Evolution Is A Matter Of Brawn Vs Brain
October 16, 2012

Brawn Vs Brain In Evolutionary Selection

April Flowers for redOrbit.com - Your Universe Online

Brain size relevant to body size has been the most common measurement of intelligence in animals, but it may not be as dependent on evolutionary selection of the brain as was previously thought. This is according to a new study published this week in the Proceedings of the National Academy of Sciences.

A generation of scientists has used brain size relative to body size to predict an animal's intelligence. An example is the human brain. It is not the largest in the animal kingdom in either volume or mass, but in relation to our body mass, it is exceptionally large.

A team of scientists from University College London, the University of Konstanz, and the Max Planck Institute of Ornithology has found that in different animals, the two traits of brain size and body size are driven by different evolutionary mechanisms.

Most significantly, the team has found that the most deciding factor in determining relative brain size is often evolutionary pressure on body size, and not brain size. The evolutionary history of bats, for example, suggests that they decreased body size much faster than they decreased brain size, leading to an increase in relative brain size. Small bats maintained the brainpower to handle foraging in cluttered environments while still developing improved flying maneuverability, showing that relative brain size cannot be used as evidence of selection for intelligence unequivocally.

Dr Jeroen Smaers of the UCL Anthropology and UCL Genetics, Evolution & Environment departments said, "When using brain size relative to body size as a measure of intelligence, the assumption has always been that this measure is primarily driven by changes in brain size. It now appears that the relationship between changes in brain and body size in animals is more complex than has long been assumed. Changes in body size often occur independently of changes in brain size and vice versa. Moreover, the nature of these independent changes in brain and body size, are different in different groups of animals."

Scientists at UCL gathered brain and body mass data for hundreds of modern and extinct species of bats, carnivorans and primates. They charted the change in brain and body mass over time for each species, showing that across millions of years, most animals increased body size faster than brain size with the exception of bats.

Decreases in brain size slightly outpaced those for body size in primates, while carnivoran evolution took an even different tack. Changes in carnivorans were generally more strongly associated with body size rather than selection on brain size and cognition.

The team believes that the predominant theory of relative brain size as a direct consequence of selection on intelligence masks the more significant influence of selection on body size.