Dolphin Hear, Dolphin Do

They say that imitation is the sincerest form of flattery, but in fact it’s an important method of learning. When young children play house or pretend to talk on the phone, for example, they’re trying out and learning important cultural and social behaviors. Additionally, scientists think the ability to imitate may be required for higher, human-specific cognitive abilities, such as language and theory of mind (understanding what others may be thinking). As we’ve seen before, scientists often study cognitive abilities of animals in order to better understand those abilities in humans. We can study imitation in animals because, importantly, imitation doesn’t require the use of language.

7376861816_2b39b2b644_nInterestingly, dolphins appear to be very good at imitating the sounds and motions of other dolphins and of humans. This finding surprised scientists because dolphins and humans are only very distantly related. Scientists suspect that dolphins’ ability to imitate is the result of convergent evolution (different species evolve the same characteristic or ability, independent of each other), rather than the very early evolution of this ability by a common ancestor of humans and dolphins. By studying imitation in dolphins, we can gain some insight into how and why humans may have also developed this ability.

However, it is possible that in dolphins, imitation isn’t a conscious copying behavior (like it is in humans). Rather, their imitation could be due to an automatic process called “response facilitation”. Put simply, response facilitation is when an animal that senses another animal make a familiar movement becomes more likely to make that movement itself. This occurs because there is a strong connection in the animal’s brain between a movement and the sound made by that movement, due to all of the experience the animal has of making that movement itself and hearing the corresponding sound. In response facilitation, the animal’s response is less conscious and deliberate, and is instead more like a reflex.

In order to investigate the nature of dolphins’ imitation ability, Jaakkola et al. (2013) studied the perceptual information used by a blindfolded dolphin when imitating the motions of another dolphin and a human. Specifically, the researchers studied when the blindfolded dolphin relied on sounds and on echolocation to determine the motions made by the other dolphin and the human.

Jaakkola et al. assumed that a dolphin would be very familiar with the sounds made by a dolphin doing certain motor actions (such as blowing bubbles, spinning in a circle, and waving). Therefore, sound alone should be sufficient for the blindfolded dolphin to figure out the motion that another dolphin (the dolphin “model”) is making, in order to imitate it. This does not rule out the possibility of response facilitation, which is where the human “model” comes in: a dolphin should be much less familiar with the sounds made by a human doing certain motor actions. Thus, it should rely more on echolocation (which provides information about the position of the human model) to figure out the motion that the human model is making.

8191515204_edd9e9199e_nThe use of echolocation to imitate humans would indicate that dolphins’ imitation is not due to response facilitation for a couple reasons. First, a dolphin’s sense of echolocation, unlike its other senses, is not always on: the dolphin has to decide to use echolocation. The use of echolocation, then, suggests that the dolphin is consciously trying to determine the human’s movements, rather than using response facilitation. Second, dolphins can’t use echolocation to gauge their own movements, so that information isn’t connected to that movement in the dolphin’s brain. Thus, echolocation information for a particular movement shouldn’t automatically trigger that same movement in the imitating dolphin.

Jaakkola et al. trained a dolphin to imitate the motions of another dolphin and a human, while blindfolded (which is an incredible feat in and of itself!). They found that the dolphin was able to imitate both the other dolphin and the human more accurately than chance, and that the dolphin was equally accurate when imitating the other dolphin and the human. However, the dolphin used echolocation significantly more when he imitated the human than when he imitated the other dolphin.

This result indicates that imitation by dolphins is not due to response facilitation, but is instead more like the imitation ability of humans. The fact that the dolphin was able to use hearing and echolocation in varying proportions also shows how flexible and intentional their imitation can be: they can use different sources of information in order to imitate, and they can select the most appropriate information sources depending on the situation.

The Dolphin Research Center, where this study was carried out, made some great summary videos of this research: here’s one of the study where they trained the dolphin to imitate another dolphin while blindfolded, and here’s one of the study described above.


Jaakkola, Kelly, et al. “Switching strategies: a dolphin’s use of passive and active acoustics to imitate motor actions.” Animal cognition (2013): 1-9.

