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Silvery marmoset (Mico argentatus).
Silvery marmoset (Mico argentatus).

Why Do Researchers Wonder Whether Animals Have Personalities?

Every friend of dogs, cats, or birds knows what some researchers struggle to prove. Let’s take a look at what they found

Recently, a research team announced that marmosets — small highly social New World monkeys — display personality traits, whether they are wild or captive:

Some individuals were fast to approach any novelty, while others were more careful; hereby showing a similar pattern to humans: for instance, some humans enjoy trying out new restaurants, whereas others prefer to eat in their favorite restaurant. What is more interesting, when comparing personality traits of monkeys in Austria across four years, the authors found that these monkeys are quite consistent in their personality traits (e.g., those that are explorative when they are younger, stay similarly explorative four years afterwards).

University of Vienna, “Marmoset Monkeys Have Personalities Too” at Neuroscience News The paper is open access.

While a marmoset’s personality typically did not change, those who became dominant in family hierarchies grew bolder over time.

But, we might ask, why should anyone have been surprised? Why shouldn’t animals have personalities? They have individual bodies and individual experiences. They certainly don’t need human-like intelligence to have a personality. A working memory is probably good enough.

Another recent study allowed us to know that dogs are aware of their own bodies:

In the experiment, dogs asked by their owners to pick up an object attached to the mat they’re sitting on apparently understand that they need to move their bodies in order to complete the task.

In this study, researchers used the mat setup to test more than 50 dogs of various breeds, sexes, and ages. The team found that, like elephants and most toddlers, dogs are much more likely to get off the mat when asked to pick up an object attached to the mat than they are in any of the various control conditions. The researchers note in their paper that the study presents the first evidence of this kind of awareness in Canis familiaris.

Catherine Offord, “Dogs Pass Test for Awareness of Their Own Bodies: Study” at The Scientist The paper is open access.

Perhaps only skeptical researchers would be much surprised by this find. But, we learn, one factor is that previous research groups were relying on the “mirror test” to determine self-awareness and individuality (personality): “Dogs typically fail the well-known mirror test, for example, in which an animal is marked with pen or paint and then presented with a mirror; animals are considered to have passed that test if they investigate the mark, because it suggests they recognize their own reflection.”

But the mirror test is a flawed research idea. For one thing, it assumes that other life forms have the same distribution of sensory gifts as humans. Humans perceive the world mainly through eyes and ears but dogs learn much of what they know by their noses. As one evolutionary biologist put it, “Honestly, the test sucks.” Many researchers ertainly began to wonder when a fish, the cleaner wrasse, not known for self-awareness, passed the test. But dogs didn’t. So what are we really measuring here?

No one who works with dogs doubts that they have individual personalities and can solve problems that do not require the use of abstract reasoning. Students of canine nature at Your Dog Advisor offer us eleven different typical canine expressions with a rough translation into the human: for example, the “submissive grin,” the “hard stare/whale eye,” and the “guilty” look. Variations in the frequency of looks that convey specific emotions should be quite enough to establish personality and self-awareness.

Recent years have seen several papers exploring personality in cats as well. Contrary to what many have assumed, cats do recognize their names but they recognize them as signals, not abstractions. And, contrary to reputation, cats do bond with people. In a study published in Nature, cats showed roughly the same level of attachment to caregivers as children and dogs did. That makes sense if we consider that a domestic cat gets accustomed, as a kitten, to trusting humans to provide for him. After Mommy leaves his life, humans become his new Mommy and he expects them to help him solve problems he can’t solve for himself. And cats are very much individuals.

But what about other animals? How far can we assume that they have personality?:

Primate apes: Few researchers doubt that chimpanzees and gorillas, for example, have personality. However, efforts to try to integrate them with human life or teach them human language have not turned out well. A welcome new focus of research is the attempt to understand chimpanzees and gorillas in the context of their natural environment, rather than expecting them to be like people.

