When Less is Worth More

Often when problem solving, we don’t have the time or cognitive capacity to painstakingly evaluate each solution. Instead, we make an educated guess or rely on our common sense or a rule of thumb. These shortcuts (called “heuristics”) may save us time and cognitive processing, but they don’t always lead to the optimal solution.

Take, for example, the “less is better” effect: valuing a single, high quality object more than that same high quality object plus an object of lower quality. The addition of the lower quality object somehow decreases the subjective value of the higher quality object, even though the quantity of the two objects is greater than the high quality object alone.

286px-HFG_Hans_(nick)_Roericht-_TC100-_dish_set-dhubThis may seem ridiculous, but humans have clearly demonstrated this effect. In one experiment, Hsee (1998) asked participants to indicate how much they would be willing to pay for a set of dishes. In one condition, the set contained 24 dishes. In another condition, the set contained 40 dishes, but 9 of them were broken. Even though the second condition contained more unbroken dishes than the first, the amount that participants were willing to pay for the first set was greater than for the second set. The inclusion of some broken dishes decreased the value of the second set, even though it actually contained more unbroken dishes than the first set.

It’s important to note that participants weren’t comparing the two sets of dishes directly; each participant was only asked to name a price for one set of dishes. Their responses, then, were based on their valuation of the particular set of dishes without additional information or comparison.

When Hsee asked participants to name prices for both sets of dishes, the “less is better” effect disappeared. Instead, participants said that they would pay more for the larger set of dishes than the smaller one. This indicates that humans use comparison information (when it’s available) to make valuation judgments, and we can use this information to overrule heuristics and arrive at the optimal choice. But when we don’t have that comparison information, our heuristics can sometimes steer us wrong.

What about nonhuman animals? Do they rely on similar heuristics when problem solving, and thus make similar suboptimal choices?

Kralik et al. (2012) investigated whether rhesus macaques would also demonstrate the “less is better” effect. In both the lab and a more naturalistic setting, they gave the macaques two options: a more-preferred treat (like a grape), or a more-preferred treat AND a less-preferred treat (like cucumber).

8774415224_ac7e9deb0e_mThey found that the macaques chose the grape alone significantly more than the grape + cucumber. At first glance, this doesn’t make sense; when given the choice between more food and less food, it’s more evolutionarily advantageous to choose more food. However, it seems that the macaques were more concerned with the quality of the choice than the quantity, and somehow the presence of the less-preferred cucumber lowered the quality of the more-preferred grape. So the decision was instead between lower-quality food (grape + cucumber) and higher-quality food (grape).

It turns out that focusing on quality more than quantity might actually make evolutionary sense: research on the foraging behavior of animals suggests that, when food is scarce, focusing on the quality of food in a particular location (rather than quantity) may lead to more optimal foraging decisions (Do I keep eating at this tree or move on to another one?). Additionally, when food is abundant, averaging the quality of all the food in a particular location will maximize outcome.

So it seems that when solving this problem, macaques rely on a heuristic that may maximize outcome in the wild, even though it doesn’t maximize outcome in this particular task. And, unlike humans, macaques aren’t able to use comparison information to override the heuristic and make the optimal choice. Perhaps factoring in comparison information requires higher cognitive processes that macaques don’t possess, or perhaps macaques just need more experience with the task in order to factor in comparison information.

2802429078_ec607610f9_mEither way, the results of these experiments suggest that some heuristics may have an evolutionary origin that predates the split between humans and other primates. And they may have developed even earlier than that: Pattison & Zentall (2014) recently found that dogs also demonstrate the “less is better” effect!

If you’ve enjoyed reading about animal cognition research on this blog, check out Inside Animal Minds, a short NOVA series on animal cognition. The first episode airs tonight at 9 pm on PBS!


Sources Cited:

Hsee, Christopher K. “Less is better: When low-value options are valued more highly than high-value options.” Journal of Behavioral Decision Making 11.2 (1998): 107-121.

Kralik, Jerald D., et al. “When less is more: Evolutionary origins of the affect heuristic.” PloS one 7.10 (2012): e46240.

