Bigger brains can make animals, well, brainier, but that boost in brain size and ability comes at a price. That's according to new evidence reported on January 3rd in Current Biology, a Cell Press publication, in which researchers artificially selected guppies for large and small brain sizes.
The findings lend support to the notion that bigger brains and increased cognitive ability do go together, a topic that has been a matter of considerable debate in recent years, said Niclas Kolm of Uppsala University in Sweden. They also represent some of the first convincing evidence that large brains are expensive, evolutionarily speaking.
"We provide the first experimental evidence that evolving a larger brain really is costly in terms of both gut investment and, more importantly, reproductive output," Kolm said.
Together, the findings strongly support the idea that relative brain sizes among species are shaped through a balance between selection for increased cognitive ability and the costs of a big brain.
The results in guppies have important implications for us humans. After all, one of the most distinctive features of the human brain is its large size relative to the rest of the body.
"The human brain only makes up 2 percent of our total body mass but stands for 20 percent of our total energy demand," Kolm said. "It is a remarkably costly organ energetically."
But support for the so-called "expensive-tissue hypothesis"that there is a trade-off between the brain and the energy demands of other organs and reproductioncame only from comparative studies among species and were correlative in nature.
In the new study, Kolm's team took a different, within-species approach. They selected live-bearing guppies for large and small brains relative to the size of their bodies. Under that strong selection pressure, they found that brain size could evolve "remarkably quickly."
After selection, large-br
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