The Big Five: Their Biology

There is some evidence of a biological basis for the Big Five personality traits, in the form of evidence of brain-activity variations corresponding to variations in four of the five.

There is also some evidence that Big-Five variations are partially heritable, and there is some evidence of differences between the sexes. However, the variations also have a strong environmental component, something that suggests that we may be able to shape our personalities to some degree.

Many other species also have personality variations, and some of these variations may be very old, dating back to the common ancestors of much of the animal kingdom.

Testing Predictions From Personality Neuroscience: Brain Structure and the Big Five

We used a new theory of the biological basis of the Big Five personality traits to generate hypotheses about the association of each trait with the volume of different brain regions. Controlling for age, sex, and whole-brain volume, results from structural magnetic resonance imaging of 116 healthy adults supported our hypotheses for four of the five traits: Extraversion, Neuroticism, Agreeableness, and Conscientiousness. Extraversion covaried with volume of medial orbitofrontal cortex, a brain region involved in processing reward information. Neuroticism covaried with volume of brain regions associated with threat, punishment, and negative affect. Agreeableness covaried with volume in regions that process information about the intentions and mental states of other individuals. Conscientiousness covaried with volume in lateral prefrontal cortex, a region involved in planning and the voluntary control of behavior. These findings support our biologically based, explanatory model of the Big Five and demonstrate the potential of personality neuroscience (i.e., the systematic study of individual differences in personality using neuroscience methods) as a discipline.

Though this work has gotten some criticism: How Not to Do Personality Neuroscience: Brain Structure and The Big Five | Psychology TodayBiological basis of personality (Wikipedia) has more on such work.

Also, Heritability of the Big Five Personality Dimensions and Their Facets: A Twin Study – Jang – 1996 – Journal of Personality – Wiley Online Library

ABSTRACT The genetic and environmental etiology of the five-factor model of personality as measured by the revised NEO Personality Inventory (NEO-PI-R) was assessed using 123 pairs of identical twins and 127 pairs of fraternal twins. Broad genetic influence on the five dimensions of Neuroticism, Extraversion, Openness, Agreeableness, and Conscientiousness was estimated at 41%, 53%, 61%, 41%, and 44%, respectively. The facet scales also showed substantial heritability, although for several facets the genetic influence was largely nonadditive. The influence of the environment was consistent across all dimensions and facets. Shared environmental influences accounted for a negligible proportion of the variance in most scales, whereas nonshared environmental influences accounted for the majority of the environmental variance in all scales.

So personality is much like IQ: partially heritable, partially environmental. For IQ, most of the variation seems to be within-group rather than between-group (the Eyferth study (Wikipedia), for instance), and that may also be the case for personality variations. There is a very odd result that also suggests a mix of hereditary and environmental factors: Why can’t a man be more like a woman? Sex differences in Big Five personality traits across 55 cultures.

(Correction Notice: An erratum for this article was reported in Vol 96(1) of Journal of Personality and Social Psychology (see record 2008-18683-004). Some of the sample sizes presented in Table 1 were incorrectly reported. The correct sample sizes are presented in the erratum.] Previous research suggested that sex differences in personality traits are larger in prosperous, healthy, and egalitarian cultures in which women have more opportunities equal with those of men. In this article, the authors report cross-cultural findings in which this unintuitive result was replicated across samples from 55 nations (N = 17,637). On responses to the Big Five Inventory, women reported higher levels of neuroticism, extraversion, agreeableness, and conscientiousness than did men across most nations. These findings converge with previous studies in which different Big Five measures and more limited samples of nations were used. Overall, higher levels of human development–including long and healthy life, equal access to knowledge and education, and economic wealth–were the main nation-level predictors of larger sex differences in personality. Changes in men’s personality traits appeared to be the primary cause of sex difference variation across cultures. It is proposed that heightened levels of sexual dimorphism result from personality traits of men and women being less constrained and more able to naturally diverge in developed nations. In less fortunate social and economic conditions, innate personality differences between men and women may be attenuated. (PsycINFO Database Record (c) 2016 APA, all rights reserved)

This abstract did not state how large the variations were, and how they compare to variations in each of the sexes.

This suggests that personality variations occur elsewhere in the animal kingdom, and there is a large volume of anecdotal evidence of personality variations in domestic animals. This is supported by systematic studies done on a variety of species (Personality in animals (Wikipedia)Personality Dimensions in Nonhuman Animals with a copy at gosling.qxd – CDPS99Xspeciesreview.pdf)).

The evolutionary continuity between humans and other animals suggests that some dimensions of personality may be common across a wide range of species. Unfortunately, there is no unified body of research on animal personality; studies are dispersed across multiple disciplines and diverse journals. To review 19 studies of personality factors in 12 nonhuman species, we used the human Five-Factor Model plus Dominance and Activity as a preliminary framework. Extraversion, Neuroticism, and Agreeableness showed the strongest cross- species generality, followed by Openness; a separate Conscientiousness dimension appeared only in chimpanzees, humans’ closest relatives. Cross-species evidence was modest for a separate Dominance dimension but scant for Activity. The comparative approach taken here offers a fresh perspective on human personality and should facilitate hypothesis-driven research on the social and biological bases of personality.

The article starts with

In a recent article in the Los Angeles Times, Robert Fagen, a professor of biometry, described Susie as irascible, irritable, grumpy, and manipulative. This is hardly newsworthy, except that Susie is a bear.

I’ve also found Is personality unique to humans? – BBC News, another discussion of research into animal personalities.

So far, evidence of personality variation has been found in chimps, gorillas, rhesus monkeys, vervet monkeys, dogs, cats, mink, horses, donkeys, pigs, camels, fallow deer, bighorn sheep, domestic bovines, bottlenose dolphins, killer whales, rats, other rodents, great tits, zebra finches, albatrosses, parrots, iguanas, other lizards, turtles, frogs, salamanders, goldfish, guppies, cat sharks, lemon sharks, other fish, honeybees, hermit crabs, colonial spiders, octopuses, and some in sea anemones.

This covers all of Bilateria, the bilaterally symmetric animals, except for certain rather obscure worms called Acoela. So how much is inherited and how much independently invented? Some personality features are correlated with neurotransmitters like dopamine, and dopamine is shared across Bilateria. Since the widest-distributed personality features are elements of Extroversion and Neuroticism, these may well be ancestral. Agreeableness and Openness are less widely distributed, and Conscientiousness has only been found in chimps, our closest living nonhuman relatives.

The ancestral bilaterian was likely a tiny worm that lived in the ocean-floor mud back in the late Proterozoic. The present-day marine worm Platynereis dumerilii is much like that inferred organism. So how do you give a worm a personality test?

Finally, an interesting bit of variation between the sexes. Neuroticism in both our species and in hyenas.

  • Human
    • Female: +0.15
    • Male: -0.1
  • Hyena
    • Female: -0.5
    • Male: +0.7

Male hyenas are much more “high-strung, fearful, and nervous” than female ones. That’s likely because hyenas have strongly female-dominated societies. Though in our species, the difference in Neuroticism is consistent with male dominance, that difference is not very great, at least by hyena standards. But this is not to say that it is all genetic. It could be at least partially a result of social environment — in both species.

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