Animal personalities

Do other animals have personalities? Any pet owner would tell you: “Obviously yes, my floofy is so charismatic, no other floofy is the same.” We all think it. But since we can’t give animals a link to a “which Hogwarts house do you belong in” quiz and see how they measure up, how do we know that animals truly exhibit personalities? And what is a personality anyway?

What is a personality?

Our ideas about personalities come primarily from psychology, with the American Psychological Association defining personality as “individual differences in characteristic patterns of thinking, feeling and behaving”. Personality is thus intimately linked with behaviour; we are certain that each person (and each animal for that matter) is unique, and that we all have different behavioural quirks that persist throughout our lifetime.

Although the concept of personality includes behaviour, emotion and cognition, for the purpose of our question I will focus more heavily on the behavioural component, as it is the aspect that is most broadly comparable to other animals (being much easier to measure!). Furthermore, I operate under the assumption that differences in emotion and cognition among individuals can also be measured through differences in behaviour (to a certain extent). For example, if you are feeling frustrated by something, it is likely to show in your behaviour.

For humans, personality is considered to be a sociocultural construct; that is, it represents the elements of individual behaviour that develop through social and cultural experiences, in contrast to those elements that arise from biological differences. But we know that our genes and our physiology influence our behaviour, and animals are no different – after all, every animal has a unique combination of genes in their DNA that are likely to influence how they behave in a way that might distinguish them from others (unless they’re a clone, or an identical twin). Over time, even identical twins will be exposed to different things in their environment that are likely to influence their future behavioural patterns, particularly in species that are capable of learning.

To a biologist, this variation in individual behaviour is not surprising. One of the basic components of Charles Darwin’s theory of evolution by natural selection is variation – if organisms didn’t naturally vary in how they approach the world around them, no one organism would reproduce more or less than any other and the population would change only by chance. We know from experimental evidence that populations change much more than would be expected due to chance alone, with each generation. We also know that individual differences in behaviour contribute to this change through how they increase or decrease an organism’s reproductive success.

So one of the basic aspects of personality – individual differences in behaviour – is important for understanding the evolution of humans and other animals. However, if personality is simply the uniqueness of an individual’s behavioural patterns (which presumably are influenced by thoughts and feelings), why not just call this variation and be done with it? In reality, the definition of personality being unique to each individual is not a very useful concept without knowing what causes such variation among individuals. So how can we make this concept more useful to us? In some ways we have done this already, by expanding the concept of personality to describe different categories that people fit into; these categories are referred to as personality types.


Personality types

Although generally we talk about personalities as representations of the uniqueness of individuals, we also talk about one or more individuals having similar personalities, or individuals having a particular personality type. Early ideas about personality types grew out of classical theories on how our bodies worked and how that influenced our behaviour. These ideas gained ground in ancient Greece and Rome when physicians believed that there were four distinct types of body fluids (the four humors: black bile, yellow bile, phlegm and blood), which when unbalanced influenced a person’s temperament and health.

Obviously, we have now moved on from this humoral idea, but we do still like to talk about personalities in a categorical way. How can one concept both distinguish individuals as well as unify them into groups? The idea of personality types is partly due to our innate desire to find patterns in the world and to classify things into categories. Surprisingly, although the origins of personalities came out of physiological theory (i.e. how the body works), their later derivatives became further removed from the underlying biology. The study of personality then became an exercise in collectively describing and categorising human personality by its most basic observable components – behavioural patterns.

One of the problems with these kinds of personality classification systems is that they involve a certain loss of information along the way. In reality our behaviour is likely to vary along a scale relative to other individuals and no two individuals will be exactly alike. Furthermore, an individual’s behaviour is likely to change over time along with changes in their life experience, and is likely to depend on the circumstances they find themselves in at any particular moment.

This became clear in the field of personality with the popularity of the Myers-Briggs type indicator. The Myers-Briggs is a personality test that has been widely used to inform employers about team dynamics by classifying individuals into one of 16 personality types. Although many people find these personality types useful for reflecting on their own and others’ behaviour, the personality types developed for the Myers-Briggs were not based on valid science, and most people receive a different result each time they take the test. As a result, the test has fallen out of favour among most experts.

