Personality in animals

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Many animals express individual behavioral traits that are stable over time and context Young male chimp.png
Many animals express individual behavioral traits that are stable over time and context

Personality in animals has been investigated across a variety of different scientific fields including agricultural science, animal behaviour, anthropology, psychology, veterinary medicine, and zoology. [1] Thus, the definition for animal personality may vary according to the context and scope of study. However, there is recent consensus in the literature for a broad definition that describes animal personality as individual differences in behaviour that are consistent across time and ecological context. [2] Here, consistency refers to the repeatability of behavioural differences between individuals and not a trait that presents itself the same way in varying environments. [3] [4]

Contents

Animal personality traits are measurable and are described in over 100 species. [5] Personality in animals has also been referred to as animal disposition, coping style, and temperament. [1] There are also personality norms through the species, often found between genders. [6] The diversity of animal personality can be compared in cross-species studies, demonstrating its pervasiveness in the evolutionary process of animals. [1] Research on animal personality variation has been burgeoning since the mid 1990s. [7] Recent studies have focused on its proximate causation and the ecological and evolutionary significance of personality in animals. [4]

Animal personality vs. human personality

The extent of personality phenomena considered when examining animal personality is significantly reduced compared to those studied in humans. Concepts such as personal objects, identity, attitudes and life stories are not considered relevant in animals. Similarly, any approach that requires the subject to explain motives, beliefs or feelings is not applicable to the study of animal behaviour. [1]

The study of animal personality is largely based on the observation and investigation of behavioural traits. In an ecological context, traits or ‘characters’ are attributes of an organism that are shared by members of a species. Traits can be shared by all or only a portion of individuals in a population. For example, studies in animal personality often examine traits such as aggressiveness, avoidance of novelty, boldness, exploration and sociality. [3]

Background

The initial framework used to study animal personality was comparative psychology. The descriptive language used by comparative psychologists in the late nineteenth century often attributed disposition and behavioural tendencies to individual animals in their studies. Many of these reports are the result of researchers anthropomorphizing the animal subjects and did not explicitly examine what is now considered animal personality. However, these studies do represent some of the first instances of scientists reporting individual differences in animal behaviour. [8]

Russian physiologist Ivan Pavlov was one of the first researchers to integrate personality into his research of animal behaviour. In his seminal studies on conditional reflexes, he categorized the behaviour of dogs as Excitable, Lively, Quiet or Inhibited. He linked these personalities to learning ability. The Excitable type, for example, showed signs of strong excitatory conditioning, but a limited ability for the acquisition of inhibitory connections. The Lively type was the most balanced and displayed rapid associative learning, while the Quiet type exhibited consistent but slow learning. [9]

The first study that empirically examined animal personality was done in 1938. Meredith Crawford quantified individual differences in the behaviour of young chimpanzees using a behaviour rating scale. Crawford conducted his research out of the Yale Laboratories of Primate Biology. [8] Since then, psychologists have continued to investigate personality in animals across a wide range of taxa. Meanwhile, the incorporation of animal personality into the fields of ecology and evolution is a relatively new practice. Ecologists began to recognize the importance of individual differences in behaviour near the end of the twentieth century. [10] [3]

Methods

Rating of traits

Rating traits involve a group of observers that scrutinize the behavioural traits of an individual animal. Observers are typically given a list of characters and/or descriptions to use as a reference for interpreting animal behaviour then use the list to rate the behaviours. [11] The rating method uses observers and data recording instruments. [1]

Coding behaviours

Researchers will observe how individual animals respond to behavioural tests and code their reactions. This method is typically used in experimental studies in which environmental conditions are heavily manipulated. [1]

Behavioural reaction norms

As research in animal personality became more prevalent in ecological studies many behavioural ecologists were substituting behavioural plasticity for animal personality. [10] That is, attributing variation in behaviour to diverse personality types rather than plasticity in a single behavioural trait. Thus, behavioural reaction norms were introduced as a means of incorporating personality and individual plasticity in the study of animal behaviour. Behavioural reaction norms measure the behaviour of an individual over an environmental gradient, therefore providing information on how an animal behaves on average and how their behaviour changes across an environmental gradient. [12]