Will Work for (Equal) Pay

Scales_of_Justice_(PSF)One important concept we possess at a young age is fairness (as any parent of multiple children will confirm!). Children especially do not hesitate to speak up (or, more often, whine) if they detect inequality, and much of our society focuses on achieving fairness for all. Given the sociality of some animal species, could these animals also have a concept of fairness?

Brosnan & de Waal (2003) investigated whether capuchin monkeys (who are considered very social) conceptualize fairness. (The term most researchers use is “inequality aversion”, since they’re not sure if it is actually the same as the human concept of fairness. For simplicity, I’ll continue to call it “fairness”.) They first taught the capuchins an exchanging task, where the researcher gives the monkey a token (e.g. a rock), which the monkey then hands back to the researcher in exchange for a treat.

Once the capuchins learned this task, Brosnan & de Waal wanted to see how they would react to getting a less desirable treat than another capuchin in the same task. It seems obvious that they would be upset – they’re doing the exact same task as the other capuchin, so they should also get the more desirable treat (equal “pay” for equal “work”). But think about the thought processes required for such a reaction: the capuchin must not only pay attention to the task the other capuchin does, but also recognize that it is the same task she does. Then she has to see what treat the other capuchin gets, and then realize that it is better than the treat she gets. Finally, and most importantly, she has to CARE about that disparity – this is what we call fairness (and what researchers call inequality aversion).

In order to study fairness in capuchins, Brosnan & de Waal did the exchange task with two capuchins that were in separate, side-by-side enclosures. There were no opaque barriers between the enclosures, so capuchins could clearly see each other doing the task. In the inequality condition of the exchange task, one of the capuchins would always receive a grape (a more preferred treat), and the other capuchin would always receive a piece of cucumber (a less preferred treat). As a control, the researchers also conducted sessions of the task where both capuchins got the same treat.

small__5546971563Brosnan & de Waal found that in the inequality condition, the capuchin receiving the cucumber often refused to do the exchange task, either by refusing to return the token or refusing to take the treat (here’s a short clip showing a hilarious example of this – I highly recommend watching it!). These “non-exchanges” occurred on about 40% of trials in the inequality condition, but only about 5% of trials in the control condition (when both capuchins got the same treat). So when the researcher wasn’t playing fair, the cheated capuchin often refused to play at all!

The researchers decided to do the same task, but with an even bigger disparity. This time, instead of merely giving the capuchins unequal pay for equal work, the capuchin receiving the grape didn’t have to work for it at all – she was just given the grape, while the other capuchin still had to exchange for the cucumber. In this condition, non-exchanges by the cucumber capuchin increased to around 80% of trials!

The results of these two experiments suggest that capuchins do have some concept of fairness, though it may not be exactly like the concept of fairness that humans have. In a final experiment, Brosnan & de Waal investigated the effect of the mere presence of a grape on the cucumber capuchin’s reaction. They tested only one capuchin at a time, making her exchange for a piece of cucumber, and placing a grape in front of the (empty) adjacent enclosure. The results were similar to the first experiment: the capuchin refused to exchange in about 40% of the trials.

This suggests that their concept of fairness may not require equal treatment relative to other capuchins. Rather, their concept may only require that a better reward exists, regardless of whether another capuchin is receiving that reward.

Overall, these results suggest that some kind of concept of fairness may be innate in primates (including humans). However, evolutionarily, the capuchins’ behavior seems a bit puzzling: If you’re trying to survive, you should take whatever food you can get, rather than refuse it because something better exists (especially if you wouldn’t get that better food anyway). How could this behavior be evolutionarily advantageous? (Hint: Think about why the researchers did this experiment with capuchins in the first place.)

A lot of work research on fairness in primates has been done since Brosnan & de Waal published their results. Here’s a recent review of that literature, for those who are interested (unfortunately, the article isn’t available for free, but hopefully those affiliated with a university or research institute can access it).

(The clip I linked to above is taken from de Waal’s fascinating TED Talk on moral behavior in animals – check it out!)


Brosnan, Sarah F., and Frans BM De Waal. “Monkeys reject unequal pay.” Nature 425.6955 (2003): 297-299.

One Fish, Two Fish

Counting is an ability that humans use every day, often without thinking about it: paying for purchases, measuring out sugar for your coffee, and calculating just how much longer until lunch. But do animals possess this ability too?

