Free Last Ape Standing: The Seven-Million-Year Story of How and Why We Survived by Chip Walter Page B

new ability had on human evolution and has each day on your life and mine. The farther down the evolutionary chain creatures fall, the less complex their brains are as a rule, and the less they are shaped by their personal experience, which is another way of saying that their day–to–day actions are largely, if not entirely, governed by their genes, rather than by anything we might call a “self.”
    Moths, for example, are drawn to candle flames because they are genetically programmed to navigate by the light of the moon. Not having much of a brain, they have been known to mistake a flame for the moon and get incinerated for their trouble. This happens not simplybecause their brain is small, but because it is also hardwired by its genes and not readily able to learn from experience.
    For hundreds of millions of years genes were a perfectly effective, if plodding and random, way of adapting to changes in environment, but it wasn’t efficient. It took a long time for evolution to get around to building a brain that could think, even a little, for itself. But once it did, those animals blessed with one tended to survive longer than those that weren’t. Brains are more resourceful than trial–by–error genetics. They map the world in real time and increase the chances that you will make a lifesaving decision on the spot rather than a deadly, DNA–dictated one that isn’t even aware you
are
on the spot. Not that the influence of genes versus brains is either/or. All creatures endowed with a brain lie along a continuum of cerebral, and therefore behavioral, flexibility. There are no hard boundaries. But the
degree
of that hardwiring in many ways marks the difference between, say, a flat–worm, and us.
    The impact that the outside world can have on our brains during our childhood explains how seven billion of us can be walking the planet every day, each a thoroughly unique universe unto ourselves, distinct in personality, experience, thought, and emotion; yet similar enough that we can (more or less) relate to one another and be counted as members of the same species. What has been far less clear, and a slippery problem for scientists, has been exactly how the genetic commands we inherit from our parents are bent by the unique relationships and events in our lives. It turns out several forces are at work. Very hard at work. 4
    In the first three years of life the human cerebral cortex triples in size. This is like nothing else in nature. Yet it isn’t simply the growth of neurons that makes the human brain so powerful. It is also the way it feverishly links them up. Why should this matter? Think of the brain as a miniature, though considerably more complex, Internet, compressed in size and time. Each neuron is like a computer sitting on a lap or desk somewhere. Computers today are powerful, like neurons, and can by themselves accomplish a great deal. I am writing this book on one right now. But connect neurons or computers to one another, and they become amplified and add up to far more than the sum of their parts. When my computer links to the Internet, it enables me toresearch information I use in the book, share passages I am writing with others in a blink, and gather opinions, thoughts, and insights by engaging in any number of conversations. I can instantly track down specific bits of information I need or download facts, maps, images, even whole books and movies. By branching out and communicating in all directions, my computer becomes, in many ways, all the computers it can touch. Now multiply this by millions of sites from Facebook to the Library of Congress, billions of Web pages, and innumerable other computers, and you begin to get a feel for the benefits of interconnecting neurons in the brain. There is power in communication.
    The pathways between neurons begin to radiate almost the moment nerve cells undertake their growth in the fetal brain. Yet while the proliferation of neurons begins to slow at age