Dogs with larger brains outperform smaller dogs in some intelligence tests, according to new research published in the journal Animal Cognition.
The study found that bigger dogs have better short-term memory and self-control than smaller ones. But their size had no impact on tests of social intelligence, such as following human pointing gestures.
Researchers from the University of Arizona's Arizona Canine Cognition Center analysed data from more than 7,000 purebred domestic dogs from 74 different breeds.
For the short-term memory tests, the dogs' owners hid a treat under a plastic cup, while their pet watched. Then they waited 60, 90, 120, or 150 seconds before letting the dog find it. Smaller dogs appeared to find it more difficult to remember where the treat was than larger dogs.
In the test for self-control, owners placed a treat in front of their dog and told them not to take it. Then the owners watched the dog, covered their eyes, or turned away. Generally, larger dogs waited longer before eating the treat.
"The jury is out on why, necessarily, brain size might relate to cognition," said Daniel Horschler, an anthropology doctoral student and lead author of the study.
"We think of it as probably a proxy for something else going on, whether it's the number of neurons that matters or differences in connectivity between neurons. Nobody's really sure yet, but we're interested in figuring out what those deeper things are."
In a blog post for Psychology Today, psychologist Stanley Coren discusses the study. He said that when conducting research for his book "The Intelligence of Dogs," he found that in the top 20% of the dogs ranked for their intelligence, there was only one small toy breed - the Papillon.
A biopsychologist colleague told him this made sense, because the bigger the brain, the more neurons and more connections there are, meaning the animal should be able to process information and store memories better.
Coren said the new study may support this theory, but it should be noted that data was obtained by the public, in what's known as "citizen science," and the tests didn't cover all of the aspects of dog behaviour owners consider intelligence.
In another blog post, biologist Marc Bekoff notes that the words "smart' and "intelligent" don't actually appear in the paper. Rather, it's about "executive functioning," which is what aids productivity.
"There are multiple intelligences in dogs and other animals, and individual differences are to be expected," Bekoff said. He explained it using the example of free-running dogs in Mexico - some were street-smart and could survive in adverse conditions by snatching food, while avoiding dogcatchers, unfriendly dogs, and people. Others were good at "playing" humans and begging for food.
"Conversely, I've known some intelligent, crafty, and adaptable dogs who weren't street-smart and likely couldn't make it in such an environment," said Berkoff. "However, a few with whom I shared my home could easily steal my food and that of the other resident dog in a heartbeat, without either of us knowing what was happening."
He said overall it's unlikely big dogs are smarter than small dogs, because more research is needed, and there are many types of intelligence
"And, of course, individual differences among dogs of all sizes need to be taken into account before any beliefs or grand pronouncements about possible relationships between size and smarts are accepted as facts," he said.
Horschler said he wants to conduct further studies in this area, comparing the cognitive abilities in different breed varieties, like standard and miniature poodles, where one is essentially a larger version of the other.
"I'm really interested in how cognition evolves and how that arises biologically," Horschler said. "We're coming to understand that brain size is in some way related to cognition, whether it's because of brain size specifically or whether it's a proxy for something else."
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