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Personality in animals, and the closely related concept of temperament in animals, is the expression of individual behavioral traits that are stable over time and context. Other related terms include "coping styles", and "behavioral syndromes". These traits are measurable and are described in over 100 species including salamanders, fish, lizards, birds, rodents, mink, bighorn sheep, horses and cattle. Research on animal personality variation has been burgeoning since the mid 1990s. Recent studies have focused on its proximate causation and its ecological and evolutionary significance.
Contents
- Background
- Methods
- Heritability
- Relationship to other behaviors
- Five Factor Model
- In animals
- Examples
- Criticism
- References
It is important to note that the personality of an animal is observed in its consistency of an individuals behavior differing from other animals of the same species. There are also personality norms through the species, often found between genders. The diversity of animal personality can be compared in cross-species studies in order to demonstrate how pervasive it has been to the evolutionary prosses of animals. Cross-species studies can also provide evidence for the historical genetic similarities of species.
Background
There is a long history of scientists attributing personality to animals. The Russian physiologist, Ivan Pavlov, categorized dogs in his seminal studies on their behavior 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 of the four types and displayed rapid associative learning. Pavlov’s Quiet type exhibited consistent but slow learning.
There have been a number of published articles outlining the methods of measuring animal personality. There have been a number of studies done that have faced the problems of any young field of study. Samuel Gosling notes that simply because a personality trait isn't readily measurable doesn't mean it doesn't exist. He stresses that when an element of personality appears to be missing from a species, a multitude of various methods should be utilized to prove that it is not present. Gosling has developed an early map of animal personality outlining the five factor personalities and the dimensions the species exhibits. Extraversion, Neuroticism, and Agreeableness are prevalent in most of the species that have been studied for personality. Openness isn't as prevalent because it is present in about half of the species studied (this may be due to the studies methodologies not explicitly looking for openness). Opposite sexes may also exhibit different patterns of personality. For example, in humans, women score higher in worrying (a diminution of neuroticism) than do men. In hyaenas, the reverse is true, and males exhibit more neuroticism than females, because they are consistently more high-strung and nervous. Gosling states that the possibility of gender specific personalities should not be ruled out for other species. These findings have provided a cornerstone for future research to build upon.
Methods
Most empirical studies of animal personality have relied on two methods, i.e. coding of animal scores in standardized tests, and subjective rankings of personality traits by human observers. A third method, "naturalistic observations" of behavior, is based on observations of non-manipulated animals in the field or in semi-natural settings.
Heritability
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. Heritability estimates for personality traits range from 0.0 to 0.4 in a number of species in a variety of taxa, including squid, fish, birds, sheep and squirrels. In apes, including humans, heritability estimates of personality dimensions range from 0.07 to 0.63.
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.
Relationship to other behaviors
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.
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.
Five Factor Model
The Five Factor Model, or The Big Five Personalities can be used to assign personality archetypes to most animals . The 5 categories for the five factor model for personality are Openness to experience, Conscientiousness, Extraversion, Agreeableness, and Neuroticism. Each of these categories identifies a fraction of a beings personality. Because the assessment of personality using the five factor model for personalities 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 that exhibits conscientiousness.
In animals
Animals exhibiting personality factors have been categorized using the big five personalities. Neuroticism, agreeableness and extraversion are the most common personality traits among animals. For example, chimpanzees show emotional stability, agreeableness and surgency, audiovisual reactivity, affect-extraversion, excitability-agitation, aggression affinity and social play.
Examples
The spider Anelosimus studiosus 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.
Criticism
Because 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.