Wars end up with those best at surviving surviving. The ones best at getting allies to protect them, the ones who keep their children alive even at the cost of thousands of others' lives, the ones who groom an ally to throw themselves on the grenade, the ones who climb the power ladder and then use that power to keep themselves safe from the conflict…

War is a terrible selection pressure, if you value the light and good in this world. (Probably) less bad than the ones genocidal dictators apply, given how indiscriminate (and therefore bad at selection) it is, but it's certainly not in the “good” category.

> wars do end up with mostly the fittest (not just in terms of physical ability, but also intelligence, cunning, etc.) surviving.

1.) There is massive random factor.

2.) The fittest are often selected for unit that have large mortality. That was the case of SS in Germany - supposed to be the fittest selection. And as result going to hardest fights dying the most.

In Russia, it was year of birth that made difference. The guys who were 18 by the start of the war died almost all. You was better off if you was 17 or 22.

3.) The fact is, the fit male goes to combat and is more likely to die. The weaker one who wont be selected for that, survives.

War kills off the healthy, the young, the brave, the stress-resistant and so on. All of these are qualities that can make society better in a context of peace, but are a liability in the context of war from the perspective of the individual. The deformed, the less healthy and those adept at finding loopholes get to stay at home. A war on a massive scale thus has a negative effect on long term fitness.