However, finding patterns in behaviour across groups of individuals has not lost its value. It allows us to better understand why individuals behave differently and to predict their future behaviour. Similarly, describing all of the possible components of a personality in such a way that they can be compared across individuals also allows further understanding of why people differ as it allows a standardised measure of such differences. These two ideas are reflected in a slightly different concept: personality traits. Importantly, this concept is a population measure, rather than an individual measure.

Personality traits

The most widely accepted method for measuring behavioural patterns at a population level involves a much more mathematical perspective on personalities, based on a technique called factor analysis. Factor analysis is a quantitative (i.e. measured in a numerical way rather than by description) statistical methodology that analyses all of the relationships among a set of related variables and attempts to describe them using the smallest possible number of summary variables. In this way, we can examine all of the existing variation in how different individuals behave in all sorts of situations, and organise all of this information into digestible chunks.

In other words, factor analysis is simply a way of reducing the amount of observable variation into a simpler form. This is possible because of the way that many personality characteristics tend to co-occur within individuals. So if we see that some characteristics frequently occur together, we can assume one part of a person’s personality based on another known part of their personality. Information is still lost along the way, but the additional information is subsumed by, and informs the interpretation of the broad categories that are produced.

E.g. we might observe that people who are consistently organised are less likely to also be spontaneous. If you then arranged ‘organised’ and ‘spontaneous’ at two ends of an axis, it can then represent a new variable, which might be called conscientiousness. That way, instead of having to say that someone is organised and not spontaneous, (2 bits of information), we can simply say that they show high conscientiousness (one bit of information). Lots of variation in behaviour can therefore be described in a much simpler way. Out of this approach came the recognisable ‘Big five personality traits’ and similar models such as the ‘Eysenck personality questionnaire’ and the ‘HEXACO model’. Examples of the personality traits described by these methodologies include extraversion, conscientiousness, openness, agreeableness, neuroticism, honesty-humility and psychoticism.

Similar personality traits have been described for other animals, in particular variations similar to extraversion, agreeableness and neuroticism seem to show up in other species, including primates, mammals, fish and octopuses [1]. Although this idea of personalities is still somewhat removed from the underlying biology (that is, the existence of these patterns doesn’t tell us how or why behaviour varies in this way), it now serves as a scaffold on which we can build evidence of underlying mechanisms. For example, scientists are now finding associations between brain anatomy and some of the big 5 personality traits in humans [2].

This is where our animal friends may come in handy once again. If similar latent traits can be found in other animals, then it may be possible to investigate the biological mechanisms involved and the common contexts in which certain behaviours are more or less beneficial for reproductive success [3]. Considering this, many biologists have attempted to study personalities in other animals by measuring behaviours that can be interpreted in a similar way to some of the well known components of personality in humans. In fact, scientists have already conducted similar studies on the associations between brain anatomy and personality traits in chimpanzees, for example [4]. With time, convergence of human and other animal studies is likely to lead to great discoveries in the field of personality.

  1. Gosling SD, John OP. Personality dimensions in nonhuman animals: a cross-species review. Current directions in psychological science. 1999 Jun;8(3):69-75.
  2. DeYoung CG, Hirsh JB, Shane MS, Papademetris X, Rajeevan N, Gray JR. Testing predictions from personality neuroscience: Brain structure and the big five. Psychological science. 2010 Jun;21(6):820-8.
  3. Weiss A. Personality Traits: A View From the Animal Kingdom. Journal of Personality. 2017 Apr 1.
  4. Blatchley BJ, Hopkins WD. Subgenual cingulate cortex and personality in chimpanzees (Pan troglodytes). Cognitive, Affective, & Behavioral Neuroscience. 2010 Sep 1;10(3):414-21.


Common Critter Compendium: Pigeons

Welcome to the first in a series of snippets highlighting uncommon facts about common animals. Today: pigeons. They’re one of those iconic aspects of city life, along with skyscrapers, cars and slow people who get in your way (or should that be rude fast people who are always in a rush?). Rock pigeons (Columba livia), including domestic pigeons and feral pigeons (also known as street pigeons or city pigeons), inhabit a large proportion of the globe due to their ability to exploit human buildings for nesting sites, and human rubbish for food. Feral pigeons are descended from domestic pigeons who themselves were descended from the original wild rock pigeons found naturally in southern Europe, northern Africa and southern Asia.

