Comparisons of different animals have shown that larger brains provide greater intelligence, but they also guzzle more energy and have other consequences. Now scientists have observed the effects of varying brain size within a single species: guppies. The work is in Current Biology. [Alexander Kotrschal et al., Artificial Selection on Relative Brain Size in the Guppy Reveals Costs and Benefits of Evolving a Larger Brain]

Swedish researchers bred two different lines of guppies, selecting one for larger brains and one for smaller. The fish quickly modified until brains were nine percent larger in the big-brained line than in the other.

Not surprisingly, when 48 guppies were given learning tests, large-brained female fish outperformed small-brained females. However, males from both lines scored about the same, possibly because the female guppies' visual system was more suited to the type of intelligence test used.

But big brains also had a downside—the brainier fish had smaller guts, by 20 percent for males and 8 percent for females. Plus, the large-brained guppies produced 19 percent fewer offspring. In order to provide energy to their bigger brains, the egghead fish made sacrifices that may be evolutionary disadvantages. It may indeed be possible to be too smart for your own good.

—Sophie Bushwick

[The above text is a transcript of this podcast.]