Repeatability

Repeatability refers to the fraction of variation in a population that is owed to differences between individuals. Repeatability estimates are one of the most widely used statistical tools that can quantify consistent individual differences in behaviour. [13] Formally,

where, is variance among individuals and is the variance within individuals over time. [14] In a meta-analysis of published, peer-reviewed repeatability estimates, reviewers found that, in general, approximately 35% of behavioural variation among individuals could be attributed to individual differences. [15]

Five Factor Model

The Five Factor Model , or the Big Five personality trait model, has been used to assign personality archetypes to some animals. [6] The 5 categories for the five factor model for personality are openness to experience, conscientiousness, extraversion, agreeableness, and neuroticism. Each of these categories identifies personality factors at the broadest level of abstraction. Because the assessment of personality using the five factor model is often a self-reported measure for humans, applying this model to animals can be difficult to standardize. Researchers often measure personality by assessing the behavior of the being over a period of time to establish the pattern. Naturally, some animals may not have as wide a range of personality as humans do. The species of the animal determines how the personality manifests itself. Likewise, a species may be predisposed to exhibit a category of personality more than other categories. So far, chimpanzees are the only animal shown to exhibit conscientiousness. [16] Chimpanzees are also the only non-human species shown to demonstrate a hierarchical structure of personality, with two dimensions of affect corresponding to negative and positive emotionality, and a third dimension of disinhibition (vs. constraint), which is thought to comprise a regulatory system that is known to play a role in the perception and interpretation of incoming stimuli.[ clarification needed ] [17]

Neuroticism, agreeableness and extraversion are the most commonly found personality traits among measured animals. For example, chimpanzees show emotional stability, agreeableness and surgency, [18] audiovisual reactivity, affect-extraversion, [19] excitability-agitation, aggression, affinity and social play. [20]

Correlated traits and behaviors

Some behaviors are correlated into a set of personality traits that remain constant throughout different situations and contexts. These traits are referred to as behavioral syndromes. For example, the aggressiveness-boldness syndrome refers to the correlation between an individual's aggressiveness with conspecifics and boldness in novel environments. [2]

Many correlated behaviours are species specific. For instance, a study in 2014 reported that for horses, personality (quantified using a validated questionnaire) and tolerance to pain (using a Likert scale) indicated that neuroticism is negatively related to stoicism whereas extroversion was positively related to levels of expressed lameness. This suggests that pain may be more easily identified in highly extrovert horses. [21] In zebrafish (Danio rerio), Proactive and Reactive personalities express different thermal preferences and general activity within the temperature gradient. Proactive fish (more aggressive, bold risk-takers, prone to routine formation) have a preference for higher temperature environments. Reactive fish (shy, less risk-prone, more flexible) favor medium colder temperatures. [22]

Evolutionary potential

The degree of variation in a population has been determined to influence to direction and outcome of natural selection. Most scientific research has focused on genetic and phenotypic variation or differences in resource use; however, variation in consistent behaviours (i.e. personality) also has important evolutionary consequences. For example, personality in animals can affect the way individuals interact with their environment and with each other which can affect the relative fitness of individuals. [23] Therefore, personality can influence selection. Also, behavioural traits are more dynamic which may allow an animal to adapt more quickly which, in turn, can speed up the rate of evolution. [2]

Further, natural or artificial selection cannot act on personality unless there is a mechanism for its inheritance. In rhesus macaques (Maccaca mulatta), the personality traits of Meek, Bold, Aggressive, Passive, Loner and Nervous have heritability values of 0.14 to 0.35, thus indicated that there is some genetic basis to the expression of personality traits in animals. In apes, including humans, heritability estimates of personality dimensions range from 0.07 to 0.63. [24] In horses, heritability estimates range mostly between h2=0.15 and h2=0.40 for traits assessed in personality tests. Values at this level are considered as "promising" for artificial selection. [25]

Examples

Personality in animals has been studied across a wide array of taxa. Some of these studies have investigated personality in mammals, [26] elasmobranchs, [27] reptiles, [28] fish [29] and birds. [30]

Zebrafish in Fish Laboratory, Weizmann Institute. Fish Laboratory in Weizmann Institute IMG 8832.JPG
Zebrafish in Fish Laboratory, Weizmann Institute.

