IQ

IQ is approximately normally distributed. 115 is typically defined as one standard deviation above the mean of 100.

IQ or intelligence quotient is the test score of a test meant to measure general or specific cognitive abilities. IQ tests contain basic cognitive tasks that do not require specialized skills, and it is generally assumed that the score will not be affected by prior training. The test items (within a subtest) are chosen to positively correlate with all the other items, i.e., that they measure the same cognitive abilities. IQ scores based on comprehensive IQ tests are highly stable when one is re-tested even over large time periods (r > .86), and IQ scores correlate moderately to strongly with school grades and work performance (especially in more cognitively demanding sectors). A test taker's raw score, the sum of correctly solved items, is compared to a large, representative sample. This is typically achieved by transforming the test scores such that the population mean is 100, and the standard deviation (a measure of how much the test scores vary in the population) is 15. An IQ of 100 means that roughly 50% of the population scored better (50th percentile, so perfectly average), and a score of 115 means that roughly 16% of the population scored better (84th percentile).

Though IQ is commonly portrayed as "just a useless number" that only suggests how well one does on paper and pen tests that do not measure "real intelligence," IQ testing has proven to have many practical applications, from discerning individuals with learning difficulties at an early age to rapid employment screening. Even though IQ is an imperfect measure of intelligence, it allows the prediction of the odds of achieving many outcomes well above chance. The prominent intelligence researcher, Arthur Jensen (1980), claimed that the most important thresholds of IQ were 115 on the upper end as the minimum IQ threshold for qualifying for admission to a graduate school. At the lower end of the intelligence spectrum, 75 was the threshold generally required to complete elementary school. As the public intellectual and psychologist Jordan Peterson has famously noted, a minimum IQ of around 83 is the absolute lowest requirement to join any branch of the U.S. military. In practical terms however, the US military generally rejects all candidates below an IQ of 93, which would exclude roughly a third of the US population from military service on this single metric alone.

IQ tests partly measure abilities that are relevant for all cognitive tasks; for example, to quickly learn, retrieve and process a maximal amount of information and to quickly consider different hypotheses without losing track of things, one needs a certain level of general intelligence (which is reflected in an IQ test result). These abilities enable one to better find a solution to any given problem and a path to any given goal. Research has indicated that higher IQ individuals generally respond to instruction quicker and more effectively by learning at a rate of 2-5 times faster than lower IQ individuals. Interestingly, even things that are commonly believed to be unrelated to IQ such as social skills correlate positively with it to some degree, but only aspects of social skills like broad social awareness, not so much the gossipy socializing aspect itself.

g-factor

Colloquially, IQ is often used interchangeably with general intelligence, or the g-factor, even though these are distinct concepts. While IQ is a test result that may measure specific abilities (e.g. verbal or spatial abilities), g is a representation of general intelligence, i.e. a general ability that predicts success in all cognitive tasks, from weakly (i.e. simple reaction time speeds) to strongly (i.e performance on a gold-standard IQ test like the Wechsler Adult Intelligence Scales tests).

The existence of this general factor is evidenced by the positive correlation between different kinds of cognitive ability and the 'indifference of the indicator', i.e. the fact that all cognitive tasks are proven to load on this factor, and that any sufficiently broad and difficult series of cognitive tasks will correlate strongly with g.

A task in which people's performance correlates with g and hence with all other IQ tests is said to be g-loaded. Anyone who scores highly on one strongly g-loaded test will tend to score highly on other IQ tests, as g explains much to most of the variance in the scores of IQ tests, and indeed, in regard to most intellectual pursuits in general. The more diverse subtests an IQ test contains and the more g-loaded the subtests are, the more accurate the measurement of g, with diminishing returns at around 13 subtests. Diverse IQ batteries containing multiple subtests are so general and comprehensive that the raw score and g correlate strongly. For example, the FSIQ given by the Wechsler Adult Intelligence Scale (WAIS), one of the broadest and most commonly used IQ tests, correlates with around r = .95 with g. FSIQ is often used as an estimate of g, and it is indeed nearly isomorpic with g (measuring the same thing), due to the broadness of cognitive abilities covered in this comprehensive IQ assessment. With IQ scores, the reduction in correspondence of g is mostly caused by the norming of IQ tests by age, with cognitive ability generally declining with age, and thus raw scores (the sum of your correct responses to all the problems in the IQ test) would be expected to correlate even more with g than deviation IQ scores.

