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Balkan endemic kidney disease surfaced in the 1950s and for decades defied attempts to finger the cause. It occurred...
The Pyrenean ibex, an impressive mountain goat that lived in the central Pyrenees in Spain, went extinct in 2000. But a...
Tight budgets are forcing NASA to consider turning off one or more planetary science projects that have completed their...
Ebola is not a stranger to West Africa—an outbreak in the 1990s killed chimpanzees and sickened one researcher. But the...
In an as-yet-unpublished report, an international panel of geoscientists has concluded that a pair of deadly...
Tropical disease experts tried and failed before to eradicate yaws, a rare disfiguring disease of poor countries. Now,...
Since 2002, researchers have reported that agricultural communities in the hot and humid Pacific Coast of Central...
- 10 April 2014 11:44 am , Vol. 344 , #6180
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Making Sense of Big Brains
9 May 2001 7:00 pm
Small-minded! Pinhead! Peabrain! The insults people hurl reveal our assumptions about what makes us intelligent. But two new studies in the 10 May issue of Nature suggest that it's not just brain size that makes us smart. Instead, we higher primates have brains with a distinctive design that allows us to think big.
Most human intelligence resides in our overgrown neocortex, the convoluted outer layer of the brain that helps us make sense of the world. Scientists have argued for years about how our neocortex got so big. Some say that higher primates evolved a new brain plan, perhaps in response to evolutionary pressure to develop complex social skills. Others contend that the basic primate brain plan hasn't changed that much compared to other mammals; our big neocortex developed incidentally when our brain had to grow big enough to control a big body.
To track how brain plans differ in primates and other mammals, neuroscientist Sam Wang of Princeton University and colleagues scrutinized the relative volumes of 11 brain regions. First, they calculated the fraction of the brain volume each region occupies in 75 species. Then the researchers turned the 11 relative volumes into an overall measure of brain composition called a cerebrotype. Groups of closely related species, such as lemurs or higher apes, had similar cerebrotypes. This means that brain structures, like bones or other tissue, can be used to deduce evolutionary relationships, the researchers suggest.
The second new study could help explain why the neocortex grew disproportionately large in humans. By examining data on brain size and brain cell density from 23 higher primates, neurobiologist Chuck Stevens of the Salk Institute in San Diego showed that the sharper a primate's vision, the more cortex it devotes to processing images. That is, the number of cells in the visual cortex is proportional to the number of cells lower down in the visual system raised to the power of 3/2. A similarly unbalanced increase in cortex size relative to simple sensations could account for enlarged language, hearing, and motor cortex as well, Stevens says.
The cerebrotype study is "important work" that suggests parts of the brain have in part evolved independently, says neuroscientist Jon Kaas of Vanderbilt University. And he adds that the visual system study provides a "good argument" that explains why the human neocortex evolved to grow so big.