Pattison, Kristina F., and Thomas R. Zentall. “Suboptimal choice by dogs: when less is better than more.” Animal cognition (2014): 1-4.

fMRI in Dogs

We can learn a lot about animal cognition by using behavioral experiments, where we rely on the actions of an animal in a particular situation to infer what processes are occurring in the animal’s brain. But what about looking more directly at what the brain is doing?

One way to do that is to record the activity of neurons in the brain using electrodes. There are a few downsides to this method, though. First, neural recordings can only show us the activity of very small areas of the brain at a time. Additionally, the animals used in these experiments have usually been raised in a lab, rather than in their natural environment, which could affect their cognitive development.


MRI Machine

Another way to look at brain activity is through imaging such as functional Magnetic Resonance Imaging, or fMRI. The MRI machine uses a magnetic field to look at oxygen flow to different areas of the brain. More active brain areas need more oxygen, so by tracking the oxygen flow to the brain over time, we can determine the pattern of activity in the brain. And, unlike with neural recordings with electrodes, we can look at the activity of the entire brain at once.


Unfortunately, fMRI requires that the person (or animal) being scanned lie completely still inside the MRI scanner, which is a bit confining and noisy. While this isn’t a problem for anesthetized animals, it’s nearly impossible for awake animals. But recently, researchers have made incredible progress in using fMRI to study dogs.

In 2012, a group of researchers managed to train two dogs to lie still in an MRI machine long enough to have their brains scanned. They first got the dogs used to laying with their chins in a chin rest, then slowly acclimated them to the noise of the machine, ear muffs (to muffle some of the machine’s noise), and the MRI machine itself. While in the scanner, the dogs were shown two different hand signals: one was followed by a food reward (“reward”), while the other was not (“no reward”).

The researchers were interested in the response of an area of the brain called the caudate nucleus. Among other important functions including voluntary movement and learning, the caudate nucleus in involved in the reward system of the brain; previous studies have found that the caudate becomes more active when a reward is expected.

2241616932_107199f0fa_mSure enough, the researchers found that the dogs’ caudate nuclei were more active when the “reward” hand signal was given than when the “no reward” signal was given. They later replicated this study with 11 more dogs and found that the increase in activity in the caudate was comparable to that found in humans. Interestingly, some of the dogs studied were service dogs, and they had nearly significantly greater caudate activation than the non-service dogs when the “reward” hand signal was given. The researchers theorized that, due to their extensive training, the service dogs may have found the hand signal itself intrinsically more rewarding.

(Check out the Supporting Information for the first paper for an interesting video detailing the training that the dogs underwent!)

Before these studies, fMRI studies with animals required that they be restrained or anesthetized, both of which could greatly affect brain activity. Believe it or not, researchers actually ran studies investigating brain activity in response to odors…in anesthetized dogs! While the brain does respond to such stimuli even under the influence of anesthesia, it clearly does so in a different way than it would normally. (Of course researchers were aware of this, but there just wasn’t another option at the time.)

Once it had been shown that dogs could be trained to lie still in an MRI machine, some researchers decided to see just how different the brain’s response to odors is in anesthetized and awake dogs. They found that, in addition to the sensory brain areas active in anesthetized dogs, the frontal cortex was activated by odor in awake dogs. (The frontal cortex is implicated in complex cognitive functions like decision-making and planning.) The researchers suggested that the frontal cortex activity could be involved in understanding what an odor means in a particular context, and could inform how the dog behaves in response to that odor. Understanding this kind of brain activity could have major implications for how we train drug- and bomb-sniffing dogs.

443627085_4fe6f95f01_mThe first group of researchers also studied dogs’ brain activity in response to odors. They presented dogs with five different odors: a familiar dog, an unfamiliar dog, the dog itself, a familiar human, and an unfamiliar human. They found that, compared to the other four odors, there was greater activity in the caudate nucleus in response to the familiar human odor. This indicates that not only could the dogs discriminate between the different odors, but that they also associated that particular human with reward. And again, the researchers found that the response was stronger in service dogs, possibly due to their more extensive human contact during training.