Most city dwellers think of pigeons as dirty, diseased and stupid animals. I myself am guilty of calling them ratbirds on several occasions. Most of us know that pigeons have extraordinary capabilities for navigation, having been selectively bred as messenger birds, but did you know that pigeons have been used in cognitive research for over 50 years? Researchers have trained pigeons to discriminate between pictures of various classes of objects, showing evidence that the pigeons can apply what they’ve learnt to new pictures that they hadn’t seen before, even for complex and abstract objects.

In one of the first such experiments in the 1960s, pigeons were trained to peck at photos that contained humans and not to peck at photos that contained no humans [1]. The pigeons were able to do this sucessfully, including for photos that they hadn’t seen before. In the 1990s, pigeons advanced to distinguishing picasso-like paintings from monet-like paintings, like little feathered art connoisseurs [2]. The researchers involved in this behavioural research argue that this ability reflects the pigeons’ capacity to conceptualise different classes of objects, indicating that most birds and mammals are probably capable of conceptualisation.

Although it’s still unclear whether pigeons and other animals conceptualise things in exactly the same way that we do, it makes sense that animals are able to remember and respond to different categories of objects using visual cues. This ability is presumably useful for categorising things in the environment, for example things that are likely to eat you and things that are not. However, it is unclear from this research exactly which cues the pigeons use to distinguish among categories.

This makes me wonder whether animals have folk taxonomies of their own, and how they might categorise objects differently to us (if you haven’t read my post about classification systems, you can do so here). Researchers have also provided evidence for pigeons’ ability to match rotated symbols (a common task in IQ tests that humans often struggle with), and their numeracy skills, among others. So next time you pass a pigeon in the street you might just wonder what’s going on in that little brain of theirs!


  1. Herrnstein RJ, Loveland DH. Complex visual concept in the pigeon. Science. 1964 Oct 23;146(3643):549-51.
  2. Watanabe S, Sakamoto J, Wakita M. Pigeons’ discrimination of paintings by Monet and Picasso. Journal of the experimental analysis of behavior. 1995 Mar 1;63(2):165-74.

Do other animals have social rules?

We humans are very good at social rules. We have complex systems through which we encourage others to behave in a certain way, including laws, taboos, customs and many unspoken social norms. Social rules are essentially expected patterns of behaviour in a particular situation or social context, which vary across cultural groups. Often, there is some sort of social consequence for individuals who don’t behave in the expected manner. Think of the rules involved in play between two animals; the social rules of play are different to the social rules in other contexts (e.g. feeding). During play, subordinate individuals are free to jump on, chase, or bite dominant individuals without consequence – as long as they don’t bite too hard!

The existence of such context-dependent behaviour in animals requires at least two things: a) a signal denoting that any following behaviour is considered ‘play’ and is associated with different expectations, and b) a socially enforced consequence when the appropriate behaviour is not displayed in that context. So when a pretend play-bite goes too far, the play partner might retaliate with aggression, or stop playing (NB: this rule does not apply to human-cat interactions, in which case they’ll constantly cheat and you’ll inevitably fall for their innocent belly-revealing ruse over and over, because damnit, they’re just too cute!).

Most reference to social rules and social norms centres on human societies, with significant overlap in definitions of social rules, social norms, and cultural norms. There is surprisingly little literature on this topic with respect to other animals, at least in a general sense. Here, I will consider social rules as abstract concepts that dictate what an individual should do in a certain social situation or interaction. I contrast this with social or cultural norms, which are an emergent property of groups of individuals (i.e. an observed common pattern of behaviour) that can arise from the existence of social rules. I make this distinction because social/cultural norms can also arise via other mechanisms (for example, if all individuals followed the same cultural model, they may end up behaving in the same way, without an associated enforcing rule).

The evolution of social rules is intimately linked with the evolution of group living, cooperation, and common goods. This seems a pretty obvious connection; in order to have rules on how to interact with others, you need to first be likely to interact with others. However, many usually solitary species also show some form of social rules – individuals do have to interact with others occasionally, particularly for the all-important task of reproduction. Likewise, individuals all want the same food sources and will compete with other individuals to gain access to them, so even solitary foragers need to know where they can go to eat in peace. Think of the way that many animals mark territories with scents or sounds – these signals allow both the territory owner and any intruders to avoid social interaction and any potentially aggressive confrontations.

