Brain size puzzle solved as humans outpace evolutionary trend

Larger animals do not have proportionally larger brains – with humans contradicting this trend – a study published in Nature Ecology and Evolution has discovered.

Researchers at the University of Reading and Durham University collected a large dataset of brain and body sizes from around 1,500 species to clarify centuries-old debates about the evolution of brain size.

Larger brains relative to body size are associated with intelligence, sociability, and behavioral complexity—with humans having evolved unusually large brains. New research reveals that larger animals do not have proportionally larger brains, challenging long-held beliefs about brain evolution.

Professor Chris Venditti, lead author of the study from the University of Reading, said: “For more than a century, scientists have assumed that this relationship was linear – meaning that brain size becomes proportionally larger as to be an animal. Now we know this is not true, the relationship between brain size and body size is a curve, basically meaning that very large animals have smaller brains than expected.

Professor Rob Barton, co-author of the study from Durham University, said: “Our results help to unravel the strange complexity in the brain-body mass relationship. Our model has a simplicity which means that previously elaborated explanations are no longer valid. necessary—the relative size of the brain can be studied using a single basic model.”

Beyond the ordinary

The research reveals a simple correlation between brain and body size in all mammals, which allowed researchers to identify rule breakers – species that defy the norm.

Among these differences is our own species, Homo sapiens, which has evolved more than 20 times faster than all other mammalian species, resulting in the massive brain that characterizes humanity today. But humans aren’t the only species bucking this trend.

All groups of mammals demonstrated rapid bursts of change—both toward smaller and larger brain sizes. For example, bats reduced their brain size very quickly when they first arose, but then showed very slow rates of change in relative brain size, suggesting that there may be evolutionary constraints related to the demands of flight.

There are three groups of animals that showed the most rapid change in brain size: primates, rodents, and carnivores. In these three groups, there is a tendency for relative brain size to increase over time (the “Marsh-Lartet rule”). This is not a universal trend for all mammals, as previously believed.

Dr. Joanna Baker, co-author of the study also from the University of Reading, said: “Our results reveal a mystery. In larger animals, there is something that prevents the brain from getting too big. If this is because the brain is bigger than a Whether certain proportions are simply too costly to maintain remains to be seen.