The standing belief when it comes to brainpower is that humans use exceptionally large amounts of energy to power the brain compared to other animals. A new study finds that humans may share this quality with other animals as well.
The Human Brain
Other animal species such as whales and dolphins have big and complex brains and are often seen as intelligent creatures that are capable of completing more complex tasks. Still, there is a long-standing belief that the amount of energy humans use to power their brains is quite unique to the animal kingdom. That is, humans use more energy for brainpower.
In fact, although the human brain makes up for a fairly small percentage of the human body weight at just 2 percent, it accounts for a quarter of the body's energy usage.
A new study conducted by researchers from Duke University found that although humans do in fact use a large amount of energy for brainpower, this may not be as unique to the species as previously thought.
Not As Exceptional As We Think
To see just how humans' energy uptake for brainpower compares to other animals, researchers measured the cross-sectional area of the bony canals of a total of 22 animal species including humans, mice, monkeys, lemurs, and treeshrews.
Not surprisingly, researchers found that humans indeed allot more energy for brainpower compared to other animals such as chimpanzees and orangutans. In fact, the resting metabolic rate of the human brain uses up to almost three times more energy than chimpanzee brain and up to five times more energy than mice, squirrel, and rabbit brains.
However, other smaller animals such as the pen-tailed treeshrew and the pygmy marmoset, the world's smallest monkey, devote similar amounts of energy to brainpower as we do.
"The metabolic cost of a structure like the brain is mainly dependent on how big it is, and many animals have bigger brain-to-body mass ratios than humans," said Doug M. Boyer of Duke University.
In previous studies, researchers calculate energy utilization for the brain by measuring neurons. But because researchers of the current study measured bone and not soft tissue, it's now entirely possible to measure the brain energy demands of now-extinct animals and even early humans.
"We don't have a uniquely expensive brain," said Boyer, as the results of their study suggest that the development of more "expensive" brains may have developed not with humans but millions of years earlier when the earliest primates split from the evolutionary family tree.
The question now is whether the brains evolved first, giving way to better mental abilities, or if the cognitive challenges of evolution led to the utilization of more energy for the brain and its development.
The study is published in the Journal of Human Evolution.