Even in solitary species then, there are usually rules for how to interact that involve signalling of a situational context, which, if not followed, result in social consequences. These consequences might simply be that the interaction ceases, that a chance at reproduction is denied, or that aggression will occur. While in humans, rules are often socially learned and socially enforced, rules of interaction in other species may be elicited and enforced in other ways, without the use of language. This includes not only visual signals and gestures, but the aforementioned olfactory (smell) and auditory (sound) signals too.

For example, in the eusocial hymenoptera (e.g. Vespula vulgaris, the common wasp), colonies consist of a queen, who builds the nest and then produces eggs, and the workers, who cooperatively forage, tend to eggs and fix and protect the nest. In these species, worker females are often able to reproduce independently, by laying unfertilised male eggs. However, when the queen has mated with multiple males, workers are more closely related to the queen’s offspring than they are to their fellow workers’ offspring. This gives workers an incentive to stop other workers reproducing. Workers have been shown to police each other’s reproduction by eating worker-laid eggs when they come across them. Generally this is achieved via olfactory signals on the eggs, but in some species egg-laying worker females also receive aggression from other workers, suggesting some social enforcement of this reproductive rule.

The problem with this very broad and abstract definition of social rules, is that other things can dictate what an individual animal does, aside from other individuals of their species. Cognitive psychologists and biologists have investigated these processes in a great deal of detail. These processes involve simple ‘rules of thumb’ or heuristics and iterative learning, such as: eat things that taste delicious, and don’t eat things that taste repulsive. This kind of behaviour does not require that anyone tells you what to eat and what not to eat, it is simply a behavioural response to a physiological stimulus, which may be learned based on previous experience with things that tasted that way in the past and had nasty consequences.

What about if an individual learns when to eat in a social context, for example, a subordinate wolf tries to eat from a cooperatively hunted kill but a dominant individual is aggressive towards them. After a few attempts the subordinate learns that they can eat in peace if they wait until after the dominant wolf has eaten. Is this an example of a social rule, then? It certainly seems to fit our abstract definition of a social rule, but how is it any different to learning how to respond to inanimate objects in response to an unpleasant stimulus (e.g. pulling your hand away when you touch a hot stove)?

Frans de Waal touched on this issue in his book, Good Natured, noting that the problem with ascribing these situations as socially enforced rules is that we are assuming intentionality on the part of the dominant individual. “We do not know if the rules that we recognise in animal behavior, and that we see being enforced, exist as rules in the animals’ heads” [1, p. 96]. It is difficult to solve this puzzle because it is hard to measure this level of intention in other animals. Social rules could therefore be said to exist in other animals, but individuals may not be consciously aware of their existence in the same way that humans are, particularly in the sense that we communicate the rules and our intentions to each other through language.

To investigate the presence of intentionality in animal social rules requires more sophisticated research beyond simple observation, since only behaviour itself is visible to us and not the intentions behind it. Evidence for this concept has been building from the philosophical and psychological field of ‘Theory of Mind’ – the ability for individuals to attribute mental states to themselves and others. Scientists have attempted to determine whether various species possess even a rudimentary version of this ability, including nonhuman primates, birds and dogs.

For example, scrub jays are known to store surplus food in caches within their territories. Some scientists argue that scrub jays show evidence of theory of mind because they will re-cache food in another location if they were observed by another jay the first time they buried it. It is argued that the jays infer that the other individual now knows where their food is and therefore that they will steal it. However, it is possible that this behaviour too can be explained by simpler behavioural rules based on past experience [2]. Other suggested evidence for intentional behaviour and theory of mind in other animals is similarly hotly debated. So far, I am not quite convinced by the available evidence, so our question about social rules in other animals remains unresolved, except that we can say on the surface many organisms do appear to follow social rules. I am certain that with time, cognitive science will move closer towards an answer on whether animals are cognitively aware of such rules or not.


  1. De Waal, F.B., 1996. Good natured (No. 87). Harvard University Press
  2. van der Vaart, E., Verbrugge, R. and Hemelrijk, C.K., 2012. Corvid re-caching without ‘theory of mind’: A model. PLoS One, 7(3), p.e32904.

