Given that they most famously turn up in social insects (where the genetics are all bent out of shape in just the simple obvious way to solve the instability problem) and in the one species with an enormous Dunbar number, the enormous-Dunbar-number case is probably not simple. (Game theory of limited information, intentional deception, strategic thinking, intentional signaling, bounded rationality, etc. is not, among most people who have thought seriously about it, considered to be easy. I like David Friedman’s take on it: “Problems that stumped John von Neumann go at the bottom of my pile.”)

Graham, social science is often trolling you or just sneeringly speaking power to truth. But this is a real puzzle, not just a propagandist coyly refusing to use the word “tribalism”. It is not a puzzle like black body radiation or the Michelson-Morley experiment ca. 1900 indicating a problem with our fundamental laws of the universe, but it is a puzzle like turbulence or protein folding or the relativistic many-body quantum mechanics of high temperature superconductors or nitrogenase where the known fundamental laws of the universe explode into an incredibly nasty problem of analysis if you try to understand the problem at a useful level of accuracy.

In many other circumstances social scientists merrily speak power to truth by e.g. refusing to consider obviously relevant fundamental rules of the universe like DNA heritability in screamingly obvious situations like kids turning out like their parents. In this case, though, the one who seems to be trolling you is Grurray, writing as though using a name like ‘tribalism’ or ‘turbulence’ or ‘catalysis’ is an explanation in a context where people are in fact trying to understand the phenomenon of turbulence or catalysis or (stably naturally selected) tribalism.

So the question remains: why are people tribal? Why would someone sacrifice themselves for the race, nation or tribe?

Perhaps it is similar to religion. People sacrifice themselves for ideas, religions and ideologies. The nation is an idea like these.

There are hypotheses that religion is beneficial to fitness, but dying for it seems to be an aberration. In that case it seems to be a mind-virus, a morbid meme.

I expect the true explanations for the mysteries of group selection, altruism and mass warfare, will turn out to be linked.

The reason is they have no one to reproduce with because of polygamy, so they fight and die.

In hunter-gatherer societies men participate more in child rearing and family, have less time or need to fight, and they’re testosterone decreases. In pastoral societies men are less needed to invest in child rearing because of the climate and environment, and they have more requirements for roaming. Polygamy, higher testosterone, and fighting results.