There have been several studies that have either been notable in that they have changed scientific understandings of animal personality or have applications in the field of human personality. For example, the study of personality in chimpanzees by King and Figueredo in 1997 [31] was one of the first studies to apply the five-factor model in animal personality. It demonstrated the existence of personality traits in animals and provided a foundation for similar assessment strategies in future studies of personality in animals. [8] Similarly, zebrafish have been used as a neurobehavioral model species for studying personality using the trait approach in non-human animals. These studies can then be translated to study personality development and personality disorders in humans. [32]

Another general example is the spider Anelosimus studiosus. This spider forms groups in which some females show an aggressive personality type and engage more in colony defense and prey capture, while others are docile and engage more in brood care. Groups containing both these two different personalities have better fitness than groups of only one personality type. This is because aggressive females are more efficient at foraging, web construction and defense, while docile females are better at raising the young. When groups contain a mix of both personalities, overall group performance is improved benefiting all group members. [33] In the social spider Stegodyphus dumicola individuals differ in their boldness, with bolder individuals having a greater risk appetite. Boldness changes were found to relate to social interactions with nest mates, indicating that individual personality is more plastic in groups. [34]

Criticism

Many researchers are critical of the lack of consistency in the terminology surrounding animal personality. For example, temperament, behavioral syndrome, disposition and animal personality have been used interchangeably by some while others maintain that each term has a unique meaning. [3] Additionally, there is some concern that researchers may be misinterpreting the relationship between personality and behavioural plasticity. Behavioural ecologist Niels Dingemanse illustrates that one could erroneously determine that variation in behaviour between individuals exists if the subjects have not been examined across a gradient of ecological contexts, and urges fellow researchers to apply behavioural reaction norms whenever possible. [12] In addition, because of critical anthropomorphism, ethology, and comparative psychology are relatively unknown concepts to the layman, there are critics that question the validity in the claim that animals have a personality schema. There are those that fear that, while assessing behaviors, researchers will project anthropomorphic ratings onto the animals. [16]

Related Research Articles

<span class="mw-page-title-main">Chimpanzee</span> Great ape native to the forest and savannah of tropical Africa

The chimpanzee, also known as simply the chimp, is a species of great ape native to the forests and savannahs of tropical Africa. It has four confirmed subspecies and a fifth proposed one. When its close relative the bonobo was more commonly known as the pygmy chimpanzee, this species was often called the common chimpanzee or the robust chimpanzee. The chimpanzee and the bonobo are the only species in the genus Pan. Evidence from fossils and DNA sequencing shows that Pan is a sister taxon to the human lineage and is humans' closest living relative. The chimpanzee is covered in coarse black hair, but has a bare face, fingers, toes, palms of the hands, and soles of the feet. It is larger and more robust than the bonobo, weighing 40–70 kg (88–154 lb) for males and 27–50 kg (60–110 lb) for females and standing 150 cm.

<span class="mw-page-title-main">Aggression</span> Social interaction aiming at inflicting harm or unpleasantness

Aggression is hostile and antagonistic behavior, often with the intent to cause harm, although it can be channeled into creative and practical outlets for some. It may occur either reactively or without provocation. In humans, aggression can be caused by various triggers. For example, built-up frustration due to blocked goals or perceived disrespect. Human aggression can be classified into direct and indirect aggression; whilst the former is characterized by physical or verbal behavior intended to cause harm to someone, the latter is characterized by behavior intended to harm the social relations of an individual or group.

<i>Pan</i> (genus) Genus of African great apes

The genus Pan consists of two extant species: the chimpanzee and the bonobo. Taxonomically, these two ape species are collectively termed panins. The two species were formerly collectively called "chimpanzees" or "chimps"; if bonobos were recognized as a separate group at all, they were referred to as "pygmy chimpanzees". Together with humans, gorillas, and orangutans they are part of the family Hominidae. Native to sub-Saharan Africa, chimpanzees and bonobos are currently both found in the Congo jungle, while only the chimpanzee is also found further north in West Africa. Both species are listed as endangered on the IUCN Red List of Threatened Species, and in 2017 the Convention on Migratory Species selected the chimpanzee for special protection.