Finally, another group of researchers compared the brain activity of humans and dogs as they were listening to human and dog vocalizations and natural sounds. They found that similar areas of the brain were more active when they heard the vocalizations of conspecifics (i.e. when humans heard humans and dogs heard dogs). This suggests that these brain areas may have evolved for that particular purpose more than 30 million years ago (although convergent evolution is a possibility). Additionally, some brain areas responded more strongly to more positive vocalizations (i.e. laughing versus crying). These brain areas were in similar locations in both dogs and humans, and responded to both species’ vocalizations. This suggests that dogs and humans may have comparable emotional processing of sounds.

Interestingly, part of the training of the dogs used in this study involved social learning – naïve dogs watched an experienced dog get in the MRI scanner and receive praise and treats, which motivated the naïve dogs to behave in the same way!

(Although the paper of this study isn’t freely available, the researchers did make a fascinating video summarizing their study, and NPR wrote an article about it.)

4840054871_b79aef16f2_mStudying canine cognition using fMRI is a relatively new application of the method, but the research so far looks promising. Not only will it allow us to get a direct look at what’s going on in dogs’ brains, but it could also improve the way we train service dogs and care for our best friends.


I’ll end with a thought-provoking quote from one of the above papers, about canine cognition research:

“…While the study of the canine mind is fascinating for its own sake, it also provides a unique mirror into the human mind. Because humans, in effect, created dogs through domestication, the canine mind reflects back to us how we see ourselves through the eyes, ears, and noses of another species.”

-Berns et al. (2012)


Sources Cited:

Andics, Attila, et al. “Voice-Sensitive Regions in the Dog and Human Brain Are Revealed by Comparative fMRI.” Current Biology (2014).

Berns, Gregory S., Andrew M. Brooks, and Mark Spivak. “Functional MRI in awake unrestrained dogs.” PloS one 7.5 (2012): e38027.

Berns, Gregory S., Andrew Brooks, and Mark Spivak. “Replicability and Heterogeneity of Awake Unrestrained Canine fMRI Responses.” PloS one 8.12 (2013): e81698.

Berns, Gregory S., Andrew M. Brooks, and Mark Spivak. “Scent of the Familiar: An fMRI Study of Canine Brain Responses to Familiar and Unfamiliar Human and Dog Odors.” Behavioural Processes (2014).

Jia, Hao, et al. “Functional MRI of the Olfactory System in Conscious Dogs.” PloS one 9.1 (2014): e86362.

Mission Accomplished

Have you ever noticed, upon achieving a goal, the rewarding sense of accomplishment that is completely separate from the goal itself? Completing a task or achieving a goal seems to be rewarding in itself, independent of the actual outcome of that task or goal. Do other animals feel this sense of accomplishment after achieving a goal? A recent study suggests that dogs might.

In their study, McGowan et al. (2013) investigated how dogs reacted to rewards after solving a puzzle compared to receiving a reward randomly. First, they trained dogs to solve various puzzles, such as pressing a lever or pushing a box over, in order to get a reward.

160px-Beagle_puppy_CadetDuring the testing phase, a dog would be led into a room containing a puzzle. In the experimental condition, the puzzle was one that the dog had been trained to solve. Once the dog solved the puzzle, a door would open, allowing the dog to access the reward. In the control condition, the puzzle was completely new to the dog, who had no idea how to solve it. The door to the reward would open randomly, regardless of what the dog did. The important difference between these two conditions is that in the first (experimental), the dog had control over access to the reward, whereas in the second (control), she did not.

The dogs were tested on six trials per day for six days (three days in the experimental condition, three in the control condition). Having all the dogs participate in both conditions allowed the experimenters to control for individual differences in the dogs’ temperaments.

McGowan et al. closely examined and compared the behavior of the dogs in the two conditions and made some interesting findings. First, they found that dogs in the experimental condition wagged their tails more frequently than dogs in the control condition. Conversely, dogs in the control condition chewed on the puzzle devices, but dogs in the experimental condition did not.

3059800422_015f4c45c4_mWe can easily interpret the tail-wagging results: clearly, the dogs were in a more positive emotional state while in the experimental condition than while in the control condition. The chewing behavior is a bit more difficult to interpret, but McGowan et al. suggest that it was the result of the dogs’ frustration with their inability to open the door by solving the puzzle.

Both of these behaviors were measured before the door to the reward was opened, so they can’t be attributed to receiving the reward. Rather, they suggest that the differing emotional states of the dogs in the two conditions were due to the dog solving the puzzle (or not).

