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Why Big Brains Are Better

14 March 2005 (All day)
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Well-traveled. The feral pigeon adapts easily to new locales and ecological niches--an ability that is closely related to relative brain size.

When it comes to brains, it seems evident that bigger is better. But scientists are still debating just what the evolutionary benefit of having a big brain really is. Now, a study across a range of bird species suggests that a larger brain may confer at least one important advantage: being better able to survive in new, non-native environments.

Compared to nearly all other mammals, including our primate cousins, we humans have the greatest brain size relative to our body mass. As for why, one popular hypothesis holds that enlarged brains--not just in humans but in other animals as well--are an adaptation to new or changed environmental conditions. Yet there has been little firm evidence for this idea.

So recently an international team of researchers set about testing this hypothesis in birds, a class of animals with widely varying habitats and relative brain sizes. The team, which included biologists Daniel Sol of the Autonomous University of Barcelona and Louis Lefebvre of McGill University in Montreal, analyzed a previously compiled global database that documents the results of 645 attempts by humans to introduce 195 bird species to entirely new locations, such as islands or different continents. The measure of success was whether the birds could establish a new, self-sustaining population.

Out of the 645 attempts, 243 succeeded. Among those species, success rate correlated with relative brain size, the team reports in the March 14 online early edition of the Proceedings of the National Academy of Sciences. The bigger the brain, the more successful the birds were at overcoming the challenges of a new environment, such as finding new food resources or avoiding predators. And birds that showed a greater ability to innovate by finding new foods or developing new feeding techniques--a standard indication of cognitive capacity--were more successful at establishing new colonies.

"This is an important finding, and an exciting marriage between ecology and psychology," comments behavioral biologist Simon Reader of the University of Utrecht in the Netherlands. "It provides clues for the factors that may have favored the evolution of enlarged brains." Nevertheless, Reader cautions, it is still an open question whether the ability to innovate is solely responsible for the birds' success, or whether some other cognitive talents--such as the ability to make changes in their social behavior--may also be correlated with increased brain size.

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