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If you’re a dog lover, you may have heard of Chaser, the border collie who has been called a “genius” and the “smartest dog in the world.” Retired psychology professor John Pilley, Chaser’s owner and co-author of a recent book about her, says he was able to teach her 1,000 words, the largest “vocabulary” of any non-human animal on record.

Dog lovers and handlers alike tend to agree that some canines are quicker to catch-on, learn new tricks, and solve problems than other dogs. But how do we know that one dog is really smarter than another—possessing greater general intelligence—and not just more talented at specific tasks, such as learning words, or more easily trained?

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Despite growing interest in dog cognition over the past 20 years, it wasn’t until very recently that scientists tried to answer this particular question empirically. In May, researchers published findings in the journal Intelligence showing that dogs who perform well on one cognitive test also do well on other cognitive tests—in other words, that dogs may in fact possess a general intelligence factor, or g, like humans. In human intelligence research, individual differences in basic smarts are measured in part by this factor. The better a person performs on a variety of basic cognitive tests—for example, math, science, reading, and writing—the higher their overall g.

Though general intelligence research has been a small, specialized field for nearly a century, interest has taken off as general intelligence is increasingly linked to health in humans, says Rosalind Arden, a research associate at the London School of Economics & Political Science, and one of the lead authors on the study. The finding that dogs may also have a g—and further research into dog intelligence—could help scientists unravel a mystery in the growing field of cognitive epidemiology, the study of how intelligence is linked to health, including lifespan and dementias such as Alzheimer’s. “In humans,” she says, “higher intelligence is associated with many positive health outcomes.”

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Complicating the picture for humans, however, are countless differences between one person and the next in socioeconomic status, culture, lifestyle habits, such as smoking and drinking, as well as parenting styles. All of these variables make it difficult to pinpoint g’s unique contribution to a person’s life-outcomes. “We don’t know if better health in humans comes directly from being brighter, or if it means those who are brighter have other resources and habits that keep them healthy.”

To try to answer this question, Arden turned to man’s best friend. For their study, Arden and co-author Mark James Adams, a researcher at the University of Edinburgh, recruited 68 working border collies trained to herd sheep from local farms in Wales. Border collies are known for their intelligence, Arden says. (One measure of dog intelligence, according to Stanley Coren, a canine psychologist at the University of British Columbia and author of The Intelligence of Dogs, is trainability, and according to surveys of trainers, border collies learn to understand and obey commands more quickly than any other breed of dog.)

“Intelligence is more like ice cream—there are different flavors.”

But Arden and her colleague were most interested in studying this particular group because of the farm dogs’ relative constancy in upbringing and lifestyle. “All were the same breed, ate pretty much the same basic diet, lived in outdoor kennels, and did not have familiarity with toys—in fact, some had never even seen a ball before,” says Arden. “We chose these dogs because we didn’t want to pit the equivalent of human kids from advantaged and disadvantaged backgrounds against one another.”

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Dogs also make great study subjects for intelligence researchers because, unlike most other species, they naturally experience cognitive decline and memory loss as they age. This decline varies widely from one dog to the next, as it does in humans, and dogs develop patterns of neurological damage with dementia that are similar to those found in humans. In the process of domestication, dogs’ diet also began to more closely mirror our own: richer in starch than that of their ancestors, the wolves. It doesn’t hurt either that dogs get along with people, making them easy to work with. (Dogs were the first animals that humans domesticated, and they have remained our closest animal companions for at least 15,000 years.)

If Arden’s hypothesis of general intelligence in dogs proves correct—more large lab studies are needed to support her results—she says examining the potential connections between general intelligence and cognitive decline in canines is the next step. She would ultimately like to identify genetic markers for intelligence and health in dogs. Genes associated with complex traits, like intelligence, are easier to find in dogs than in people because of their longer haplotypes—groups of genes inherited together from a single parent—which means much smaller sample sizes are needed for genomic analyses, she says.

Some researchers disagree with Arden’s findings that dogs may possess general intelligence, with some breeds having a higher g factor than others. Brian Hare, of Duke University’s Canine Cognition Center and citizen science program Dognition, for example, believes dogs possess more than one type of intelligence, rather than a generalized one. In a study published last year in PLOS ONE, using citizen science data, he and his fellow Duke researchers found dogs’ scores on various intelligence tests did not overlap; instead, each dog excelled in one of four unrelated cognitive domains: communication, understanding visual cues, memory, and reasoning.

“I think even studies with people are finding that general measures of intelligence like IQ are obsolete—intelligence is not a glass that is more or less full,” says Hare. “Intelligence is more like ice cream—there are different flavors.”

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Hare, who co-wrote a book called The Genius of Dogs, says he thinks Chaser benefitted from the special training provided by her owner Pilley, who recognized Chaser’s moxie for memorization and problem solving and played games that would build these skills. But Hare admits it’s still possible that certain categories of canine intelligence might be associated with certain health outcomes, though more empirical research would be needed to understand if such a link exists.

In the meantime, Chaser seems to be enjoying her old age. She just celebrated her 12th birthday—most collies live to 13 to 16 years—and despite a recent bout of illness, has recovered nicely, to the relief of her many admirers on Facebook. Her owners say she is in excellent health.

Erica Cirino is a freelance science writer based in New York. She covers wildlife and the environment, and specializes in biology, conservation and policy.

The lead photograph is courtesy of Andrew Smith via Flickr.

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