Depending on whether you're a dog person or cat person, there's a good chance you fall firmly on one side of this question: Do dogs rule or are cats masters of the mental domain?
New research led by Vanderbilt University neuroscientist Suzana Herculano-Houzel aimed to answer the "who's smarter" question. Not only did her research team look at the brain size of a number of animals, but they also counted the number of neurons — the brain cells responsible for thinking, planning and complex behavior — which is a much more definitive measure of intelligence.
"Brains are made of neurons, the basic information unit. Whoever has the most neurons would have the most information processing capability," Herculano-Houzel tells MNN. "If the cerebral cortex has more neurons, you would expect whoever has the most would have the most cognitive capabilities."
In their research, the scientists found that dogs have twice as many neurons in their cerebral cortexes as cats. Sorry, feline fans.
The explanation for their intelligence likely comes from their ancestry, says Herculano-Houzel.
"Dogs have been selected from wolves. They have wolf-like ancestors and humans have been practicing artificial selection on those wolf-like derived animals. The ancestor was a large carnivore with a large brain that must have had a large number of neurons," she says. "The ancestor of the cat was likely a cat-sized animal, and it might be as simple as that."
The new study was published in the journal Frontiers in Neuroanatomy. Herculano-Houzel explains the study here:
Looking at other animals
The researchers didn't limit their study to just pets. They looked at the neurons and brains of an array of carnivorans, which are an order of mammals that includes 280 species. For the study, in addition to dogs and cats, the researchers looked at ferrets, mongooses, raccoons, hyenas, lions and brown bears.
They expected to find that the predators would likely be smarter than their prey.
"Large meat-eating carnivorans have to hunt. One of our early expectations was that it certainly has to be hard to hunt because it's not just outrunning your prey, you also have to outsmart your prey," Herculano-Houzel says.
But that's not what they found. The largest carnivorans, like the lion and brown bear, were actually missing neurons — to the point that the large bear only has as many neurons in its cerebral cortex as the cat.
"They must not be able to get the energy it would require to run their large body and a large number of neurons in the cortex," Herculano-Houzel says. "It costs so much energy to chase prey with very long legs. Your food runs away too fast. It made me think of large carnivorans in a completely different way."
Not the end of the argument
But let's circle back to the cat-dog debate. Although dogs appear smarter than cats with this study, not all dogs are necessarily as bright as the brightest one.
"The expectation was it might be the case that among dogs, they might have a similar number of neurons because all dogs are one species," Herculano-Houzel says, but that wasn't what they found.
A golden retriever has 50 percent more neurons than a small dog, which prompted the team to want to study a wide range of breed brains in the future.
For her part, Herculano-Houzel admits she's a dog person and insists no bias, but she's fascinated by all matter of brains. She is the author of "The Human Advantage: A New Understanding of How Our Brain Became Remarkable."
For cat lovers, Herculano-Houzel points out that this is by no means the final word on animal braininess.
To help illustrate the difference between dog and cat cognitive abilities, she points out that researchers know humans have about twice as many neurons in the cerebral cortex as gorillas.
"Between cats and dogs, you could expect a similar type of difference where dogs have twice as many neurons as cats," she says. That means they should be better at planning, problem solving, making good decisions based on past experiences.
"But that says nothing about what cats and dogs are actually able to do," she says. "And that should have nothing to do with how much we love these animals."