Overall Brain Size Predicts Intelligence Level

A big brain means more intelligence.

Even without adjusting the brain size to the body size, this remains valid, as found by a mix team from Grand Valley State University and the Anthropological Institute and Museum at the University of Zürich, Switzerland.

"It's long been known that species with larger body sizes generally have larger brains," said first author Robert Deaner, assistant professor of psychology at Grand Valley.

"Scientists have generally assumed that this pattern occurs because larger animals require larger nervous systems to coordinate their larger bodies. But our results suggest a simpler reason: larger species are typically smarter."

These discoveries imply a re-evaluation of many previous studies that have linked brain size to intelligence across different species, including ancestral hominids, related to their body size.

In July 2006, the same team detected that some primate species always outperform others in many cognitive tests, in other words some species are more intelligent.
This intelligence offers an animal the ability to cope with new and unpredictable situations.

Domain-general cognitive ability opposes domain-specific skills for the suited specific environment challenges, like a bird remembering where it hid food items.
The new approach assessed how well eight different brain sizes forecast the domain-general cognitive ability.

The team found that overall brain size and overall neocortex (the "thinking part" of the brain) size were tightly linked to intelligence, but adjustments to the body size did not. In this case, larger animals are always more intelligent than smaller ones.

"Larger animals may be better able to control aspects of their environment and therefore have more to gain from being more intelligent. But perhaps more important is that larger animals tend to live longer, and can therefore benefit longer from being flexible and adaptable, and perhaps may also need it more because the environment is more likely to change during their lifetime,"said co-author Dr. Carel van Schaik, director of the Anthropological Institute and Museum at the University of Zurich.

Deaner noted, "We believe that most of the relationship between brain size and body size is due to larger animals being smarter, but it's certainly possible-even likely-that some part of the relationship is due to larger animals needing to maintain greater neural traffic. Our point is that completely controlling for body size is almost certainly a mistake." said Deaner.

"The human brain imaging data indicate that some correction for 'neural traffic maintenance' is probably needed. If it wasn't needed, then we would be stuck with some real puzzles, such as the fact that there are no consistent sex differences in IQ, yet men generally have larger brains. And, of course, elephants and whales possess larger brains than we do, yet it's hard for us to imagine that they are smarter than we are." added Deaner.