A friend of mine is commonly described as “out-going.” She loves to travel, explore culture, socialise and can sometimes be promiscuous with the men. She also has a myriad of interests that are continually changing in their hierarchy of importance. For instance, she was once eager to pursue a career as a police officer, only to later change her mind, opting to go to university in order to become a paramedic. She plays for a football team, has been a bar maid, an estate agent – has travelled, lived and worked in several different countries– and is on her way to acquiring a degree. She’s done all of this and she is not yet even 25 years old. Psychologists would label her personality as overwhelmingly extraverted.
Extraverts, in general, will spend more time schmoosing at social events, are more ambitious and can be warm blooded when it comes to competition, enjoy travelling as well as sexual divergence and will desire the spotlight. We all know such people and are all, to some degree, beholden to the same traits in ourselves, just to less of an extreme in comparison to people such as my friend. Why has such a prolificate personality persisted through the drudges and hardships of evolution; what advantages does it yield and what are some of the costs that must be paid for having such a personality?
Personality is largely heritable, meaning, when psychometricians record variance in the population for the degree of extroversion, 50-to-70 per cent of that variance is accounted for by differences in the populations genetic profile. Genetic polymorphisms (changes to, but maintenance of, functional genes) and their expression in neurobiology, particularly, in the dopamine and serotonin systems, appear to be related to one’s phenotypic expression of extroversion. This infers that at some point in ancestral time, such a personality trait, and its corresponding genes, must’ve been selected for in some way.
The evolutionary process of natural selection generally has the effect of getting to the best genotype, pruning out any polymorphism or variation, that can interact successfully with the environment. Yet, the discovery of persistent polymorphisms for genes that code for dopamine receptors and proteins that carry serotonin back from the synapse, both of which have implications for social behaviour, suggests that natural selection has not winnowed out all polymorphic variation. Slight genetic divergence, important for expressed extraversion, in fact, has endured the pressures of natural selection!
Thus, despite the eliminatory effects of natural selection, the trait extraversion has displayed heritable variation among the population. This renders a question: why has such variation persisted and why has natural selection not extracted one genotype that fits-all?
Firstly, just as natural selection removes polymorphisms that are abhorrent, or not optimal, to one’s survival, mutation produces them. If, then, the rate of mutation is greater than the winnowing powers of natural selection, a variance of polymorphisms could continue to persist. Suppose a trait, like extraversion, is affected by an abundance of genetic targets; this would expand the number of targets that could become mutated, as well as create a greater workload for selection processes; creating an imbalanced rate of selection pruning and mutation – favouring the degree to which someone expresses, or does not express, a trait such as extraversion.
Secondly, the optimal expression of extraversion maybe different for varying subsets of the environment. In addition, the environment changes overtime, and these changes may favour certain levels of trait expression at different times. These environmental dynamics could produce such a varied trait optimal landscape, whereby one subset of the environment, compared to another, maybe more adherent to an extraverted personality. For instance, an environment that lacks plentiful resources may better serve a person who seeks novelty and doesn’t mind competing for resources or status– traits consistent with extraversion; whereas, an environment that is bountiful, perhaps, would serve someone who is less prone to risk or novelty-seeking, tending to rather consolidate their already held resources and societal position.
Clearly, these two opposed environments fluctuate in how conducive they would be to extraverts and, therefore, would determine how likely the corresponding polymorphisms, coding for extraversion, would be to persist in a population. Additionally, these two comparably divergent environments my not be mutually exclusive, which creates a difficulty for natural selection: as the process cannot track the most optimal genotype for the two changing, and at the same time coexisting, environments.
Lastly, the persistent variation seen in how extraverted one person is to another is conceivably due to how widely the trait is dispersed, or how frequently it’s expressed, within a population. If a trait, such as extraversion, attains “fitness” (i.e. reproductive success through mate selection) for a carrying phenotype and is also rare in a population, it has the potential to spread rapidly. Once the polymorphisms corresponding to extraversion have more widely spread throughout the population, the extraverted personality phenotype will either attain a greater level of fitness, benefiting from a wider variety of extraverted people, or the traits’ benefits will become quickly void of all previous potency – the trait has been defeated by its own success.
The variability as well as persistence of extraversion among us suggests that, indeed, the trait has revelled in its spreading success and enjoys having compatriots to be extraverted with. However, what benefits did being extraverted bring for the trait to be spread so widely during its initial origin, and how does being extraverted aid a person’s evolutionary fitness now?
Daniel Nettle, an evolutionary psychologist at the University of Newcastle, has tested such hypothesises. Nettle’s studies contend that equated with introverts, extraverts (such as my friend from the opening paragraph) contribute more of their time to the social arena, are prone to a will of ambition, are competitive and are merry when traveling to subjectively novel places. The pursuit and enjoyment of sex, apparently, is not lost on the extravert, as the higher the extraversion score the more likely they were to have had more than 10 sexual partners. Therefore, the predispositions an extravert may harbour perhaps allows for a greater chance of mating and the enhancement of fitness, facilitated through the impulse to seek for the novel, strive for the upmost success and mingle socially.
A greater number of sexual partners, in ancestral times, would have presumably led to more offspring – enhancing evolutionary fitness; a reason for the trait to have spread so prolifically. Yet, the availability of contraception in the 21st century, as Nettle posits, has rendered such a benefit mute. Well, not quite mute, there is still the greater number of pleasurable sexual woohoos an extravert will encounter; there’s an argument for an increase in wellbeing there, too. In summary, extraverts have more sex without the chance of having to apply the baby powder.
Extraverts, moreover, are more likely to strive for success, and hence be more successful in their chosen discipline, which would have beneficial consequences for any of an extraverts’ children, as extroverted parents would be more able to provide a materially nurturing environment through their monetary gain. Basically, extroverts have the noticeable ability of creating trust-fund babies. . .
What are, conversely, the costs of such a behavioural expression that entails sexual promiscuousness, competitive dominance and novelty seeking?
The comparably greater number of sexual partners an extrovert is likely to have enjoyed could produce a net negative effect on the effort put into actually raising their children; as Nettle put it “highly extraverted men are more likely to be involved in extra-pair liaisons, which must involve time and resources. Highly extraverted women, on the other hand, through their succession of partners, are likely to involve their children in step-parenting, which is a known risk-factor for abuse, neglect and harm to children.” So, although the children of extraverts are likely to have a few more siblings to build a treehouse, or to play fortnight with, they’re also likely to have a dreaded step-parent and, perhaps, a father that misses the occasional weekend visit.
With a need for novelty in their lived experience, extraverts seek out, and are less deterred by risk. This could have potential risks for an extraverts’ overall health, and therefore, their evolutionary fitness i.e. a severely injured or dead person cannot propagate their genes into the next generation. Indeed, Nettle found that, of his participant pool, those who had been hospitalised because of an adventurous accident had greater extraversion scores. Extraverts, in addition, tend to habituate to their experience and get bored. This could create the situation where an extravert has accumulated massive wealth and cultivated a successful career, only to risk and gable it all away for the next novel thing, leaving this said person with nothing.
Extraverts, then, enjoy novelty and abhor boredom, in both their choice of sexual partner and career. This trait, potentially, has huge benefits especially in the advent of the gig and zero-hour contract economy, whereby one can be flexible and out-going with their choice of work. If a researcher were to measure trait extroversion within the gig economy population, I’d put money on them scoring high. This all comes with a caveat, however, as extraverts are also prone to silly accidents, exposing their children to step-parenting and gambling their wealth away on their new adventure.
With great extraversion, comes great and unavoidable risk.