Dolphins and whales: Individual personality is generally accepted for dolphins and whales. Blake Morton at the University of Hull says, “Dolphins were a great animal for this kind of study because, like primates, dolphins are intelligent and social. We reasoned that if factors such as intelligence and gregariousness contribute to personality, then dolphins should have similar personality traits to primates.” (BBC, February 22, 2021) As for whales, “Killer whales display personality traits similar to those of humans and chimpanzees, such as playfulness, cheerfulness and affection, according to new research published by the American Psychological Association.” (American Psychological Association, Phys.org, November 15, 2018)

Unfortunately, as with chimpanzees, attempts to establish human-like relations with marine mammals have usually turned out badly for the marine mammals. Personality doesn’t mean compatibility with human demands or lifestyles.

Birds: Ravens, to take an outstanding example, can be as smart as chimpanzees but — as bird lovers know — they also have individual personalities. A bird nerd recounts the different individual personalities he has encountered among budgies. But difference in personality has also been demonstrated in song sparrows in research published in Nature.

Reptiles: With reptiles we are taking a big jump into the world of the exothermic (cold-blooded) life forms — as opposed to the endothermic (warm-blooded) ones, that is, mammals and birds. In colder environments, exothermic animals may spend a lot of time just being inert, as their body temperature falls to match their surroundings. One advantage is that they need less food. But how does their way of life affect personality?

A reptile care specialist site tells us, “While reptiles do not have the ‘typical’ personality traits of other companion animals such as dogs, cats and birds, they do have their own assortment of fascinating habits and behaviors, and during the course of your relationship with your reptile, you may even observe some signs that a human-animal bond has taken place.” The bond consists in handling the reptile while young, so it gets used to it. Emotional bonding is probably not what is happening there. A veterinarian offers a perspective, with this type of advice:

♦ Reptile species that are naturally gregarious such as leopard geckos (Eublepharus macularis) and bearded dragons (Pogona vitticeps) thrive better when kept in groups, especially when a single male is kept with multiple females.

♦ Mirrors and other reflective surfaces should be avoided in enclosures, as a reptile’s reflection may be perceived as a dominant conspecific and create undue stress or may be perceived as competition and therefore may be attacked, causing injury as the reptile strikes the surface.

♦ Keeping male reptiles in cages that allow for visualization of other males may prove to be socially stressful to them. Therefore it is best to avoid a setup in which direct visual contact can be established.

♦ The presence of other domestic pets can be perceived as threatening to captive reptiles, and attempts to minimize or eliminate visual contact are recommended.

Jörg. Mayer, Teresa Bradley. Bays, “ Reptile Behaviour ” at Veterian Key

The advice given makes clear that the reptiles discussed can have a social life and social hierarchy when they are not torpid, which implies personality of some type. And what are we to make of this type of behavior?:

Clearly, the turtle recognizes another turtle and perceives that being flipped upside down is wrong (it can be fatal). But how? We are only beginning to understand animal psychology but we can’t rule out reptile personality, however odd it may appear to us.

Fish? Even fish? As with reptiles, fish do have personalities, in the sense of individual differences in behavior: “In a study at the University of Exeter in the UK, Thomas M. Houslay and his researchers found that when Trinidadian guppies were exposed to stressful situations, they responded in different ways. Some hid, some approached cautiously after a while and some weren’t phased at all. That in and of itself, isn’t too surprising, but what’s interesting is that certain individuals responded the same way to different forms of stress, meaning their personalities didn’t change even when their circumstances did. Is that genetic, environmental, learned or something else? More research is needed.” Here’s more on the 2017 study: “The presence of predators had an effect on ‘average’ behavior — making all of the guppies more cautious overall — but individuals still retained their distinct personalities.” (Sci News, September 25, 2017) The paper is open access.

But what about invertebrates like octopuses and insects? What about one-celled animals and plants? That’s coming up next.

Note: The image of the common marmoset is courtesy Vedrana Šlipogor.

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Denyse O'Leary

Denyse O'Leary is a freelance journalist based in Victoria, Canada. Specializing in faith and science issues, she is co-author, with neuroscientist Mario Beauregard, of The Spiritual Brain: A Neuroscientist's Case for the Existence of the Soul; and with neurosurgeon Michael Egnor of the forthcoming The Human Soul: What Neuroscience Shows Us about the Brain, the Mind, and the Difference Between the Two (Worthy, 2025). She received her degree in honors English language and literature.

Why Do Researchers Wonder Whether Animals Have Personalities?