Dogs are no match for humans in terms of this particular measurement, however. A person has about 16 billion cortical neurons while a dog has approximately half a billion. In other words, we have around 32 times as many of these information-processing units.
Prior research determined that a honeybee has approximately 1/1000 as many neurons as a dog cortex does.
“Yet honeybees certainly can do pretty complex things, like navigate to a particular spot and remember that location,” Herculano-Houzel noted. “However, they do that for a very short time. I have a suspicion that having more neurons is a requirement for living long, complex lives.”
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This complexity could extend to the animal's thoughts as well. Herculano-Houzel, lead author Débora Alvarenga and their team are therefore now considering the possibility that dogs are deeper thinkers than most of us might imagine.
The neuronal composition of carnivore brains is not affected by domestication either, according to the scientists. Genetics then appears to be a key determinant of intelligence.
Genetics could help to explain why dogs have so many cortical neurons. Dogs — from toy poodles to Great Danes — are all thought to have descended from wolves, which are larger animals than the ancestors of today's cats. Despite the varying sizes and shapes of dogs, they can cross-breed and are thought to possess similar levels of intelligence.
Another major factor underlying braininess appears to be energy availability.
“We humans could not afford all the neurons that we have if we still ate raw foods like other primates,” Herculano-Houzel said.