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Bigger is smarter is better. That's the conventional wisdom for why the human brain gradually became three times larger than the ancestral brain.
"But bigger brains were not generally smarter brains," said neurobiologist William H. Calvin at the American Association for the Advancement of Science meeting in Washington, D.C. on Friday, Feb. 18. "Thanks to the archaeologists, we know that our ancestors went through two periods, each lasting more than a million years, when toolmaking techniques didn't gradually improve, despite a lot of gradual brain size increase."

There is no lack of other candidates for why a bigger brain would be better. Calvin, who is affiliate professor of psychiatry and behavioral sciences at the University of Washington in Seattle, emphasized the detailed planning needed as you get set to throw. "In hunting, you have to be right the first time, or dinner runs away, but there are other strong candidates such as the brain space needed to use words in short sentences," noted Calvin. "You need something similar for extensive sharing. You have to keep track of who owes what to whom, so as to avoid cheaters. And that's a task similar to saying who did what to whom."

The problem is that, whatever the drivers were, they didn't produce a general cleverness that showed up in toolmaking techniques. What's even worse for the bigger-is-smarter-is-better hypothesis, Calvin said, is that after Homo sapiens was walking around Africa 200,000 years ago with a brain of our size, we spent ?with a few exceptions ?the next 150,000 years doing more of the same.

"So bigger is better may be true for something, say the big payoffs associated with protolanguage or sharing or accurate throwing," he said. "But for long periods in human evolution, general intelligence may not have improved very much."

Yet when it finally did, the results were spectacular. Starting back about 75,000 to 50,000 years ago in Africa, there was a burst of creativity. Necklaces and pendants appear first, then figurines. By 35,000 years ago, there were paintings on the walls of European caves, complete with perspective.

"This creativity probably marks the emergence of the whole suite of higher intellectual functions, each of which requires some structuring to fit everything together," he said.

Most obvious is syntax, the clues that make long sentences possible. Other aspects of intellect include multi-stage planning, chains of logic, games with arbitrary rules, and our fondness for discovering hidden patterns.

"This search for how things hang together is what's seen in doing jigsaw and crossword puzzles, in doing science, and in getting the joke," Calvin explained. "It's likely that they all are sharing some neural machinery for handling structure and judging coherence. Improve one by natural selection, and you may improve the others too. The free lunch is alive and well in biology."

Those functions were really new uses for old things, Calvin said, probably the brain mechanisms for structuring movements. The difficulty came with controlling the quality of the novel behaviors, he explained.

"You have to resolve the ambiguities and improve the quality of the ensemble offline, to make sure it hangs together, before you act on it," Calvin said. "You do that many times a day, whenever you speak a sentence you've never spoken before."

It is that combination of structured thought and improving its quality that, he believes, is what human levels of contemplative consciousness are all about.

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