No direct correlation between body mass and brain size, finds new study

PTI, Jul 10, 2024, 11:49 AM IST

Representative image (Source: Pexels)

New Delhi: A bigger body may not always necessarily mean a bigger brain, claimed a research team that has found a disproportional relationship between the two.

For more than a century, scientists have thought that the larger an animal is, the brain is proportionally bigger – a “linear” or a straight-line relationship, according to the study’s authors.

“We now know this is not true. The relationship between brain and body size is a curve, essentially meaning very large animals have smaller brains than expected,” said lead author Chris Venditti from the University of Reading, UK.

The study, published in the journal Nature Ecology and Evolution, revealed a “simple association” between body size and brain across all mammals, which also allowed the researchers to identify species departing from the norm.

Evolving over 20 times faster than other mammals, humans are known to have massive brains compared to their body size and considered outliers in this regard. Bigger brains compared to the body are related with intelligence, being social and complex behaviours.

However, in this study, the authors identified other species also bucking the trend — primates, rodents, and carnivores.

In these three groups, there is a tendency for the brain size (relative to the body) to increase with time, according to the ‘Marsh-Lartet’ rule. But this is not a trend universal across all mammals, as previously believed, the researchers said.

Even as all mammals have shown rapid bursts of change, both towards smaller and bigger brains, “in the largest animals, there is something preventing brains from getting too big,” according to study co-author Joanna Baker from the University of Reading.

“Whether this is because big brains beyond a certain size are simply too costly to maintain remains to be seen,” said Baker.

“But as we also observe similar curvature in birds, the pattern seems to be a general phenomenon — what causes this ‘curious ceiling’ applies to animals with very different biology,” said Baker.

For instance, bats very rapidly reduced their brain size when they first arose, but then changes to their brain sizes slowed down, suggesting there may be limits as to how big their brains could evolve because of demands of flight, the research team said.