(Note: Animal emotions are a source of conflict among researchers. Some insist that nonhuman animals do not have emotions, others say that they have emotions but they aren’t the same as human emotions, still others assert that nonhuman animals have the same emotions as humans, and many more researchers fall somewhere in between. For the purposes of this blog post, I’ll stick with the very vague term “positive emotion” to describe the canine equivalent of “sense of accomplishment”.)

A particularly interesting result is that in the experimental condition, the dogs were excited to go to the testing room at the start of each trial. However, in the control condition, while they showed excitement on the first couple trials, the dogs became reluctant to go to the testing room in later trials. McGowan et al. think this could be due to apathy caused by the dogs having no control over their environment (i.e. opening the door to the reward).

Overall, these results indicate that dogs, like humans, experience a positive emotion after achieving a goal that is separate from the direct result of achieving that goal (in this case, the reward). Furthermore, the behavior of the dogs in the control condition suggests that a sense of having control over the environment may play a part in this positive emotion. Which makes sense, when you think about it. If we assume that feeling like you have control over your environment is an important component of happiness or wellbeing, then achieving a goal or completing a task (i.e. changing your environment in a self-defined way) should cause a positive emotion.


McGowan et al. also used three different rewards (food, human contact, and canine contact) and compared the dogs’ responses – check out their paper for the interesting results!

Source Cited:

McGowan, Ragen TS, et al. “Positive affect and learning: exploring the “Eureka Effect” in dogs.” Animal cognition (2013): 1-11.

Letting the Cat Out of the Bag

I’ve talked a lot on this blog about canine social cognition, but what about feline social cognition? That may sound a bit oxymoronic to some, but cats, like other domesticated species, live closely alongside humans, so it makes sense that they could have social cognitive abilities.

However, an important difference between cats and other domesticated species lies in the domestication process itself: whereas most domesticated species were actively domesticated by humans through artificial selection, researchers hypothesize that cats were domesticated through natural selection. Unlike dogs, which could be trained to aid humans with hunting, herding, etc., cats had little usefulness to humans (except maybe killing rodents, which could also be accomplished by dogs). Cats were actually probably first attracted not to humans, but to the mice and rats that infested their fields and grain stores. The cats that were least averse to humans were more likely to hang around humans in order to have greater access to rodents. These less-averse cats then bred with each other, causing successive generations of cats to be less and less averse to humans. Cats essentially selectively bred themselves the same way Dmitri Belyaev selectively bred silver foxes.

The upshot of this difference in domestication between cats and other species is that cats weren’t bred to work with humans; rather, they were bred to be less averse to humans. This is basically the difference between cooperating and tolerating. And although both characteristics allow cohabitation with humans, being tolerant doesn’t entail the possession of any social cognitive abilities.

Fortunately for us, some researchers have investigated the influence of the differential domestication in cats and dogs by directly comparing their performance on social cognition tasks. Miklosi et al. (2005) first tested cats and dogs on the hidden food task, where a human indicates the location of food by pointing at it. Cats, like dogs, were able to understand the human social cue of pointing to find the food.

CatMiklosi et al. then observed cats’ and dogs’ behavior in a task where the food was impossible to access (very similar to this study). While dogs looked to humans for help, cats rarely did so.  Taken together, these results suggest that cats can understand human social cues, but are unable to communicate with humans.


A more recent study investigated whether cats could recognize the voice of their owner. Saito & Shinozuka (2013) played recordings of people saying a cat’s name and examined the cat’s response. In order to gauge recognition, the researchers used what’s called a habituation task. The basic principle behind a habituation task is that if you experience a stimulus enough (many times or over a prolonged period), your response to that stimulus will decrease. For example, when you first hear a fire alarm, you instantly become alert, adrenaline rushes through your body, etc. However, if the alarm goes on long enough and nothing else happens, your body will return to normal. Similarly, when you first put on clothes in the morning, you’re probably aware of how they feel against your skin for a minute or two, but then you stop noticing. Habituation is the brain’s way of filtering out unimportant stimuli so you can focus on the important stuff. In a habituation task, experimenters habituate a subject to a stimulus, then change the stimulus in some way and see how the subject responds. If the subject perceives the stimulus as different, then her response will be comparable to the first time she heard the habituation stimulus. If she doesn’t perceive the stimulus as different, then she will have little or no response.

