Francisco Gil-White and Peter Richerson have an entry in The Encyclopedia of Cognitive Science titled Large-scale human cooperation and conflict (PDF). The authors reject both kin selection and reciprocal altruism as sufficient to explain the size of human groups. They assume that genetic relationships drop off too quickly for kin selection to spread a very wide net (and ask why other mammals do not seem to coalesce into the same complex social groups if kin selection is operative among them) and assert that reciprocal altruism models fail to scale up well beyond a dyad (that is, two interacting individuals).

Their solution? They propose a cultural group selection model which incoorperates gene-culture coevolution into a feedback loop. I emphasize the cultural aspect because the authors make it clear that they are not proposing a genetic group selective model. Some of the same tendencies that we have been discussing in the context of ethnic (genetic) nepotism and tribalism are brought out as proximate mechanisms to facilitate group cohesion (social markers, dress and language), but they also emphasize the importance of imitation in effecting large scale group conformity over a short period of time and maintaining intergroup variance. Once the idea of cultural trait groups is in place they propose that selection occurred between these groups via intergroup comeptition (a functionalist perspective). Additionally, particular behavorial traits that facilitated smooth operation and mobilization of large social unit were favored within these groups , that is, our cognitive biases & social intelligence were shaped by the groups of the EEA. In earlier posts I assumed that reciprocal altruism served as the glue for the 100-150 individuals who bonded into the atomic units, but I suppose that the process that is sketched out in the paper above explains the cohesive action of a Roman century at least as well.

But, they end with this muddle:

It is important to note that the above is insufficient for an explanation of, say, racial conflict. For most of history the antagonistic political units have often not been maximal ethnic unites, but rather smaller (e.g. sub-ethnic tribes, clans) or larger (e.g. multi-ethnic chiefdoms, empires) units...We are still very far from understanding how and why ideologies such as ethno-nationalism spread and remain stable, and why they are so easily exportable into vastly different cultures....

Hm. How important has racial conflict on the grand scale of war? I would submit that most conflicts have been aracial in nature. I recall seeing a painting from the late 19th century heyday of white racial solidarity which depicted the European powers (in the form of female valkyries) standing on a cliff's edge and confronting vast yellow hordes. Germany was depicted as attempting to persuade a reluctant Britain to join in the great defense of Europe from racial aliens. Why was Britain reluctant? The caption suggested that was because of the tacit alliance between Britain and Japan! This, during an age when the supposed 'natural' race-loyalty of European man was hitched to an explicit racialist ideology in most of the West!¹

Also, let us recall that though we should stand in awe of the British conquest of their Empire, a small island nation ruling 1/4 of the world, much of the conquering was done by local armies who fought under British officers (or sometimes half-caste ones as in India). Some have suggested that lack of racial solidarity is a peculiarly white afflication, but tell that to the Marathas or Sikhs who had to face Bengali and Tamil sepoys who willingly fought for the British East India Company. And tell that to the Bengali and Tamil soldiers who rebelled against the British, ostensibly for the Mughal Emperor, and suffered the wrath of Sikh sepoys who extracted their revenge for humiliations wrought decades earlier.

There are many confusing questions that give rise to more complex ones. I don't know if I'm convinced of any of the models out there at this point. But, if you want to read more about cultural evolution from this angle, that is gene-culture coevolution, check out Peter Richerson's site.

1 - Racial solidarity wasn't the only thing that was difficult to follow through on transnationally, the Ottomans were propped up by the British and French against the fellow Christian power of Russia during this age of muscular Christianity.