I can't stop thinking about Papua New Guinea

"The Cutting-Off Way: Indigenous Warfare in Eastern North America, 1500-1800" by Wayne Lee is a good read that describes a similar kind of warfare. It doesn't necessarily prove (nor does it set out to prove) that all non-industrial warfare followed this model but it does provide decent evidence for population-limited societies generally preferring deadly ambush to pitched battle.

When running away is a big part of the tactic, it's not a "kill everyone" tactic. You don't have the advantage for long. And even if you did succeed, the next tribe over could just as easily do the same to you (and they probably would, seeing what you're like), so there's a strong reason to develop norms, rules of engagement limiting this sort of thing.

The versions I've heard always included bringing back any cattle and/or women you could. That gives the raids a more demonstrable benefit.

I think this makes the common mistake that all "primitive" cultures have the exact same behavior -- I suppose you're not speaking from PNG right? (although likewise I have no such specific knowledge) As the article cites, in this specific place (and in many other similar cultures), I don't think there's motive to wage large scale wars or take large amounts of territory, that would justify something like raiding and wiping out other groups. I suppose that could happen in the huge number of other cultures, ones that had more centralized leadership or competing more unified cultures. The conflicts in the case of PNG might have been localized dispute over borders and such.

In nonhuman animals, even in fierce disputes over territory and mating, killing is rare, because it's quite costly: you eliminate completely a healthy individual, and usually would run the risk of serious injury yourself, making both dying likely. Usually they e.g. resolve mating with displays of beauty/fitness, and territory with displays of force (chimpanzees for example have lots of display of force rituals, specially around selecting leadership, I believe) and sometimes non-lethal conflict (some species evolve apparatus just for this kind of conflict, e.g. antlers, so they can engage in conflict with low chance of injury).

Since we're referring to human cultures, something distinct we have is memory and communication -- information can get out on reputation, behavior, etc. of a group. I think if a group just goes out and murders another in their sleep (which TBF is not so easy), then I imagine for example word would also go out of their actions and may get into trouble with other groups, I'm sure spiritual traditions would also have a say about it, in favor of some sort of "spiritual revenge". But I suppose it's difficult to generalize.

I do think it's interesting to consider some forms of morality, or just metaphysical and logical understanding around ethics, as a kind of technology that enables people to live longer and enable more secure conditions, including preventing large scale conflict that can bring destruction on an industrial scale to entire societies (although misguided moral arguments ironically are also misused sometimes to enact destruction). Although I guess morality alone is not enough (because not everyone seems to internalize it well), and other mechanisms are also helpful to achieve more social stability.

(Also of note is that there can be such thing as too much stability -- for example, for some new more interesting and maybe more worthwhile forms of culture to emerge, old ones have to be replaced, so stability should be balanced with cautious openness to new ideas, technologies, methods, peoples (ethnicity), cultures, ..., and worldviews -- of course, as long as change is in the direction of improving our lives collectively. For example in some cases religious fundamentalism advocates for an absolutist cultural stagnation; we just shouldn't need one group to murder another to spread about new things)

> There’s no mechanism that helps the process of evolution select for the survival or reproduction of the species

The "mechanism" is just the process of evolution itself, and how it plays out in practice, e.g. via punctuated equilibrium.

Over shorter timespans the gene pool of a breeding population incrementally drifts according to the success of individual genetics, but then once in a while, over multiple generations, something in the environment (disease, food, competition, etc) may change quickly and the gene pool as a whole, not just that of individuals, is thereby tested, with accumulations of previously benign changes sometimes suddenly becoming critical. In this way evolution is acting on the entire gene pool - of the species or more correctly of that interbreeding sub-population.

Success in evolution, the ability of the species as a whole to adapt and compete, also requires genetic diversity, not only to avoid inbreeding, but also to provide species level resilience, and species level ability to quickly adapt. e.g. It seems that the success of sexual reproduction is because it is a way to "game the game" by increasing genetic diversity and therefore improve along these axis of resilience and fast adaptation.

There are also social species, such as ourselves, where the social group becomes port of the individuals environment, and genetics best-fitted-to-the-environment becomes a group dynamic.

Fighting to the death and mating are not the same!

There are a number of species where the female eats the male after mating - examples such as praying mantis and octopus. Both octopus males and females die after mating, the female after having protected the eggs, so it makes sense that she sometimes eats the male too (who is going to die anyway). But, examples like this are relatively rare, and for species specific reasons.