Book review of Robin Dunbar

Robin Dunbar:
GROOMING, GOSSIP AND THE EVOLUTION OF LANGUAGE (Faber and Faber, 1996)

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The British psychologist Robin Dunbar believes that language was not invented for communication but as a more efficient form of grooming, which in turn functioned to cement society.
All primates live in groups. The size of a primate's neocortex, as compared to the body mass, is directly proportional to the size of the average group for that primate. Humans tend to live in the larger groups of primates, and human brains are correspondingly much larger.
Dunbar studied how brain size determines social size and why. Every species has a cognitive limit to the number of individuals with whom any one individual can maintain stable relationships. That number for humans is about 150. Generally speaking, the bigger the brain (the neocortex) the higher the number of relationships among objects that the brain can handle. Each species has a natural limit to how much its brain can "correlate".
As humans transitioned from the forest to the savannah, they needed to band together in order to survive the increased danger of being killed by predators. Language helped keep large groups together. Thus humans who spoke had an evolutionary advantage (the group) over humans who did not develop that skill. Dunbar believes that human speech is simply a more efficient way of "grooming": apes cement social bonds by grooming the members of their group. Humans "gossiped" instead of grooming each other. Later, and only later, humans began to use language also to communicate information. Dunbar believes that dialects developed for a similar reason: to rapidly identify members of the same group (it is notoriously difficult to imitate a dialect)
Basically, in order to avoid being eaten by predators, humans needed to band together, and that required bigger brains.
Language and societies evolved together: society stimulated the invention of language, and language enabled larger societies, that stimulated even more sophisticated languages, that enabled even larger societies, etc.