Читать книгу Green Earth - Kim Stanley Robinson - Страница 26

Let’s rehearse what we know about who we are.

We are primates, very closely related to chimps and other great apes. Our ancestors speciated from the other apes about five million years ago, and evolved in parallel lines and overlapping subspecies, emerging most clearly as hominids about two million years ago.

East Africa in this period was getting drier and drier. The forest was giving away to grassland savannahs dotted with scattered groves of trees. We evolved to adapt to that landscape: the hairlessness, the upright posture, the sweat glands and other physical features. They all made us capable of running long distances in the open sun near the equator. We ran for a living and covered broad areas. We used to run game down by following it until it tired out, sometimes days later.

In that basically stable mode of living the generations passed, and during the many millennia that followed, the size of hominid brains evolved from about 300 cubic centimeters to about 1200 cubic centimeters. This is a strange fact, because everything else remained relatively stable. The implication is that the way we lived then was tremendously stimulating to the growth of the brain. Almost every aspect of hominid life has been proposed as the main driver of this growth, everything from the calculation of accurate rock throwing to the ability to dream, but certainly among the most important must have been language and social life. We talked, we got along; it’s a difficult process, requiring lots of thought. Because reproduction is crucial to any definition of evolutionary success, getting along with the group and with the opposite sex is fundamentally adaptive, and so it must be a big driver of increasing brain size. We grew so fast we can hardly fit through the birth canal these days. All that growth from trying to understand other people, the other sex, and look where we are.