Babbling bingo – babies, birds and bats

How do scientists decide how to group animals into categories? The grouping of organisms into categories in science is known as Taxonomy (for the word nerds, the term originates from the Greek taxis, meaning ‘arrangement’, and nomia, meaning ‘method’ or ‘science’). Essentially, this is a field of biology that sets the rules regarding the names of organisms and what category of organisms they fit into. A taxonomy (as a noun) can therefore tell us whether an organism should be labelled as ‘plant’ or ‘animal’, ‘fish’ or ‘fungus’ (for example). But how do we decide what each category is and what qualifies an organism to fit in that category?

Some of the earliest Western classification systems, building on the obvious animals vs. plants distinction, classified both existing and non-existing organisms by such things as usefulness and awesomeness. For example, in the Great Chain of Being (a philosophy of life that was popular during the Renaissance) wild animals were placed separately on the chain because they were so awesome that they could not be tamed, thus necessitating a separate category from the wimpy domestic animals. And useful working animals like horses were separated from other domesticated animals that were more useless in economic terms (like pets). Granted, the Great Chain of Being also encouraged the notion of “higher” and “lower” beings (in a moral sense, which is heavily value-laden and not very scientific) and it also included nonexistent organisms like angels. But in some ways the Great Chain was onto something.

Despite the drawbacks of the Great Chain of Being, the concept of classifying animals based on usefulness is actually a perfectly logical methodology. In fact, most cultures seem to have converged on similar classification systems focusing heavily on edibility and domestication, generally also with a basic distinction between plants and animals. Other categorical additions include the ways in which the organisms are obtained for food. These kinds of classification systems are called folk taxonomies. Interestingly, within these various folk systems, a single type of organism (i.e. a species) can belong to a number of different categories (i.e. the system is poly-hierarchical). This is very unlike scientific taxonomy in which each organism belongs in one place in the hierarchy, nested within larger groupings of similar organisms.

Folk classification systems are highly contextual, and differ among cultures and individuals. For example, in her study of the folk taxonomies of the Anindiyakwa people of Groote Eyelandt, Julie Anne Waddy [1] noted that “English speakers would find the folk generic taxon goanna (monitor lizard) sufficient for their purposes without further differentiation among the six or eight scientific species. But to an Aborigine each of these goanna species is a potential food source whose differences in behaviour and habitat one needs to be aware of in order to obtain a meal and therefore each one is assigned to a different folk generic taxon.” In this context, there is an important reason to have different names for each type of goanna that wouldn’t really apply if you weren’t interested in eating them.

For biological science, the development of a comprehensive classification system for all organisms stemmed from a desire to catalogue the natural “order” of the universe, to understand the similarities among all living organisms and to standardise the naming of organisms. Carl Linnaeus is widely regarded as the father of taxonomy; in his major work Systema Naturae (published in 1735), he firmly established the binomial naming system (with every organism being named in a standardised way using a latin genus and species name – still the standard method today!). In addition, Linnaeus characterised the major hierarchical groups: kingdom, class, order, genus and species, to which a few more levels have been added since (domain, phylum and subspecies among others).

The work of Linnaeus provided an excellent foundation, but it was developed before there was an understanding of evolution and genetic inheritance of traits. Before Charles Darwin’s theory of evolution by natural selection (published in 1859), and the discovery of DNA and its role in inheritance, organisms were classified based solely on similarities in visible (i.e. physical or behavioural) characteristics. This meant that the groupings of organisms were often arbitrary,especially considering that the available technology didn’t allow easy observation of subtle differences in form and function. At the time, it was assumed that similarities in the observable physical characteristics of organisms reflected a natural hierarchy of relatedness, with more similar looking organisms being more closely related. Because changes in DNA sequences affect all morphological characteristics in some way, studying the differences in physical features between organisms often achieves similar results to studying the differences in DNA.

However, some of the developments in taxonomy following the discovery of genetics and evolution have been surprising. For example, elephant shrews (pictured below) were originally thought to be most closely related to shrews (a group of mole-like small mammals), despite the recognition of their elephant-like snout (hence the common name). At face value, they do look much more like a shrew than like an elephant, but molecular evidence now suggests that elephant shrews are more closely related to elephants after all!

