Dogs, it turns out, are brighter than they seem.
A study released this week found evidence of a "general intelligence factor" in dogs.
The study looked at 68 border collies, and found that the ones who were cleverer at one test – for instance, how quickly they could complete an obstacle course – tended to do well at other tests, such as reliably telling which of two plates of food was larger.
Dr Rosalind Arden, one of the authors of the study, told BuzzFeed News it was "very promising evidence" but "just the start", and that more evidence was needed.
A similar thing has also been found in humans. People who are good at maths tend to be good at language, problem-solving tasks, and various other things.
It's not always true – we all know people who are really good at maths but no good with words, say – but, on average, being good at one thing correlates with being good at others.
The dog study is interesting because it shows that dog intelligence might work, and be testable, in a similar way to human intelligence.
At the moment, dog "IQ" testing can take days. Arden and her colleagues' tests take about an hour. "We're excited," she said. "We've shown that there's real promise for a reliable and valid intelligence test for dogs."
And that would mean that we can learn more about human intelligence from watching dogs.
For instance, Arden said, there's a link between how intelligent you are and how long you live. But it's hard to say whether being intelligent makes you live longer.
People who do better on IQ tests also tend to be richer, less likely to smoke, and less likely to drink. It's very hard to account statistically for all the things that might be going on, so it's almost impossible to tell whether it's intelligence that's really causing you to live longer.
But if more intelligent dogs also live longer, "we can get around smoking and diet and exercise, and find out the relationship between lifespan and intelligence," said Arden. "If we were to find that brighter dogs live longer, that would be interesting, because we can't explain it by wealth, or education, or booze, or recreational drugs, or eating too many burgers.
"To a large extent – especially working collies – they have very similar diets and are kept in very similar conditions."
Also, older dogs seem to get dementia in a very similar way to humans.
"Dogs [with dementia] get confused, their appetite changes, their sleep changes, they become socially withdrawn," said Arden. "They also experience the same brain changes."
Scientists have been trying to work out whether dogs can teach us about human dementia. But those efforts "would be advanced if we could find a way of testing dogs quickly – in an hour, instead of 40 days", she says. "It would be a huge advantage if we could scale it up. We could learn an awful lot about brain ageing."
All this would be helpful, because you can study several generations of dogs in the time it takes one generation of humans to grow old. That means you can get much more data, and learn much more, more quickly.
It's definitely true, she said, that some dogs are more intelligent than others. Border collies are "extremely intelligent, amazingly brilliant creatures".
For instance, one collie, Betsy, had a vocabulary of 340 words and could recognise objects from photographs.
Chaser, another collie, was found to have a vocabulary of over 1,000 words.
But it's not just about super-intelligent individuals. "If you just watch an ordinary working sheepdog, it makes the hair on the back of your neck stand up," said Arden.
This isn't the only study that has found similarities between humans and dogs. Another study, published yesterday, found that they learn in some similar ways to us as well.
The study, which was published in PLOS One and also looks at collies, found that dogs with better self-control perform better at some cognitive tests than those with poor self-control. However, it also found profound differences in how dogs can generalise from experience.
Earlier studies have found that, for instance, dogs are capable of deception – which suggests they are thinking about what other minds are thinking.
The realisation that other people (or dogs) have their own consciousness, and don't necessarily know the same things that you do, is quite a complicated thing. Human children don't fully get the hang of it until as late as 4 or 5 years old.