Superficially, the claim that culture-level group selection has created DNA-level social instincts supporting human ultrasociality is a strange one.
There's a much simpler and better hypothesis that explains why culture has promoted human ultrasociality that arose over a decade ago from within memetics. The idea is that memes need humans to get in contact with one another in order for them to reproduce. The hypothesis is covered on the page: Memes and the evolution of human ultrasociality.
The idea proposes straight-forward individual-level benefits to social behaviour with other humans - namely:
- Ultrasocial individuals acquire more memes (and organic symbionts), and these are (on average) good.
- Ultrasocial individuals get to influence others with their memes (and organic symbionts) more - spreading their own influence in the process, and gaining reputation and status credits that can be cashed in later.
Now it may be that these benefits don't outweigh the costs of some forms of altruism - but such expensive altruism is rare, and can be explained well by virtue signalling, over-generalisation and cognitive resource limitation.
There's very little need to invoke cultural group selection, it seems. There is little sign of phenomena that require explanations based on high-level selection. It is not clear why is the literature in the area is so full of such explanations - when there is a much simpler and more obvious hypotheses on the table.
- Mesoudi, Alex & Jensen, K. (2010) Culture and the evolution of human sociality. In: The Oxford Handbook of Comparative Evolutionary Psychology, edited by J. Vonk & T. Shackelford. Oxford, UK: Oxford University Press.