Nowadays, with our extensive knowledge of the way in which genes interact with environments to produce the shapes and forms of all organisms, the scientific field of taxonomy largely describes the evolutionary and genetic relationships among organisms. Essentially, most organisms are now grouped based on shared ancestry, as determined by DNA sequencing, and these ancestral relationships are displayed in the form of a branching tree. The inevitable culmination of taxonomies based on evolutionary and genetic relationships was a major step in our understanding of the living world. Grouping organisms by their evolutionary relatedness works very well if you’re trying to build a mono-hierarchical taxonomy in which each organism exists in one standard place relative to all other organisms. This system is also great for standardised naming of species.

A mono-hierarchical classification based on evolutionary relatedness works because differences in DNA and in physical features accumulate between different populations of organisms when they no longer interbreed, and the longer the populations are separated, the more differences are likely to accumulate (this is how we get new species, but that’s a story for another day). For example, imagine that two populations of a single species are suddenly separated by a body of water that they are unable to cross (as has happened many times in natural history due to changes in sea level). The two populations can no longer interbreed, and so new DNA mutations that emerge in one population will usually not be present in the other. Over time, the number of DNA changes that differ between the two populations will increase purely by chance, and if those changes affect physical or behavioural characteristics then the two populations will begin to look and act different.

However, other factors can influence the rate and degree of divergence between two populations, through the mechanism of natural selection. For example, if a major predator was on one side of the new body of water, but not on the other, one population will accumulate changes in DNA that affect the organisms’ ability to escape that predator. Perhaps the population over time becomes smaller in size and more cryptic in behaviour, because those individuals that were smaller and tended to hide were more likely to survive and reproduce, and these two traits were inherited by their offspring. Differences in the environment thus influence the degree of similarity among even closely related species that haven’t been separated for a long time.

These two concepts – the order of new species arising over time and the degree of divergence between them – are both necessary for an accurate scientific taxonomy and are now much easier to divulge due to the advancements in DNA technology. But the result is that now taxonomies only tell us about some similarities among organisms – those that are inherited from a common ancestor.

Similar characteristics arising from shared ancestry between two species are termed homologous. But some similarities among organisms arise from similar functions, or similar environments, rather than shared ancestry. These characteristics are termed analogous. This takes us back to the idea of grouping organisms for different functional purposes (i.e. can I eat this or not? Will this animal attack me or will it leave me alone? Is this a fluffy animal or a non-fluffy animal?). In addition to the more practical uses (like not getting attacked, or calculating the probability of a fluffy cuddle), thinking about groups of organisms that share behavioural or morphological characteristics (despite being distant evolutionary relatives) can be very useful for understanding why animals do the things they do.

Biologists essentially do this when studying the evolutionary origins of specific behavioural and morphological characteristics. It is particularly interesting when a similar characteristic appears in two very distantly related species, because it suggests that there is some similar environmental factor shared by those species that favours such a characteristic. This can help to build knowledge about the complex relationships between environments and the species that inhabit them. For instance, many behaviours that were once thought to be unique to humans and some of our closest relatives exist in similar forms in other, often distantly related organisms. Exploring the circumstances in which these behaviours arise in each species can tell us something about why that behaviour is useful, in humans or otherwise.

I will leave you with the example of “babbling”. Babbling is a stage in human language development in which infants imitate sounds that they have heard, and string them together into nonsensical phrases. Babbling is distinct from true language because it doesn’t convey any meaning. During development, the social feedback obtained from parents and other individuals reinforces the use of certain sounds and leads to the acquisition of meaningful language (a process known as vocal learning). Although language is still considered uniquely human, “babbling” has been observed in several other species in which individuals need to develop complex vocal repertoires. These species include many songbirds, pygmy marmosets and greater sac-winged bats. Perhaps other species will be added to the babbling bingo as we discover more about communication in other animals?

Obviously, the reason why we share this characteristic with these species is not because we all inherited it from a common ancestor. This tells us that there’s something very useful about this behaviour for animals with complex and social vocal systems, and that there is much that we can learn from our fellow babbling rellies about the purpose of this particular behaviour. There are so many more examples of this ‘convergent’ evolution, many of which are yet to be discovered.

  1. Waddy JA. Classification of plants and animals from a Groote Eylandt Aboriginal point of view. The Australian National University; 1988