Various physiological measures, such as reaction time, brain volume, cortical surface area, brain glucose metabolism, and color discrimation have been found to correlate with g. Further, much of g has been linked to specific genes, and g is highly heritable (up to 86% in adults, but lower in children). This suggests that more efficient and functional brains explain a large portion of general intelligence, and that g is less decided by social class, schooling, and so forth (though these do play some role). As these non-biological factors are also associated with life success, the fact that IQ tests may also be measuring them does not diminish their predictive validity in this regard.

IQ and age

IQ scores are affected by the test taker's age with cognitive ability typically peaking at around 25, and most cognitive skills remaining stable until the 50s. It also seems plausible that higher IQ individuals generally exhibit less of a cognitive decline as they age, at least they are less likely to succumb to dementia.

Older methods, being based around calculating IQ by the ratio of one's score to one's age, have fallen out of use (with these methods being designed to measure the IQ of children and prone to producing inflated scores compared to modern methods of computing scores). The scores given by most modern tests are relative to an age-matched norming group, which means that IQ is not necessarily a pure representation of raw intellectual ability compared to others in general, as some abilities decline with age (although this effect is generally small), and among children, some may initially be more precocious in this regard but then regress later with age relative to their peers. This is why it is unwise to trust the grossly inflated IQ scores often attributed to public figures that rely on tests administered as a child, even if the result is confirmed as legitimate.

Sexual desirability

The mating mind

Evolutionary psychologists such as Geoffrey Miller, with his 'mating mind theory,' have argued that high IQ in males is strongly attractive to women. They argue that this trait primarily evolved due to sexual selection pressures, claiming that human intelligence only could have developed to such a high degree because of sexual selection for intelligence. Miller claims this is due to basic survival seemingly only requiring low levels of general intelligence, and thus natural selection wouldn't have been enough for human's unusually high intelligence to evolve.

Evidence for

This theory was largely influenced by the idea that intelligence functions as an honest signal of a low mutational load due to its highly polygenetic nature. Thus Miller was suggesting that general intelligence is robustly associated with a general "good genes" factor. While some studies indicated that some purported markers of mutational load, such as fluctuating asymmetry, did correlate significantly and strongly with general intelligence, other research contradicted this. Woodley of Menie et al. later found that the link between secular trends in craniofacial symmetry (used as a rough marker of mutational load) and secular declines in general intelligence was weaker than previously believed, with mutation accumulation only explaining 7% of the secular decline. This suggests that the brain is broadly resistant to the effects of deleterious mutations on general cognitive function outside of extreme neurological conditions.

In support of the sexual selection theory of the development of human intelligence, there is some direct evidence that intelligence may be under sexual selection, with one study showing that an IQ of 120 (90th percentile) is the most sexually attractive IQ score. No gender differences were observed in this study, despite being predicted by evolutionary psychology that women should be more sensitive to partner cues of intelligence than men. Thus, this finding contradicts Miller's theory. If women use intelligence as a cue to resource accrual ability, one should expect a pronounced sex difference here. However, it does not entirely disprove Miller's hypothesis. If general intelligence is indeed an honest signal of 'good genes', one would predict both sexes would be attracted to intelligence in romantic partners. However, Miller emphasizes female derived sexual selection pressures in line with the general evo-psych prediction that women are more demanding than men, especially when it comes to short-term mating.

Intelligence is moderately associated with socio-economic status. According to parental investment theory, women are more sensitive to partner cues indicating the ability to gain resources and status than men due to their greater investment in rearing and nurturing their offspring. It is argued that men generally place a premium on fertility cues such as youth and physical attractiveness when evaluating potential female romantic partners, while women place a premium on wealth and status, at least for long term relationships. However, this study relied solely on self-reported preferences for intelligence (with intelligence presented in an abstract fashion of a certain percentile).

Another study (which only examined women's preferences) did find a weak positive effect for male verbal IQ on women's evaluations of them as potential partners (Prokosch, 2009). This study used a video rating paradigm. The design involved the female subjects viewing the male subjects performing several tasks such as reading headlines from various online news websites and answering open-ended questions before evaluating their desirability as short-term or long-term partners. The study authors chose these tasks because they correlate positively with IQ test performance. The effects of male IQ in this study were weak (only explaining 3% of the variance in female ratings across conditions). The importance of intelligence did not vary across short to long-term conditions, contradicting the idea that male intelligence should be more attractive to women regarding LTRs. However, this could be because women are more primed for long-term mating, especially when asked directly. There was also no evidence of menstrual shifts in women's preferences for intelligence. The finding of this study likely differs from other, larger-scale studies that find null effects for IQ on female ratings of males due to methodological differences, such as not controlling for male attractiveness when it came to WAIS scores as it was believed the halo effect would not bias these. However, this disregards the idea that physical attractiveness could be positively correlated with verbal IQ (vocabulary subtest). In line with other research into this topic, the study found that subjective perceptions of intelligence were much more critical in driving mating outcomes than IQ as determined by tests.

