Last week’s post talked about how dogs can use human social cues like pointing to find hidden food, and that chimps, though more closely related to humans evolutionarily, cannot. How do we explain this?
A major difference between dogs and chimps that could explain their difference in this skill is that dogs just have more experience with humans than chimps do. All the dogs tested on their use of human social cues had interacted with humans since birth. The chimps, though they had exposure to the humans who took care of them in the sanctuary where they lived, arguably had much less interaction with humans than the dogs. So, the factor influencing performance on the food-finding task (and understanding of human social cues) could be the amount of experience an animal has with humans. This theory is called the “human exposure hypothesis”.
One way to evaluate this theory is to test very young puppies on the food-finding task. The puppies, due to their young age, would necessarily have less experience interacting with humans. If the human exposure hypothesis is true, we would expect the puppies’ performance on the task to be worse than older dogs’ performance.
When researchers tested puppies between 9 and 24 weeks of age, they found that they were also able to understand human social cues. Moreover, age (i.e. amount of experience with humans) was not correlated with performance on the task — younger puppies were just as good at the task as older puppies. These findings indicate that the human exposure hypothesis is incorrect, and suggests that the ability to understand human social cues is innate in dogs.
Another possible explanation for the ability of dogs to understand human social cues when chimps cannot is that dogs have been domesticated — they’ve been selectively bred to have characteristics desirable to humans. We don’t know the specific details of how dogs were domesticated, but we do know that they split from their ancestors, gray wolves, about 100,000 years ago.
Researchers tested wolves on the food-finding task and found that they were unable to use human social cues to find the food, indicating that dogs acquired this ability sometime after their split with wolves. This finding supports the theory that dogs evolved the ability to understand human social cues through domestication (this theory is called the “domestication hypothesis”).
So, unlike chimps, it seems that dogs are able to understand human social cues because they’ve been bred by humans to do so. But a couple questions remain:
1. Was the evolution of this skill due to humans specifically breeding wolves that understood human social cues, or was it due to humans breeding wolves based on a more general trait, like behaving friendly towards humans (or, on the other hand, NOT breeding wolves that showed aggression towards humans)?
2. How would you even test the domestication hypothesis, besides spending thousands of years selectively breeding wolves (again)?
Next week’s post will explore the answers to these questions and conclude this series on dogs and human social cues!
Until then, here’s an interesting video that talks a bit about how dogs evolved from wolves and suggests that dogs played an important part in human evolution.
Hare et al. (2002) presents data from both the studies mentioned above, and also briefly discusses a few hypotheses of why dogs can understand human social cues.
Hare, Brian, et al. “The domestication of social cognition in dogs.” Science 298.5598 (2002): 1634-1636.