selects for the smartest, strongest, and in some cases, luckiest groups or individuals. Those who win a war are bound to be capable of aggressiveness and violence. The selection for peacefulness would most likely happen at an intrasocietal level in the form of selective mating or social ostracization, really any thing that would lower the reproductive fitness of a violent individual.
