Ever since humanity split into dog and cat people, we’ve been arguing over which one of our beloved companions is a smarter species.
This latest study mightn’t be the last word on the matter, but for those who think more neurons means more intelligence, it looks as if dogs stand out among carnivores for having a remarkably dense cerebral cortex.
An international team of researchers analysed the wrinkled outer layers of the brains of a variety of carnivorous animals – including dogs and cats – to determine whether the demands of hunting prey mean a higher count of cortical neurons, adding brain power where it counts.
On one hand, it would seem like a no-brainer – hunting prey requires special behaviours that you’d imagine would be neurologically taxing.
But those extra brain cells come at a cost, and not every hunt results in an energy-boosting kill.
To compare the brains of different animal species, it’s not enough to just weigh their grey matter, because we have to take into account their relative body-and-brain sizes.
Even looking at brain size as a ratio – something called an encephalisation quotient – can fail to provide the big picture when it comes to the details of brain anatomy and intelligence.
Counting the cells, on the other hand, is thought to provide a better match for determining relative amounts of processing power.
“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,” says neuroscientist Suzana Herculano-Houzel from Vanderbilt University in the US.
Past studies have compared the ‘neural packing density’ in the brains of our favourite carnivorous pets, estimating that cats have about 300 million neurons, roughly doubling the 160 million of dogs.
But it seems we might have been a little hasty handing the trophy to cats.
The team looked at eight different meat-eating animals, analysing one or two representative specimens of ferret, mongoose, raccoon, cat, dog, hyena, lion, and brown bear.
Based on their results, dogs have closer to 530 million neurons, compared to the 250 million of cats.
What’s more, dogs had the most neurons of any carnivore, even though they didn’t have the largest brains.
The researchers had hypothesised carnivore brains should have more neurons in their cerebral cortex than their prey. It turns out, there wasn’t much of a difference at all.
The ratio of neurons to brain size in most carnivores was roughly equivalent to that of herbivores, suggesting the hunted needed about the same level of brain power to escape as the hunters needed to catch them.
If anything, the pattern reversed for larger carnivores – bigger meat eaters, such as brown bears, had comparatively fewer neurons for their size. In fact, while ten times larger than most cats, the two animals shared the same number of cortical neurons.
“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,” says Herculano-Houzel.
Being bigger might help when it comes to catching food, but that doesn’t translate into needing to be smarter. Thinking is hard work that doesn’t always help pay for itself.
So is it time to give dogs their due?
“I’m 100 percent a dog person,” Herculano-Houzel confesses, “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.”
Capability might not necessarily be realised as intelligence, of course. Cats are notoriously harder to study – not because they’re stupid, but because frankly they just don’t care for our ‘science’.
And if you’re a dog person cracking out the champagne to celebrate anyway, here’s one more fun fact.
The real oddball carnivore is the racoon – even though it’s close to cats in terms of size, it actually has a similar number of neurons to dogs. Considering raccoons can smash intelligence tests, we’re not surprised.
This research was published in Frontiers in Neuroanatomy.
A version of this article was first published in November 2017.