Cosmos - Carl Sagan [148]
The information content of the human brain expressed in bits is probably comparable to the total number of connections among the neurons—about a hundred trillion, 1014, bits. If written out in English, say, that information would fill some twenty million volumes, as many as in the world’s largest libraries. The equivalent of twenty million books is inside the heads of every one of us. The brain is a very big place in a very small space. Most of the books in the brain are in the cerebral cortex. Down in the basement are the functions our remote ancestors mainly depended on—aggression, child-rearing, fear, sex, the willingness to follow leaders blindly. Of the higher brain functions, some—reading, writing, speaking—seem to be localized in particular places in the cerebral cortex. Memories, on the other hand, are stored redundantly in many locales. If such a thing as telepathy existed, one of its glories would be the opportunity for each of us to read the books in the cerebral cortices of our loved ones. But there is no compelling evidence for telepathy, and the communication of such information remains the task of artists and writers.
The brain does much more than recollect. It compares, synthesizes, analyzes, generates abstractions. We must figure out much more than our genes can know. That is why the brain library is some ten thousand times larger than the gene library. Our passion for learning, evident in the behavior of every toddler, is the tool for our survival. Emotions and ritualized behavior patterns are built deeply into us. They are part of our humanity. But they are not characteristically human. Many other animals have feelings. What distinguishes our species is thought. The cerebral cortex is a liberation. We need no longer be trapped in the genetically inherited behavior patterns of lizards and baboons. We are, each of us, largely responsible for what gets put into our brains, for what, as adults, we wind up caring for and knowing about. No longer at the mercy of the reptile brain, we can change ourselves.
Most of the world’s great cities have grown haphazardly, little by little, in response to the needs of the moment; very rarely is a city planned for the remote future. The evolution of a city is like the evolution of the brain: it develops from a small center and slowly grows and changes, leaving many old parts still functioning. There is no way for evolution to rip out the ancient interior of the brain because of its imperfections and replace it with something of more modern manufacture. The brain must function during the renovation. That is why our brainstem is surrounded by the R-complex, then the limbic system and finally the cerebral cortex. The old parts are in charge of too many fundamental functions for them to be replaced altogether. So they wheeze along, out-of-date and sometimes counterproductive, but a necessary consequence of our evolution.
In New York City, the arrangement of many of the major streets dates to the seventeenth century, the stock exchange to the eighteenth century, the waterworks to the nineteenth, the electrical power system to the