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THE ORIGIN OF INTELLIGENCE Many theories have been proposed as to why humans developed greater intelligence, going all the way back to Charles Darwin. According to one theory, the evolution of the human brain probably took place in stages, with the earliest phase initiated by climate change in Africa. As the weather cooled, the forests began to recede, forcing our ancestors onto the open plains and savannahs, where they were exposed to predators and the elements. To survive in this new, hostile environment, they were forced to hunt and walk upright, which freed up their hands and opposable thumbs to use tools. This in turn put a premium on a larger brain to coordinate tool making. According to this theory, ancient man did not simply make tools—“tools made man.” Our ancestors did not suddenly pick up tools and become intelligent. It was the other way around. Those humans who picked up tools could survive in the grasslands, while those who did not gradually died off. The humans who then survived and thrived in the grasslands were those who, through mutations, became increasingly adept at tool making, which required an increasingly larger brain. Another theory places a premium on our social, collective nature. Humans can easily coordinate the behavior of over a hundred other individuals involved in hunting, farming, warring, and building, groups that are much larger than those found in other primates, which gave humans an advantage over other animals. It takes a larger brain, according to this theory, to be able to assess and control the behavior of so many individuals. (The flip side of this theory is that it took a larger brain to scheme, plot, deceive, and manipulate other intelligent beings in your tribe. Individuals who could understand the motives of others and then exploit them would have an advantage over those who could not. This is the Machiavellian theory of intelligence.) Another theory maintains that the development of language, which came later, helped accelerate the rise of intelligence. With language comes abstract thought and the ability to plan, organize society, create maps, etc. Humans have an extensive vocabulary unmatched by any other animal, with words numbering in the tens of thousands for an average person. With language, humans could coordinate and focus the activities of scores of individuals, as well as manipulate abstract concepts and ideas. Language meant you could manage teams of people on a hunt, which is a great advantage when pursuing the woolly mammoth. It meant you could tell others where game was plentiful or where danger lurked. Yet another theory is “sexual selection,” the idea that females prefer to mate with intelligent males. In the animal kingdom, such as in a wolf pack, the alpha male holds the pack together by brute force. Any challenger to the alpha male has to be soundly beaten back by tooth and claw. But millions of years ago, as humans became gradually more intelligent, strength alone could not keep the tribe together.
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Michio Kaku (The Future of the Mind: The Scientific Quest to Understand, Enhance, and Empower the Mind)