Experience or Evolution?

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?

3517862378_43be39f2f6_mA 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.

5532096313_cfaf563c7a_mAnother 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.

Source:

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.

Advertisements

Getting the Point

One of the first things a person does when she or he gets a dog is teach the dog tricks — sit, stay, shake, roll over — so it seems like a given that we humans can communicate with dogs. But can dogs intuit what humans are thinking?

1440335227_0cd32c8213

Most dog owners would unequivocally answer “yes”, and it turns out there’s scientific evidence to back them up. For my first post, I’d like to talk about one of my favorite research areas in animal cognition: the use of human social cues by dogs.

Source: Wobber et al. 2009

The experiment is simple: a person places a piece of food under one of two opaque cups (merely pretending to place the food under the other cup). Next, the person uses some sort of cue (pointing, looking at, etc.) to indicate which cup the food is under. The dog then approaches the cup he thinks contains the food, and the person lifts that cup — if the dog is right, he gets the food as a reward. The whole process is repeated many times and if the dog performs significantly better than chance (he chooses the food “baited” cup more than half the time), then we can conclude that he understood the communicative intent of the cue used by the person (i.e. that the person was indicating where the food was located).

Researchers found that dogs chose the “baited” cup significantly more often when people pointed at, looked at, or tapped that cup. This indicates that the dogs understood not only that the people were using those cues to communicate something, but also WHAT the people were communicating. The dogs had never been trained to associate the cues with finding food — they were able to intuit the intent of the person giving the cue.

This experiment suggests that, at some level, dogs may be able to think about what’s going on in our heads. That’s a fascinating finding in and of itself (though probably an obvious one to dog owners), but here’s where it REALLY gets interesting.

Researchers tried the same experiment with chimpanzees, one of our closest genetic relatives.

Ape Family Tree

[Slight tangent: The cognitive abilities of chimps and other primates are often studied in order to better understand the evolution of human cognitive abilities. If chimps share a particular cognitive ability with humans, then we can infer that that ability evolved before humans and chimps evolved into separate species. If, on the other hand, humans have a cognitive ability that is not shared with chimps, then that ability probably evolved after chimps and humans separated on the evolutionary tree.]

So researchers wanted to see if chimps could also understand human social cues. They did the exact same experiment as was done with the dogs, but the results were very different: the chimps were unable to use humans’ gestures to find the food!

These results posed an interesting puzzle: how are dogs able to use human social cues, while our closest evolutionary and genetic relatives cannot?

The answer to that question is another blog post in itself (at least), so check back here next week for that! In the meantime, here’s a video that’s a nice summary of everything in this post (including a demo of the experiment). The researcher in the video is Dr. Brian Hare, who runs the Canine Cognition Center at Duke University. He conducted one of the first studies investigating dogs’ understanding of human social cues (Hare et al. 1998), and has since done many experiments extending that research.

For those interested in reading the original scientific papers of this research, Hare et al. (2002) is a great place to start — it includes comparison experiments between dogs of different ages, dogs and chimps, and dogs and wolves (preview for next week!). You can find most of Dr. Hare’s papers on canine cognition (including those mentioned above) here.

Other related papers:

Agnetta, Bryan, Brian Hare, and Michael Tomasello. “Cues to food location that domestic dogs (Canis familiaris) of different ages do and do not use.” Animal cognition 3.2 (2000): 107-112.

Itakura, Shoji, et al. “Chimpanzee use of human and conspecific social cues to locate hidden food.” Developmental Science 2.4 (1999): 448-456.

Miklósi, Ádám, et al. “Use of experimenter-given cues in dogs.” Animal Cognition 1.2 (1998): 113-121.