Summary: Researchers studied brain and body sizes from 1,500 species, finding that larger animals do not have proportionally larger brains, challenging long-held beliefs. The study reveals that the brain-body size relationship is curvilinear, not linear.
This finding helps explain why humans and other species deviate from the norm in the evolution of brain size. The findings provide a simpler model for studying brain evolution in mammals.
Key facts:
- Curved relationship: Brain size increases at a slower rate than body size in larger animals.
- Human exception: Humans have evolved significantly larger brains relative to body size.
- Evolutionary constraints: Some species, such as bats, show unique variations in brain size due to evolutionary pressures.
Source: University of Reading
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, published today, 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 be an animal. We now know that this is not true.
“The relationship between brain 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 that means previously elaborate explanations are no longer necessary – the relative size of the brain can be studied using a single underlying model.”
Beyond the ordinary
The research reveals a simple correlation between brain and body size across mammals, which allowed researchers to identify rule breakers – species that defy the norm.
Among these differences includes our species, homo sapiens, which 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. Whether this is because large brains beyond a certain size are simply too expensive to maintain remains to be seen.
“But as we also observe similar bending in birds, the pattern appears to be a general phenomenon – what causes this ‘curious ceiling’ applies to animals with very different biology.”
About this neuroscience and evolution research news
Author: Ollie Sirrell
Source: University of Reading
Contact: Ollie Sirrell – University of Reading
Image: Image is credited to Neuroscience News
Original research: The findings will be published in Nature Ecology and Evolution