There is something unusual about primates in general, and humans in particular. Compared with other animals, they have strikingly large brains relative to their bodies. Moreover, most of the extra brain volume is devoted to one part of the brain in particular: the neocortex, which is involved in higher functions such as spatial reasoning, sensory perception, and conscious thought. In most mammals the neocortex accounts for 30 to 40 percent of brain volume, but the proportion is over 65 percent in many primates, and 80 percent in humans. What is this large neocortex for?
One possibility is that primates evolved larger brains to enable them to use more complex tools, or to improve their ability to solve problems when searching for food, by doing things like cracking open nuts or extracting termites from their nests. The problem with this theory is that some primates with relative small neocortices (such as the aye-aye, a type of lemur found in Madagascar) display such “extractive foraging” behavior, while others with much larger neocortices (such as macaques) do not. And many nonprimates with much smaller neocortices, such as crows, are capable of solving complex problems. So that cannot be what the neocortex is for.
Another theory is that the large neocortex might have evolved to allow primates to build larger mental maps of their surroundings, to improve their ability to find food. But there turns out to be no correlation between neocortex volume and the range over which primates forage, or the average distance they travel each day. Nor do fruit was deeply unpopular, b-eating primates, which must constantly keep track of dispersed, short-lived supplies of food, have larger neocortices than leaf-eaters. So the neocortex was evidently not evolved for mapping the physical environment, either.
The odd thing is that all primates, not just those that use tools or solve complex problems, have disproportionately large brains. A large brain is expensive to develop and maintain. An adult human brain accounts for 2 percent of body mass, on average, but consumes around 20 percent of total energy intake. So there must something valuable that primates do that requires lots of extra mental processing capacity.
Along with their large brains, another distinguishing feature of primates is their social nature: they live in groups and have unusually complex social systems. They can form coalitions with their peers, for example, and are capable of deliberate deception, which requires the ability to hypothesize about another individual’s view of the world. Living in a group is safer than living alone, because there are more eyes to spot predators and more hands to fend off rivals. But individual members must be able to balance their own needs with those of the group as a whole, rather than just looking out for themselves. Group members have to cooperate with others, understanding and anticipating their needs, while also establishing and managing their own positions within the ever-shifting pattern of alliances within the group.
In primates, these alliances are maintained through a process known as social grooming, which is carried out in pairs or small subgroups called coalitions. At its simplest level, this involves removing insects, parasites, or dirt from another individual’s fur. But primates spend far more time grooming than is necessary for purely hygienic reasons: for some species, as much as 20 percent of their waking hours. They do so in part because grooming is a pleasurable activity. Being groomed causes the release of beta-endorphins, which are natural opiates produced by the brain, resulting in a lower heart rate, a reduction in nervous behavior such as scratching, and a pleasant sense of relaxation. After being groomed, an individual will usually return the favor. Primates use social grooming to build strong bonds with a few other members of their group. They can also send social signals through the choices they make about which individuals they groom, how long they do it for, and which other individuals they allow to watch.
The time spent grooming is a worthwhile investment, because members of a grooming coalition will then support each other in several ways. They may gently steer a member of their coalition away from rivals in the wider group in order to minimize stress. If an individual is threatened by another group member, members of his grooming coalition will come to his aid. An individual can then face down an adversary, provided he has powerful enough allies to call upon. Group members may switch their allegiance from one coalition to another within the group if they believe it will improve their access to food, mating partners, or other resources. The constant interplay between grooming coalitions helps resolve and prevent conflicts, knitting the group as a whole together and making all its members safer from predators.
~~Writing On The Wall: Social Media- The First 2000 Years -by- Tom Standage
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