This is by no means an overnight phenomenon.
Scholars at Oxford have refuted the notion that all mammals over time developed larger brains. Instead Dr. Susanne Shultz and Prof. Robin Dunbar found over a span of 60 million years that more social creatures, among them humans, had the most rapidly expanding brain sizes to cope with the complexity of collaboration, social norms and coordination.
“The research team analysed available data on the brain size and body size of more than 500 species of living and fossilised mammals. It found that the brains of monkeys grew the most over time, followed by horses, dolphins, camels and dogs. The study shows that groups of mammals with relatively bigger brains tend to live in stable social groups. The brains of more solitary mammals, such as cats, deer and rhino, grew much more slowly during the same period.”
They noted that the fact that cats’ brains did not expand while dogs’ and horses’ brains did, can be accounted for by the far more solitary lives that cats lead in relation to dogs and horses, which interact far more with humans.
Obviously, since these evolutionary anthropologists couldn’t go back in time to distinguish social cavemen from more solitary cavemen, it is impossible to tell whether the expansion of brain size was related to the average levels of socialization of a species or whether this same pattern would have held true at the individual level: with offspring of more social parents having larger brains than offspring of less social humans.
Nonetheless, food for thought… The implication: get out and socialize and help our species to continue to grow our average brain size, although the results may not be noticeable within your lifetime.
The study is called “Encephalization is not a universal macroevolutionary phenomenon in mammals but is associated with sociality” (PNAS Journal, November 30, 2010, by Susanne Shultz and Robin Dunbar). Abstract here.
Shultz and Dunbar’s center, Oxford University’s Institute of Cognitive and Evolutionary Anthropology, is here.