Human Brain vs Dog Brain: How Many Neurons Does Each Have?

In the human brain vs dog brain comparison, a human has about 86 billion neurons and a dog about 1.8 to 2.6 billion. In the cerebral cortex the gap is roughly 26 to 37 times: about 16 billion neurons against 429 and 623 million in two dogs. One cat had 250 million. Size misleads: the human brain weighs 1,508 g, the dog and cat brains 34.8 to 114.5 g.

Below: the numbers side by side, for dog brain vs human brain and cat brain vs human brain. Then why brain size is a poor guide, what we could not find for sheep, and why a neuron count is not an IQ.

Human brain vs dog brain: how do the neuron counts compare?

A dog brain has far fewer neurons than a human brain, but more than a cat's. The best direct comparison comes from Jardim-Messeder and colleagues. In 2017 they counted neurons in eight carnivoran species, among them the dog, cat, lion and brown bear. Their paper in Frontiers in Neuroanatomy is titled "Dogs have the most neurons, though not the largest brain". The human figures are the adult male average reported by Herculano-Houzel (Frontiers in Human Neuroscience, 2009), who reviewed the counts of Azevedo and colleagues.

• Human, adult male average: brain 1,508 g; 86 billion neurons in the whole brain; about 16 billion neurons in the cerebral cortex (cortex mass 1,233 g)
• Dog, golden retriever: brain 114.5 g; 2.6 billion neurons in the whole brain; 623 million in the cortex (the paper also prints 627 million)
• Dog, smaller dog of unspecified breed: brain 58.4 g; 1.8 billion neurons; 429 million in the cortex
• Cat, one animal: brain 34.8 g; 1.2 billion neurons; 250 million in the cortex

Compare one measure at a time. The human brain is 13 to 26 times heavier than the two dog brains, but it has 33 to 48 times their neurons. The gap in the cerebral cortex is wider, 26 to 37 times. Those ratios are our arithmetic on the figures above.

Size of dog brain vs human brain: is a dog's brain smaller?

Yes, but the size of dog brain vs human brain tells you little about neurons. In a human vs dog brain comparison by weight the gap is 13 to 26 times, and by neurons it is 33 to 48 times. Herculano-Houzel wrote in 2009 that brain size "can no longer be considered a proxy for the number of neurons", because different animal groups pack neurons by different rules. The 2017 paper makes the same point inside one order of mammals.

Their abstract says the golden retriever had more cortical neurons than the striped hyena, the African lion and the brown bear. Those animals have cortices up to three times larger. The team links this to energy cost: neurons are expensive to run, and large carnivorans appear to trade body size against the number of cortical neurons they can afford.

Dogs may escape that squeeze. The authors note that dogs have adapted to a starch-rich diet shared with humans, which might protect them from the limits that larger carnivorans face. That is their suggestion, not a measured result.

How does a cat brain compare with a human brain?

A cat brain holds about 1.2 billion neurons against a human's 86 billion, so the human brain has about 72 times as many. In the cortex the cat's 250 million compares with the human's 16 billion, a 64-fold gap. Our guide to cat IQ explains why no IQ number exists for cats either.

Between dog and cat, the study found the dog ahead. The retriever's cortex had about 2.5 times the cat's neurons and the smaller dog's about 1.7 times. The paper also reports that a raccoon, with a cat-sized cortex of about 24 g, had 438 million cortical neurons against the cat's 250 million. The authors say this gives the raccoon a neuron density comparable to that of primates.

One caution matters here. The sample is small: the paper analysed one brain hemisphere from one or two animals per species, which means two dogs and one cat. Treat the dog and cat counts as the best available estimates, not as species averages. Our dog IQ page and the review of smartest dog breeds show how animal comparisons depend on the task chosen.

What about sheep brain vs human brain?

For a sheep brain vs human brain comparison, we found no published neuron count for the sheep in the sources we read, so we give none. The closest study of hoofed animals, by Kazu and colleagues (Frontiers in Neuroanatomy, 2014), counted the pig, springbok, blesbok, greater kudu and giraffe, not the sheep.

If you are comparing the two for a class dissection, the structures are the point, and a neuroanatomy textbook is the right source. A neuron count cannot be read from the size of a specimen, as the dog and bear results above show.

Does having more neurons mean being smarter?

Not in any way that can be scored, so a human brain vs dog brain list is not an intelligence ranking. Herculano-Houzel argues that cognitive ability should be judged by the absolute number of neurons, not body size. That is a hypothesis about animal brains, not a test result.

Nobody has given an IQ test to a dog. An IQ is a position on a human bell curve with an average of 100 and a standard deviation of 15, so it only applies to people. See the IQ bell curve for how that scale works.

Even among people, bigger is only slightly better. A synthesis of 88 imaging studies puts the link between brain volume and IQ at about 0.24, as we explain in our article on brain size and IQ. Our look at gifted brain scans shows what a 2021 imaging study measured in children with IQ scores above 145. Our ranking of the smartest animals shows why animal lists depend on the task. For a cat, see also the smartest breed of cat.

How should you read brain-comparison claims?

• Ask how many animals were counted: two dogs and one cat is a small sample
• Ask which part: whole-brain neurons and cortical neurons give different ratios
• Distrust size as a shortcut: a ten times larger cortex can hold the same number of neurons
• Do not turn a neuron count into an IQ: animals have no norm group
• Check the species: a result for a golden retriever is not a result for every dog

You can test one human skill, short-term memory, in our memory game. It scores memory, not IQ. For a measure that does have a norm group, take the IQ test.

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