Steven Pinker -- How the Mind Works - Hampshire High Italian ...

194 | HOW THE MIND WORKSsocial, intelligence. In a species that runs on information, each facultymultiplies the value of the others. (Incidentally, the expansion of thehuman brain is no evolutionary freak crying out for a runaway positivefeedback loop. The brain tripled in size in five million years, but that isleisurely by evolutionary timekeeping. There was enough time inhominid evolution for the brain to shoot up to human size, shrink backdown, and shoot up again several times over.)A third pilot of intelligence, alongside good vision and big groups, isthe hand. Primates evolved in trees and have hands to grasp thebranches. Monkeys use all four limbs to run along the tops of branches,but apes hang from them, mainly by their arms. They have put their welldevelopedhands to use in manipulating objects. Gorillas meticulouslydissect tough or thorny plants to pick out the edible matter, and chimpanzeesuse simple tools such as stems to fish out termites, rocks to bashopen nuts, and mashed leaves to sponge up water. As Samuel Johnsonsaid about dogs walking on their hind legs, while it is not done well, youare surprised to find it done at all. Hands are levers of influence on theworld that make intelligence worth having. Precision hands and precisionintelligence co-evolved in the human lineage, and the fossil recordshows that hands led the way.Finely tooled hands are useless if you have to walk on them all thetime, and they could not have evolved by themselves. Every bone in ourbodies has been reshaped to give us our upright posture, which frees thehands for carrying and manipulating. Once again we have our ape ancestorsto thank. Hanging from trees calls for a body plan that is differentfrom the horizontal four-wheel-drive design of most mammals. Apes'bodies are already tilted upward with arms that differ from their legs, andchimpanzees (and even monkeys) walk upright for short distances tocarry food and objects.Fully upright posture may have evolved under several selection pressures.Bipedal walking is a biomechanically efficient way to retool a treehangingbody to cover distance on the flat ground of the newly enteredsavanna. Upright posture also allows one to peer over grass like a marmot.Hominids go out in the midday sun; this zoologically unusual workshift brought in several human adaptations for keeping cool, such ashairlessness and profuse sweating. Upright posture might be another; itis the opposite of lying down to get a tan. But carrying and manipulationmust have been crucial inducements. With the hands free, tools couldbe assembled out of materials from different locations and brought to