<span class="mw-page-title-main">Handicap principle</span> Hypothesis in evolutionary biology

The handicap principle is a disputed hypothesis proposed by the Israeli biologist Amotz Zahavi in 1975. It is meant to explain how sexual selection may lead to "honest" or reliable signalling between male and female animals which have an obvious motivation to bluff or deceive each other.

<span class="mw-page-title-main">Fluctuating asymmetry</span> Form of biological asymmetry

Fluctuating asymmetry (FA), is a form of biological asymmetry, along with anti-symmetry and direction asymmetry. Fluctuating asymmetry refers to small, random deviations away from perfect bilateral symmetry. This deviation from perfection is thought to reflect the genetic and environmental pressures experienced throughout development, with greater pressures resulting in higher levels of asymmetry. Examples of FA in the human body include unequal sizes (asymmetry) of bilateral features in the face and body, such as left and right eyes, ears, wrists, breasts, testicles, and thighs.

<span class="mw-page-title-main">Richard Wrangham</span> British anthropologist and primatologist

Richard Walter Wrangham is an English anthropologist and primatologist; he is Professor of Biological Anthropology at Harvard University. His research and writing have involved ape behavior, human evolution, violence, and cooking.

<span class="mw-page-title-main">Phenotypic plasticity</span> Trait change of an organism in response to environmental variation

Phenotypic plasticity refers to some of the changes in an organism's behavior, morphology and physiology in response to a unique environment. Fundamental to the way in which organisms cope with environmental variation, phenotypic plasticity encompasses all types of environmentally induced changes that may or may not be permanent throughout an individual's lifespan.

Evolutionary developmental psychology (EDP) is a research paradigm that applies the basic principles of evolution by natural selection, to understand the development of human behavior and cognition. It involves the study of both the genetic and environmental mechanisms that underlie the development of social and cognitive competencies, as well as the epigenetic processes that adapt these competencies to local conditions.

Personality development encompasses the dynamic construction and deconstruction of integrative characteristics that distinguish an individual in terms of interpersonal behavioral traits. Personality development is ever-changing and subject to contextual factors and life-altering experiences. Personality development is also dimensional in description and subjective in nature. That is, personality development can be seen as a continuum varying in degrees of intensity and change. It is subjective in nature because its conceptualization is rooted in social norms of expected behavior, self-expression, and personal growth. The dominant viewpoint in personality psychology indicates that personality emerges early and continues to develop across one's lifespan. Adult personality traits are believed to have a basis in infant temperament, meaning that individual differences in disposition and behavior appear early in life, potentially before language of conscious self-representation develop. The Five Factor Model of personality maps onto the dimensions of childhood temperament. This suggests that individual differences in levels of the corresponding personality traits are present from young ages.

Animal culture can be defined as the ability of non-human animals to learn and transmit behaviors through processes of social or cultural learning. Culture is increasingly seen as a process, involving the social transmittance of behavior among peers and between generations. It can involve the transmission of novel behaviors or regional variations that are independent of genetic or ecological factors.

<span class="mw-page-title-main">Dog behavior</span> Internally coordinated responses of dogs to internal and external stimuli

Dog behavior is the internally coordinated responses of individuals or groups of domestic dogs to internal and external stimuli. It has been shaped by millennia of contact with humans and their lifestyles. As a result of this physical and social evolution, dogs have acquired the ability to understand and communicate with humans. Behavioral scientists have uncovered a wide range of social-cognitive abilities in domestic dogs.

<span class="mw-page-title-main">Mate choice</span> One of the primary mechanisms under which evolution can occur

Mate choice is one of the primary mechanisms under which evolution can occur. It is characterized by a "selective response by animals to particular stimuli" which can be observed as behavior. In other words, before an animal engages with a potential mate, they first evaluate various aspects of that mate which are indicative of quality—such as the resources or phenotypes they have—and evaluate whether or not those particular trait(s) are somehow beneficial to them. The evaluation will then incur a response of some sort.