For each cat, Saito & Shinozuka played three recordings of different strangers saying the cat’s name, followed by a recording of the owner saying the cat’s name. They were interested in comparing the cat’s habituated reaction to the third recording (a stranger) and the potentially different fourth recording (the owner). If the cat has a greater response to the owner’s recording than the third stranger’s recording, then he probably recognizes his owner’s voice.

The researchers found that overall, the cats had a greater response to their owners’ recordings than to the third strangers’ recordings, demonstrating that they recognized their owners’ voices. Interestingly, the responses were limited mostly to ear and head movements – no cats actually stood up and moved toward the sound. (The media have had some fun with this result – here’s an informative but slightly biased video about the study and its results.)

So it seems that although cats are domesticated and can understand some human social cues, they may not have all the social cognitive abilities of dogs, and this is likely due to their domestication through natural selection.

I’ll leave you with a video about an interesting study comparing the relationships between humans and cats, dogs, and babies. Do the results fit with our hypotheses about dog and cat domestication?

Sources Cited:

Miklósi, Áam, et al. “A comparative study of the use of visual communicative signals in interactions between dogs (Canis familiaris) and humans and cats (Felis catus) and humans.” Journal of Comparative Psychology 119.2 (2005): 179.

Saito, Atsuko, and Kazutaka Shinozuka. “Vocal recognition of owners by domestic cats (Felis catus).” Animal cognition (2013): 1-6.

If you’re interested in reading more about domestication, here’s an interesting paper:

Driscoll, Carlos A., David W. Macdonald, and Stephen J. O’Brien. “From wild animals to domestic pets, an evolutionary view of domestication.” Proceedings of the National Academy of Sciences 106.Supplement 1 (2009): 9971-9978.

Looking for Help

4672605862_659b404a08_nMany dog owners would agree that there are few things more tragic to a playing dog than the ball rolling under the couch. Whenever it happened to my dog when I was in the room, she would look up at me, then back to the ball in what seemed like a silent plea for assistance. Of course, appearances can be deceiving. Some scientists argue that this human-directed gaze behavior, rather than being a form of intentional communication, is a learned response to certain situations: Based on previous experience, the dog has learned that when a desired object is out of reach, looking at a human leads to that object being moved within reach.

Marshall-Pescini et al. (2013) investigated this issue by giving dogs a task that, though first possible, became impossible in a later trial. They wanted to see if and how the dogs’ human-directed gazing behavior changed when the task became impossible. The task was to obtain food that was placed under an overturned, transparent Tupperware container. The food and container were placed on a board, so the food could be obtained using various strategies (e.g. turning the container over, pushing the container off the board). The first three trials were solvable, as the container was merely placed over the food. However, in the fourth trial, the container was attached to the board, making the task unsolvable. During all the trials, the dog’s owner (the “caregiver”) stood about a foot away from the board, facing it, while an experimenter also stood about a foot away from the board, adjacent to the owner.

Merely comparing the dogs’ behavior in the solvable and unsolvable trials would not rule out the theory that their human-directed gaze behavior is a learned response, so Marshall-Pescini et al. added a second condition. In the first condition (Attentive), both the owner and experimenter faced the board. In the second condition (Back), the owner faced the board, but the experimenter faced away from the board. If dogs’ human-directed gazes are a form of intentional communication, then presumably the dogs would gaze more at the person actually looking at them and the container. (This, of course, requires the dogs to understand that communication requires attention, or, at the very least, eye contact.)

Marshall-Pescini et al. also conducted this study with very young, preverbal children (15-27 months old), so they could directly compare dogs to humans. In this part of the study, the caregiver was the children’s nursery school teacher.

6872677550_318f2e60f0_nMarshall-Pescini et al. found that, in the unsolvable trials, both the dogs and the toddlers increased alternating their gaze between the caregiver and the container, compared to the solvable trials. Additionally, in the Back condition, they gazed more at the caregiver (who was facing the board) than at the experimenter (who was facing away from the board).

These results suggest that the human-directed gaze behavior of dogs (and toddlers) really is a form of intentional communication, rather than a learned response. We’ve already seen that dogs can understand human communication, but it seems that dogs can intentionally communicate with us, too!

