Photo: Mostphoto
Photo: Mostphoto

The results suggest that there is a positive genetic link between brain size and several male specific sexual characteristics such as color pattern, size of genitals, etc. It may be that the same genes encode both brain size and sexual characteristics. Because the more colorful males with larger tails are more attractive among females the results also suggest that attractiveness and smartness go together.

The relationship between brain size and sexual characteristics

The study has examined the relationship between brain size and primary and secondary male sexual characteristics. Existing theory suggests that brain size and male sexual characteristics, both highly costly traits, should be negatively correlated because an individual is not expected to have enough resources to invest the maximum in all of its properties.

The researchers tested this hypothesis in guppies where they had grown four generations of fish selected for relative brain size. They generated groups of guppies with about 14 percent difference in brain size, but no difference in body size, between the selection lines selected for large and small brains.

Evolution towards smarter individual may lead to more attractice individuals

“When we compared the sexual characteristics color patterns, tail size, condition and genital size, we found that males with larger brains were more colorful, had larger tails, larger gonopodium (the male sex organs in guppies), and even better condition when they were kept in groups”, says Niclas Kolm at the Department of Zoology, Stockholm University.

The results indicate that the evolution of attractiveness, brain size and intelligence may be related in vertebrates. Evolution towards smarter individuals could thus also lead to the evolution towards more attractive individuals.