In 335 B.C., Aristotle wrote, “Of all the animals, man has the brain largest in proportion to his size.” It has been assumed for a long time that brain size is directly related to levels of intelligence; but the evolutionary process by which certain species evolved larger brains – encephalization – is still not well understood.
Dr. Humberto Gutierrez of the School of Life Sciences at the University of Lincoln chose to examine the question of encephalization a little further, and found a link between increased brain size and the expansion of gene families that are related to specific biological functions.
In a study published recently, Gutierrez examined the genomes – or the entirety of all hereditary information about an organism – of 39 different species of mammals, hoping to understand exactly how encephalization occurs in mammals. Gutierrez and his team concentrated on the size of gene families across these 39 species. “We found that brain size variations are associated with changes in gene number in a large proportion of families of closely related genes,” Dr. Gutierrez said in a news release. “These gene families are preferentially involved in cell communication and cell movement as well as immune functions and are prominently expressed in the human brain. Our results suggest that changes in gene family size may have contributed to the evolution of larger brains in mammals.” Mammals in general tend to have larger brains compared to their body size, as measured by the encephalization quotient.
“The brain is an extremely expensive organ consuming a large amount of energy in proportion to its volume; so large brains place severe metabolic demands on animals,” Dr. Gutierrez said in the news release. “Larger brains also demand higher parental investment. For example, humans require many years of nurturing and care before their brains are fully matured.” Because larger brains require increased physiological demands, Gutierrez believes that variations in the size of gene families associated with encephalization ultimately were a form of evolutionary support for those increased demands.