It’s long been debated which is smarter – dogs or cats? Those in the dog camp claim that the ability to be trained makes man’s best friend the brainiest, while fans of felines argue that a cat’s nonchalance, independence, and high standards make it far superior. Cats were once worshipped as gods, after all.
However, science seems to have brought new evidence to the debate, something that will bring smug satisfaction to every “dog person”. It turns out that dogs have many more neurons in the cerebral cortex of their brains than cats. These special cells are associated with various signs of intelligence like thinking, planning, and complex behavior.
Published in the journal Frontiers in Neuroanatomy, the study didn’t just focus on our favorite pets. The international team of scientists looked at the brains of various carnivore species too. Interestingly, they found that only the smaller species – dogs and smaller – have higher densities of cortical neurons. Striped hyenas have fewer than dogs, for example, and brown bears have the same number as cats.
Meanwhile, raccoons, despite having small, cat-sized brains, have as many neurons as dogs, making them “comparable to primates in neuronal density”, and therefore rather smart. No wonder they can solve puzzles and are famed for being cunning thieves.
What’s more, domestication didn’t seem to have any effect on neuronal composition in the brains of the carnivores tested in the study.
"I believe the absolute number of neurons an animal has, especially in the cerebral cortex, determines the richness of their internal mental state and their ability to predict what is about to happen in their environment based on past experience," said study author Suzana Herculano-Houzel of Vanderbilt University in a statement.
The team found that dogs have around 530 million cortical neurons in their brains, while cats have just 250 million. For scale, humans have 16 billion. But before you get too smug about how smart people are, long-finned pilot whales have 37 billion. In fact, according to a 2016 article in Scientific American Mind, this “plays havoc with the notion that humans have more nerve cells where it counts than any other species on the planet”.
The researchers in this latest study chose to analyze carnivores due to the wide range of sizes it incorporates – from the powerful polar bear to the little least weasel – and the fact that it includes both wild and domestic animals. The team looked at the brains of eight species: ferrets, mongooses, raccoons, cats, dogs, hyenas, lions, and brown bears.
Before the study, they predicted that these creatures would have more cortical neurons than the herbivores they hunt. However, to their surprise, they found that the neurons-to-brain size ratio in small- and medium-sized carnivores was actually the same as in herbivores, and that in large carnivores like bears, it was lower. Although the team's sample size was small, it appears that prey animals require more intelligence to escape being hunted than we tend to give them credit for.
The lower numbers of cortical neurons in large carnivores is likely due to the energy that the brain requires – energy-wise, the brain is our most expensive organ.
"Meat eating is largely considered a problem-solver in terms of energy, but, in retrospect, it is clear that carnivory must impose a delicate balance between how much brain and body a species can afford," said Herculano-Houzel in the statement.
So, dogs are smarter than cats, but cortical neuron density is not the be-all and end-all of intelligence. “There are multiple ways that nature has found of putting brains together – and we're trying to figure out what difference that makes," explained Herculano-Herzel.