<span class="mw-page-title-main">Evolutionary physiology</span> Study of changes in physiological characteristics

Evolutionary physiology is the study of the biological evolution of physiological structures and processes; that is, the manner in which the functional characteristics of individuals in a population of organisms have responded to natural selection across multiple generations during the history of the population. It is a sub-discipline of both physiology and evolutionary biology. Practitioners in the field come from a variety of backgrounds, including physiology, evolutionary biology, ecology, and genetics.

Sexual selection in humans concerns the concept of sexual selection, introduced by Charles Darwin as an element of his theory of natural selection, as it affects humans. Sexual selection is a biological way one sex chooses a mate for the best reproductive success. Most compete with others of the same sex for the best mate to contribute their genome for future generations. This has shaped human evolution for many years, but reasons why humans choose their mates are not fully understood. Sexual selection is quite different in non-human animals than humans as they feel more of the evolutionary pressures to reproduce and can easily reject a mate. The role of sexual selection in human evolution has not been firmly established although neoteny has been cited as being caused by human sexual selection. It has been suggested that sexual selection played a part in the evolution of the anatomically modern human brain, i.e. the structures responsible for social intelligence underwent positive selection as a sexual ornamentation to be used in courtship rather than for survival itself, and that it has developed in ways outlined by Ronald Fisher in the Fisherian runaway model. Fisher also stated that the development of sexual selection was "more favourable" in humans.

Behavioural genetics, also referred to as behaviour genetics, is a field of scientific research that uses genetic methods to investigate the nature and origins of individual differences in behaviour. While the name "behavioural genetics" connotes a focus on genetic influences, the field broadly investigates the extent to which genetic and environmental factors influence individual differences, and the development of research designs that can remove the confounding of genes and environment. Behavioural genetics was founded as a scientific discipline by Francis Galton in the late 19th century, only to be discredited through association with eugenics movements before and during World War II. In the latter half of the 20th century, the field saw renewed prominence with research on inheritance of behaviour and mental illness in humans, as well as research on genetically informative model organisms through selective breeding and crosses. In the late 20th and early 21st centuries, technological advances in molecular genetics made it possible to measure and modify the genome directly. This led to major advances in model organism research and in human studies, leading to new scientific discoveries.

A behaviour mutation is a genetic mutation that alters genes that control the way in which an organism behaves, causing their behavioural patterns to change.

The biological basis of personality it is the collection of brain systems and mechanisms that underlie human personality. Human neurobiology, especially as it relates to complex traits and behaviors, is not well understood, but research into the neuroanatomical and functional underpinnings of personality are an active field of research. Animal models of behavior, molecular biology, and brain imaging techniques have provided some insight into human personality, especially trait theories.

In behavioral ecology, a behavioral syndrome is a correlated suite of behavioral traits, often measured across multiple contexts. The suite of traits that are correlated at the population or species level is considered the behavioral syndrome, while the phenotype of the behavioral syndrome an individual shows is their behavioral type. For example, a population may show a behavioral syndrome that includes a positive correlation between foraging behavior and mating behavior. An individual may be more or less aggressive than another individual within this behavioral syndrome, and this aggressive or passive phenotype is that individual's behavioral type.

Behavioral plasticity refers to a change in an organism's behavior that results from exposure to stimuli, such as changing environmental conditions. Behavior can change more rapidly in response to changes in internal or external stimuli than is the case for most morphological traits and many physiological traits. As a result, when organisms are confronted by new conditions, behavioral changes often occur in advance of physiological or morphological changes. For instance, larval amphibians changed their antipredator behavior within an hour after a change in cues from predators, but morphological changes in body and tail shape in response to the same cues required a week to complete.

<span class="mw-page-title-main">Domestication syndrome</span> Proposed biological phenomenon

Domestication syndrome refers to two sets of phenotypic traits that are common to either domesticated animals, or domesticated plants. These traits were identified by Charles Darwin in The Variation of Animals and Plants Under Domestication.

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  34. ↑ Hunt, ER.; et al. (2018). "Social interactions shape individual and collective personality in social spiders". Proceedings of the Royal Society B. 285 (1886): 20181366. doi:10.1098/rspb.2018.1366. PMC   6158534 . PMID   30185649.
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