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.
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.
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 . 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 .
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 . 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 . With time, convergence of human and other animal studies is likely to lead to great discoveries in the field of personality.
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- 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.
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- Blatchley BJ, Hopkins WD. Subgenual cingulate cortex and personality in chimpanzees (Pan troglodytes). Cognitive, Affective, & Behavioral Neuroscience. 2010 Sep 1;10(3):414-21.