That special social bond between dogs and humans might be a genetic trait that evolved as dogs became domesticated and diverged from wolves, according to a new study published in the journal Current Biology that looks at the cognitive and behavioral social skills of hundreds of adorable puppies.
“People have been interested in dogs’ abilities to do these kinds of things for a long time, but there’s always been debate about to what extent is this really in the biology of dogs, versus something they learn by palling around with humans,” said co-author Evan MacLean, director of the Arizona Canine Cognition Center at the University of Arizona in Tucson. “We found that there’s definitely a strong genetic component, and they’re definitely doing it from the get-go.”
His co-author, Emily Bray, an anthropology postdoc at the university, has spent the last 10 years studying how dogs think and solve problems, in conjunction with Canine Companions, a California-based service-dog organization catering to people with disabilities. Human children can reason about the physical world and have sufficient social cognitive skills for cooperative communication by the age of 2.5 years, but what about dogs? According to the authors, there is also a growing body of research showing evidence that domesticated dogs share similar social cognitive skills, although possible biological bases for those abilities had not been tested.
MacLean, Bray, and several colleagues thought that if dogs’ skills regarding cooperating with humans were biological (genetic) in origin, then those skills should emerge early in development. So they set about testing that hypothesis with 375 pedigreed, 8-week-old puppies (203 females, 172 males) from February 2017 through June 2020. Drawn from 117 litters, most were Labrador/golden retriever crosses, with 98 pure Labrador and 23 pure golden retrievers rounding out the sample.
All the puppies remained with their mothers until they were weaned (around six weeks) and were kept with their litter mates until it was time to go live with professional puppy raisers for training. Knowing each puppy’s pedigree was key, since the researchers knew how they were all related to one another. This enabled the team to examine whether any differences in the puppies’ abilities might be due to genetic factors. There was also very little human contact (mostly veterinary exams and routine vaccinations), so it was unlikely any communicative behaviors toward humans were learned. This made the doggies ideal subjects for the battery of cognitive and behavioral tests Bray et al. administered.
Following a series of warmup trials so that the puppies would be primed to search for a hidden food reward, the researchers engaged the puppies in four different tasks. In the first, an experimenter hid a treat under one of a pair of overturned plastic cups. Then the experimenter would say “Puppy, look!” and point at the one with the treat, to see if the puppy would respond to the gesture and go find the treat. (A control trial showed that puppies couldn’t find the treat without the social cues, ensuring that they weren’t relying on their sense of smell to find the treat.) There was also a second version of the task: instead of pointing, the experimenter placed a yellow block next to the correct cup, without pointing.
The next two tasks focused on how much or how often the puppies looked at human faces. In the first, the experimenter stood just outside the testing area and spoke to the puppy—following a set script—in a high, singsong-y voice (“who’s a cute puppy?”), and then timed how long the puppy locked gazes with the experimenter. Then the experimenter would move inside the testing area, and if the puppy came within arm’s distance, it would be rewarded with pets.
Finally, the puppies were presented with an unsolvable task. For priming, the experimenter would place a treat inside a container and put a lid on top, then teach the puppy to remove the lid to recover the treat. For the actual test, the experimenter sealed the treat inside the container, then counted how often the frustrated puppy would look to the human for help when it couldn’t remove the lid to access the treat.
The team found that many of the puppies, from a very young age, were responsive to physical and verbal cues and could draw on social contextual cues to find the hidden treats. The puppies would also reciprocate a human’s social gaze. However, when it came to the unsolvable task, very few turned to humans for help in finding the treat. The authors interpret this as evidence that puppies might have an innate ability to respond when humans communicate with them, but the ability for the puppies to initiate communication with humans develops later. This is borne out by studies of adult dogs showing a tendency to look to humans for help. That’s in contrast with wolves, who are more likely to try to solve a problem on their own.
According to Bray, this is similar to the development of human children, who can understand what adults are saying to them before the children themselves can form their own words. “It’s potentially a similar story with puppies,” she said. “They are understanding what is being socially conveyed to them, but the production of it on their end is probably going to take a little bit longer, developmentally.”
The genetic analysis showed that 40 percent of the variation in a puppy’s ability to respond to human cues is genetic; the same holds for variation in meeting gazes during the human-interest task. That’s roughly equivalent to the heritability of intelligence in humans, according to Bray. “From a young age, dogs display human-like social skills, which have a strong genetic component, meaning these abilities have strong potential to undergo selection,” she said. “Our findings might therefore point to an important piece of the domestication story, in that animals with a propensity for communication with our own species might have been selected for in the wolf populations that gave rise to dogs.”
That said, the researchers weren’t able identify the underlying cognitive mechanisms behind the puppies’ responsiveness to human physical and social cues—a matter of considerable debate in the field. Future work will delve more into the specific genes responsible for such traits, based on the cognitive data and blood samples the team has already collected from its furry test subjects.
DOI: Current Biology, 2021. 10.1016/j.cub.2021.04.055 (About DOIs).