BRS: PDF Wouter van der Bijl "Evolving a larger brain: Using artificial selection to measure benefits, costs and constraints"

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Brain size is one of the most studied quantitative traits in animals. It has been the subject of extensive comparative analyses, a plethora of adaptive hypotheses, and substantial controversy about its role in humans. Experimental evidence on the costs and benefits of brain size, however, is surprisingly rare. I will present results from an artificial selection experiment, where guppies were selected to have small and large brains, resulting in a 15% difference in relative brain size. Using these selection lines, we are able to finally test many claims about the evolution of vertebrate brains for which only correlative evidence existed before. Selection on overall brain size affected all the regions of the brain, and the numbers of neurons therein. Large-brained fish performed better on several cognitive tests, as predicted. Apart from differences in standard cognitive assays, brain size also had remarkable effects on performance in ecologically relevant tasks, including predator avoidance and survival, mate choice and social competence. These behavioral benefits of large brains come at a physiological cost, including smaller guts, a reduced immune response and a shorter life span. Based on these results, I evaluate the current state of the field of brain size research, and identify promising avenues for future research.