Brain-to-bodymass ratio correlates with reasoning needed to retrieve rewards
Brains are expensive. Aside from growing the tissue, and then some skull to keep that tissue safe, brains demand a relatively high number of calories each day to do their job. Humans, with relatively large brains, give up as much as 20 percent of our resting metabolic rate to power these organs each day, which breaks down to 10.8 calories an hour or so. Considering ourselves to be pretty smart, we generally assume we’re getting a good return on this caloric investment. Applying these ideas to the animal kingdom has been a bit less clear cut, but a new study suggests that relatively larger noggins in many animals makes them more successful thinkers as well.
How much mind matters
While our brain is bigger than a that in a rat or a dog, it’s not the raw weight that scientists are interested in in these studies. If that were the measure of cognition, even a human would be dauntingly stupid compared to a sperm whale’s 17.5 pound brain. Instead, researchers focus on the size of the brain relative to the rest of the animal’s body, which has long been offered as the best physical metric to gauge intelligence. For example, a 150 pound chimpanzee’s 0.8 pound brain makes up a larger portion of the animal’s total mass than a 400 pound gorilla’s 0.9 pound brain. This hypothesis would then predict that chimps are more cognitively capable than mountain gorillas, even with the smaller heads.
To compare just two species risks anecdotal evidence to creep in, as one animal might just be better a particular kind of test. To try to look for larger trends in brain sizes, 140 animals across 39 different species were given the same test at various zoos. To limit the number of variables in play, all the participants were mammalian carnivores, including polar bears, tigers, binturongs and wolverines. Each animal had 30 minutes to get an appropriate snack out of a closed box, which basically required moving a sliding bolt latch, then opening a door.
Sorting the successes
The results did show some trends, but they weren’t immediately obvious. Bears had the most success, opening the box 70 percent of the time and beating the overall average of a 35 percent completion rate. They also stood out against the fact that overall, larger animals did worse than smaller ones. But bucking that trend, the relatively small meerkats and mongooses failed more than any species, never managing to open the snack-box once. Sociability of each species was also considered, but no clear trends emerged favoring social animals over loners. The one pattern that did hold was that the relative brain-size of each creature did correlate with their problem-solving abilities, adding support to the brain-size hypothesis.
Source: Study shows animals with larger brains are best problem solvers, Scienmag
