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Did human intelligence peak thousands of years ago?

        Science | Evolution

According to at least one Stanford geneticist, humans have been on a cerebral backslide with the rise of modern agriculture and the loss of many hunter-gatherer societies. See our image gallery of genetics at work.
According to at least one Stanford geneticist, humans have been on a cerebral backslide with the rise of modern agriculture and the loss of many hunter-gatherer societies. See our image gallery of genetics at work.
© Martin Harvey/CORBIS

For years, researchers, politicians and cranky uncles have held forth on the source of society's looming downfall. Comic books and pulps rot our brains, television is a vast wasteland and the Internet scatters our senses [source: Carr]. Now, just when matters couldn't sound any direr, along comes geneticist Gerald Crabtree of Stanford University to tell us that civilization itself is killing our cognition and extinguishing our emotional stability.

It's enough to make you want to watch "Idiocracy" and drink Brawndo all day.

But perhaps we're getting ahead of ourselves. After all, attempts to unravel the genetics woven into intelligence predate Gregor Mendel's work on plant hybrids, yet we remain in the early stages of the science. Meanwhile, related fields continue their century-long struggle to disentangle intelligence's many definitions, measurements and influences.

Perhaps that's why Crabtree's idea sounds, to many scientists' ears, a bit impudent.

The Stanford geneticist thinks human intelligence is a fragile business, less a robust network and more a genetic Rube Goldberg machine. Unless its components -- a Crabtree-estimated group of 2,000-5,000 key genes -- are intensely selected for in a population, the generation-by-generation buildup of detrimental mutations will doom us to dimness. By his calculations, we've been on a cerebral slide ever since we discovered agriculture and began to form sedentary societies [sources: Crabtree; Crabtree].

According to Crabtree, a hunter-gatherer paid the ultimate penalty for folly by either starving or becoming lion chow. Today's blundering businessperson seems to bear out the Peter Principle by failing upward, getting rich, acquiring a mate and passing on rather baseline brainpower to their children [sources: Crabtree; Crabtree].

To some colleagues, however, this hypothesis has more holes than a ... really, really holey thing. They point out that, on top of the hitches facing any sweeping genetic-intelligence hypothesis -- unclear genetic links, uncertain environmental roles and so on -- Crabtree's big idea has a significant scientific snag: It not only lacks proof, it also lacks any clear means of being proven [sources: Britannica; Chabris et al.; Connor]. As such, it's less a hypothesis and more an interesting notion.

Regarding society's alleged negative influence, writes neural geneticist Kevin J. Mitchell of the Smurfit Institute of Genetics, "No evidence is offered for this idea, which contradicts models suggesting just the opposite: that the complexities of social interactions in human societies were a main driver of increasing intelligence" [source: Mitchell].


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