It would make sense for animals to have a ratio-based ability to determine amounts; that is, given two different amounts of an item (such as food), it would be evolutionarily advantageous if they could determine which amount is largest.

Humans and other animals actually do use a ratio-based system, and there’s an intuitive rule about how it works: Weber’s Law states that as the ratio between quantities gets smaller, discrimination becomes more difficult. Which makes sense, since it’s more difficult to discriminate between 7 items and 8 items than between 7 items and 20 items.

7 vs. 8 dots

7 vs. 20 dots





It turns out that for small amounts (less than 4 items), some animals (including humans) can accurately discriminate between them regardless of their ratio (they discriminate between 1 and 2 items just as accurately as between 1 and 3 items). This indicates that another, number-specific system may be used when discriminating between small numbers of objects.

Some interesting research has been done on how humans use these two number systems, and it appears that the systems are independent of each other (one or the other system is used while making a numerical judgment, but not both).

Researchers discovered this by assessing how well human infants could discriminate between different quantities of objects. They found that infants can accurately discriminate between large quantities, as long as the ratio between those quantities is sufficiently large. But when quantities are small (less than 4 items), infants can accurately discriminate between them, even if the ratio between those quantities is small (i.e. 2 items vs. 3 items).

Here’s the result that really clinches the independence of these two number systems: infants cannot discriminate between quantities that span the small quantity – large quantity boundary. So while they can discriminate between 1 and 2 items, or 1 and 3 items, or 2 and 3 items, they cannot accurately discriminate between 1 and 4 items, or 3 and 6 items (remember that the number-specific system is only used for quantities less than 4). This indicates that the two number systems can’t be used together – they’re independent.

[An important feature of these two systems is that they’re nonverbal (don’t involve the use of language). Having verbal numerical labels obviously makes numerical discrimination easier, and it helps explain why older humans can easily discriminate between quantities that span the small quantity – large quantity boundary.]

The research on these two number systems in non-human animals has yielded conflicting results, so I’m just going to discuss one really interesting recent study. Why this particular study? Because (spoiler alert) it suggests that FISH CAN COUNT. I don’t know about you, but I’ve always assumed that there’s not too much going on in the brain of a fish, so the results of this study really surprised me.


Xenotoca eiseni

Stancher et al. (2013) investigated whether redtail splitfin fish (Xenotoca eiseni) could discriminate between small quantities. Since redtail splitfin males compete for access to females for mating, the researchers studied whether a male could discriminate between two different quantities of females. They assumed that the male would swim toward the area of a fish tank containing the greater quantity of females.

They found that the males were able to discriminate between 1 and 2 females, and 2 and 3 females, but not 3 and 4 females. First of all, these results show that FISH CAN COUNT. Which is incredible, and suggests that some sort of counting ability developed really, really early in evolution.

Second, this pattern of results matches what we see in infants, where the number-specific system only works for quantities less than 4. However, unlike human infants, the fish were able to discriminate between 1 and 4 females, and between 2 and 4 females.

The fact that the fish were able to discriminate across the so-called small quantity – large quantity boundary indicates that they may use only one number system, rather than two independent number systems. The researchers suggest that the fish possibly use a ratio-based number system for all quantities, not just larger ones. This is supported by the fact that the fish were unable to discriminate between the quantities with the smallest ratio (3 vs. 4).

*A note about the two number systems described above: the actual terms used for these systems are the Object File System (what I called the “number-specific system”) and the Analog Magnitude System (what I called the “ratio-based system”). These terms are based on the theories of how these systems actually operate in the brain, which I didn’t have the space to detail here.


Feigenson, Lisa, Susan Carey, and Marc Hauser. “The representations underlying infants’ choice of more: Object files versus analog magnitudes.” Psychological Science 13.2 (2002): 150-156.
Stancher, Gionata, et al. “Discrimination of small quantities by fish (redtail splitfin, Xenotoca eiseni).” Animal cognition 16.2 (2013): 307-312.

