In reading the book The Happiness Hypothesis by Jonathan Heidt I came across an important element that makes ultrasocial societies work - reciprocity.
Heidt defines ultrasociality as: living in large cooperative societies in which hundreds of thousand of individuals reap the benefits of an extensive division of labor. Only four instances of ultrasociality are in existence - among hymenoptera (ants, bees and wasps), termites, naked mole rats, and humans. In all species but humans the force that makes that possible is the genetics of kin altruism. In an ants nest or a bee nest, everybody is brother and sister, and since you have as much genes in common with your siblings as you have with your children, the evolutionary drive to leave surviving copies of your genes makes those ultrasocial communities work - shared genes equals shared interest.
In societies that are not structured like bee or ant colonies, the shared set of genes that you have with others drops off rather dramatically - while you share 50% of the genes with your children and siblings, you only share 1/8 the genes with your cousins, and 1/32 with second cousins. In a strictly Darwinian calculation, you would only spend as much energy to save 4 of your cousins as you would for 1 child or brother. That is why kin altruism explains only how groups of a few dozen, or perhaps a hundred, animals can work together. The rest would be competitors in the Darwinian sense.
So what happened to human societies? How did we get fictitious families, like the Mafia, where there is no real kinship, even though they talk about the Godfather and being part of the "family", to work as ultrasocial societies? It's the old fashioned "you scratch my back and I'll scratch yours" phenomenon - which is in fact a mindless and automatic reciprocity reflex. if someone receives a favor, that person will be driven to repay that favor - not because it the proper thing to do - but because it is a built-in ethological reflex. It's tit-for-tat, hardwired in our brains, that opens the possibility of forming cooperative relationships with strangers. Now mind you that tit-for-tat can only explain the existence of social groups up to a few hundreds. What allows larger social groups is its co-existence with vengeance, gratitude and gossip as tools that reduce the payoff to cheaters by the cost of making enemies.
Those very primitive hardwired human behaviors confirm a lot about what makes online communities work as well - the importance of reputation, the importance of self-organized posses to police communities, the importance of helping one another as a currency, and the failure of communities where reciprocity is not an integral component of the community.
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