The Limits of Intelligence

The laws of physics may well prevent the human brain from evolving into an ever more powerful thinking machine

By Douglas Fox

Image: Photograph by Adam Voorhes

In Brief
  • Human intelligence may be close to its evolutionary limit. Various lines of research suggest that most of the tweaks that could make us smarter would hit limits set by the laws of physics.
  • Brain size, for instance, helps up to a point but carries diminishing returns: brains become energy-hungry and slow. Better “wiring” across the brain also would consume energy and take up a disproportionate amount of space.
  • Making wires thinner would hit thermodynamic limitations similar to those that affect transistors in computer chips: communication would get noisy.
  • Humans, however, might still achieve higher intelligence collectively. And technology, from writing to the Internet, enables us to expand our mind outside the confines of our body.

Santiago Ramón y Cajal, the Spanish Nobel-winning biologist who mapped the neural anatomy of insects in the decades before World War I, likened the minute circuitry of their vision-processing neurons to an exquisite pocket watch. He likened that of mammals, by comparison, to a hollow-chested grandfather clock. Indeed, it is humbling to think that a honeybee, with its milligram-size brain, can perform tasks such as navigating mazes and landscapes on a par with mammals. A honeybee may be limited by having comparatively few neurons, but it surely seems to squeeze everything it can out of them.

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