(Although the overall results were the same, there were a few interesting differences in gazing behavior between the dogs and toddlers. For example, in the Attentive condition, dogs looked at both the experimenter and the caregiver for help, but toddlers looked at the experimenter much more than the caregiver. Marshall-Pescini et al. attribute this difference to some important discrepancies in environmental factors when testing the toddlers and dogs. First, the dogs were tested in a completely unfamiliar room, whereas the toddlers were tested in a room at their nursery school. Second, the “caregiver” in the dog experiment was the dog’s owner, while it was a nursery school teacher in the toddler experiment. How might these factors have caused the differences in gazing behaviors of the dogs and toddlers?)


Marshall-Pescini, S., et al. “Gaze alternation in dogs and toddlers in an unsolvable task: evidence of an audience effect.” Animal cognition (2013): 1-11.

What the Fox Say?

(I know, I know, I couldn’t help myself)

Last week’s post ended with a couple remaining questions about how dogs understand human social cues:

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)?

small__3198737613One fascinating study that addresses both of these questions is the Russian Fox Experiment. The experiment began in 1959, when Soviet scientist Dmitri Belyaev started breeding silver foxes for tameness. He would only breed those foxes that showed the most friendliness and least aggression towards humans. After generations of this selective breeding, the foxes behaved very much like dogs: they were eager to be around humans, wagged their tails, and even evolved floppy, dog-like ears! This experiment is essentially the domestication of the silver fox, and likely parallels the domestication of the dog.

(For more information about this experiment, including some great pictures and videos, check out this fantastic post on The Thoughtful Animal, an animal cognition blog on Scientific American’s website.) (Edited: That post’s author, Jason Goldman, wrote another version of that post, which goes into more detail about the history of the experiment.)

Fortunately for our purposes, the Russian Fox Experiment is still going strong. Since we know exactly which traits the domesticated silver foxes are bred for, testing them on the food-finding task could tell us whether selectively breeding for tameness alone is sufficient to develop the skill of understanding human social cues.

When researchers tested domesticated silver fox kits and adults, they found that the foxes were just as good as dogs on the food-finding task. Undomesticated “control” silver foxes, which had not been selectively bred for any trait, performed worse on the task than the domesticated silver foxes and the dogs. These findings indicate that the domesticated silver foxes developed the ability to understand human social cues through domestication, which is the same process we theorize for dogs (the domestication hypothesis).

Furthermore, the results suggest that selectively breeding for tameness alone is sufficient for developing the ability to understand human social cues. In other words, we didn’t need to specifically breed foxes or dogs for this specific trait — we could just breed them for the more general trait of tameness, and the trait of understanding human social cues was part of the package.

There is evidence, however, that this ability can be improved by more specific selective breeding. Researchers ran the food-finding task yet again, this time comparing the performance of working dogs (shepherds and huskies) and non-working dogs (basenjis and toy poodles). Working dogs have theoretically been bred to cooperate with humans, whereas non-working dogs have not. The working dogs did perform significantly better than the non-working dogs on the food-finding task, showing a greater ability to understand human social cues.


Together, the results of these studies suggest a mechanism for the evolution of the ability to understand human social cues in dogs: domestication by selectively breeding for tameness was sufficient to develop this ability, and additional selective breeding can improve this ability, for example in working dogs.

Thanks for sticking with me through this (longer-than-originally-planned) series of posts — hopefully it was interesting and gave you something to think about! Next week we’ll move on to another area of animal cognition.

I’ll leave you with this timely Op-Ed on LiveScience called “Does a Dog’s Breed Dictate Its Behavior?”.


Goldman, Jason. “Monday Pets: The Russian Fox Study.” The Thoughtful Animal. Scientific American, 14 June 2010. Web. 1 Oct. 2013.

Hare, Brian, et al. “Social cognitive evolution in captive foxes is a correlated by-product of experimental domestication.” Current Biology 15.3 (2005): 226-230.

Wobber, Victoria, et al. “Breed differences in domestic dogs'(Canis familiaris) comprehension of human communicative signals.” Interaction Studies 10.2 (2009): 206-224.


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.


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.