Beast of Burden

Let’s talk about mules (the animal, not the shoe). The result of breeding a female horse or pony with a male donkey, mules have been used as work animals by humans for thousands of years. Why would we go through the trouble of breeding a hybrid animal (and one that is usually infertile, to boot)? Because mules have something called “hybrid vigor” — they possess the best features of both parents. For example, they have the size of a horse with the surefootedness of a donkey. Mules even exceed the physical capabilities of either of their parents; they have more endurance and can carry more weight than horses or donkeys.


It’s just simple math, really.

All of which begs the question (at least to cognitive scientists), does the hybrid vigor of mules extend to their cognitive abilities?

In order to answer this question, we’ll have to look at studies that test the cognitive abilities of mules, as well as their parent animals (horses and donkeys). If the mules perform better at a particular task than either the horses or donkeys, then we can say that their hybrid vigor includes cognition.

One such study (Proops et al. 2009) looked at the learning abilities of equines (members of the genus equus, in this case mules, donkeys, and ponies). The equines were essentially given a scaled-up version of the food-finding task given to dogs. A piece of carrot was placed in one of two barrels. Instead of having a person point to where the food was located, a picture was placed in front of each barrel. The same picture was always placed in front of the barrel where the food was hidden (the “positive” picture), and a different picture was always placed in front of the empty barrel (the “negative” picture).

Screen Shot 2013-10-09 at 2.59.29 PM

Picture pairs used by Proops et al. (2009). [Originally used by Voith (1975).]

Researchers wanted to see how long it would take the equines to learn the association between the positive picture and the food “baited” barrel. “Learning”, as defined by the researchers, occurred when an equine chose the correct barrel 75% of the time. Once an equine learned the association with one set of pictures, researchers used two new pictures, with one assigned as the positive picture and one as the negative picture. All equines were tested in 25 sessions (12 trials per session), so researchers were interested in how many different picture pairs the different equid species learned in that set amount of time.

On average, the mules learned significantly more picture pairs than either the ponies or the donkeys (the ponies and donkeys were not significantly different). Moreover, as the mules learned more pairs, it took them fewer sessions to learn each new pair (it took 8.83 sessions to learn Pair 1, 7 sessions to learn Pair 2, and only 5.4 sessions to learn Pair 3). This suggests that, in addition to learning the specific picture pairs, the mules were also learning about the task more generally.

These may seem like the same thing, but they’re different in a very important way. The mules’ 75% accuracy in choosing the correct barrel tells us that they learned the association between a specific picture and food. The fact that they took fewer and fewer sessions to learn those specific associations tells us that they may have learned, for example, that the same picture always has the food behind it.

This is because if you know that the same picture always has the food behind it, you won’t waste time checking out what’s behind the other picture. Sure, if you’re given a new pair of pictures, it may take a couple trials to figure out which picture marks the food. But once you’ve found it, you won’t spend as much time going back and forth between the pictures because you know, from previous picture pairs, that the same picture always marks the food.

Cognitive scientists usually consider this ability to generalize to be a better indicator of how good an animal is at learning.

Unfortunately, not enough ponies or donkeys learned enough picture pairs to see if their learning got faster as they learned more pairs, so we can’t compare their performance to mules on that measure. However, the fact that the mules were able to learn more picture pairs than their parent species suggests that their hybrid vigor extends to their cognitive abilities!

In another experiment (Osthaus et al. 2013), mules were found to perform better on a spatial cognition task than horses and donkeys. I won’t go into detail (this post is already too long!), but I definitely recommend reading the paper on it if you’re interested — it’s pretty short and easy to understand.


So the greater variety of genes the mule gets from its parents gives it a physical and cognitive edge over either of its parent species. We see this hybrid vigor in other species, too — for example, mixed-breed dogs tend to be hardier and have fewer health problems than purebred dogs. What are some other examples of hybrid vigor? (Hint: It doesn’t only occur in the animal kingdom!)


Osthaus, Britta, et al. “Spatial cognition and perseveration by horses, donkeys and mules in a simple A-not-B detour task.” Animal cognition 16.2 (2013): 301-305.

Proops, Leanne, Faith Burden, and Britta Osthaus. “Mule cognition: a case of hybrid vigour?.” Animal cognition 12.1 (2009): 75-84.

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.