Bad news for cat lovers. Your pet is not haughty, enigmatic and given to philosophical pondering. Your pet is just dumb.
Dogs on the other hand are quite smart – at least compared to cats. And brown bears, as it turns out.
These findings – which derives from firm anatomical data – arose from research led by biological scientist Suzana Herculano-Houzel of Vanderbilt University in Nashville, US.
Herculano-Houzel and colleagues set out to test the hypothesis that carnivores should have more developed brains than the herbivores on which they prey. The theory stems from the assumption that hunting is more cognitively demanding than plant-eating, so therefore evolutionary pressure should have favoured a more adaptable brain.
Surprisingly, the researchers found that this idea – almost a touchstone of evolutionary theory – didn’t hold up.
To make their findings, the scientists opted to count the neurons in the cerebral cortex of eight carnivore species: cat, dog, ferret, raccoon, hyena, lion, brown bear and mongoose. Cortical neurons are associated with higher brain functions, so their number and density can be used as a proxy for intelligence.
Cats, the study found, have about 250 million of them. Dogs have more than double that: 530 million.
Ergo, dogs are smarter than cats.
Humans, by the way, have 16 billion. That’s why we own pets, and not the other way around.
The more significant conclusion arising from the study, however, was that small to medium size carnivores have about the same number of neurons as herbivores. This suggests that evolutionary pressure on planet-eaters to develop ways of avoiding predators is roughly the same as the pressure on predators to catch them.
The findings for large carnivores were even more surprising. Lions? Brown bears? Dumb as a box full of trumpets, both of them.
Herculano-Houzel’s team found the ratio of neurons to brain size in the big hunters was lower than that of their prey. A golden retriever has more neurons than a lion, despite being only a third of the size. And brown bears have the same number of neurons as cats, even those their brains are 10 times bigger.
The results, say the researchers, can be explained in terms of evolutionary trade-offs. Brains are energy-intensive organs and carnivorous diets in the wild are sporadic. The energy demands of maintaining a large body mass – necessary for the hunting strategies of large carnivores – is played off against the need to be smart enough to use it.
“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.
Cats and dogs, of course, in most cases don’t have to use their brains or their bodies to secure meat. All they have to do is wait for their owners to open a can. However, that doesn’t imply that cats find anything interesting to do with their unused brain capacity.
Cats are stupid, it seems, and always will be.
“I’m 100 percent a dog person,” says Herculano-Houzel, “but, with that disclaimer, our findings mean to me that dogs have the biological capability of doing much more complex and flexible things with their lives than cats can.
“At the least, we now have some biology that people can factor into their discussions about who’s smarter, cats or dogs.”
Andrew Masterson is a former editor of Cosmos.
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