Evidence against

Other research, using standardized intelligence tests to measure intelligence and examining the correlation between IQ and partner rated attractiveness in a speed-dating and video dating context has found that only perceived intelligence and funniness are viewed as attractive in a potential romantic partner. Driebe et al. (2021) found no positive relationship between objectively measured intelligence and male desirability. The participants correctly perceived more intelligent people as more intelligent but not as funnier or more desirable), despite measured intelligence being detectable with a decent level of accuracy in short interactions. This paper combined two studies, a video rating one where only men were rated and a speed dating one where the effect of IQ on desirability in individuals of both sexes was examined. The latter study could not control for factors like SES (people wearing expensive watches, etc.),

The first study, which used a battery of IQ tests to estimate general intelligence (as opposed to the simple vocabulary test used in the speed dating studies), found there was a potential weak negative correlation between the male subject's general intelligence and the female rated desirability of the male subjects (95% CI -.26; -.01, p = 0.03).

Further, Hofer et al. (2021) conducted a speed dating study that examined the effects of various traits commonly asserted to be desirable in a romantic partner (creativity, intelligence, physical attractiveness, etc.). In concordance with the other research, it found no significant correlation between men's objectively measured intelligence (verbal, numerical, spatial) and rated desirability by their female partners.

Also, in agreement with the findings of the studies above, Hofer et al. found that perceived intelligence was associated with greater rated desirability, even controlling for physical attractiveness (which is strongly associated with perceptions of intelligence at least at first acquaintance). This research suggests that general intelligence is probably not a particularly salient factor in determining women's evaluations of male attractiveness (at least in short-term mating contexts). This lack of a link makes it unlikely that intelligence is robustly subject to female-driven sexual selection, at least in modern industrialized society (also the sociological context where Miller claims to derive "evidence" for his sexual selection hypothesis).

These findings cast serious doubt on the validity of the "mating mind" theory. If intelligence were sexually selected for, it would likely be indirectly so. The selected pressure for IQ could be driven by the fact that general intelligence is moderately correlated with status and income (in industrialized societies at least, and likely also in pre-industrial ones, perhaps not to the same degree). It is also important to note that many marriages throughout human history were arranged or otherwise subject to social/parental influence to a greater or lesser degree. Parents, in particular, seem to desire that their children are married to highly educated, wealthy, and high-status individuals, all traits that are positively correlated with general intelligence (in modern samples). Parental mate choice may have exerted sexual selection pressure for greater intelligence (particularly in males), whereas female selection pressure did not. Harsher ecologies likely also exerted more substantial natural selection pressure on general intelligence. Inter-group competition, common throughout human history, would likely also have selected for higher levels of general intelligence. This selection pressure would be especially salient among groups in regions with strongly politically fragmented states, with harsh competition for scarce resources and harsh climatic conditions.

Sexual success, reproductive success and life success

IQ and promiscuity & mating success

Many studies show consistent relationships between higher level of intelligence and lower rates of engaging in sexual activity. More intelligent people, especially at universities, tend to have less sex. One of the strongest studies establishing a negative relationship between sexual success and IQ found that teenage boys with a verbal IQ of two standard deviations above the median or above (130 IQ) were two-thirds less likely to lose their virginity compared to those with an IQ of 100. The relationship between higher IQ and lower odds of losing their virginity was linear for both boys and girls above a perfectly average IQ of 100, however, it was stronger for girls 130 IQ or above, who were four-fifths less likely to lose their virginity than girls with a perfectly average IQ of 100. However, other studies have found that such relationships do not hold when examining twin pairs, suggesting such relationships are merely correlational and not caused by IQ. Instead, it is likely that environmental differences between high and low IQ families explain such effects, which suggests that IQ per se is not generally associated with age of virginity loss, though higher IQ people will generally lose their virginity later due to these environmental confounds.

A German study suggested academics are at least twice as often incels as others (see demographics).

One reason for this may be that women have a higher level of IQ variability than men, as well ashaving a slightly lower level of general intelligence than men. The skewed sex ratio in favor of men in these highly intellectual demanding fields may partly explain the higher incel rate of men enrolled in such subjects, via a lack of ability to assortatively mate for intelligence, and an overall lack of exposure to women in general, though the co-educational sex ratio of a particular field of study seems to be only weakly associated with men's level of sexual success, and it is therefore unlikely to explain much. Other hypotheses are listed below.

A study by Rosemary Hopcroft of GSS (General Social Survey) data in the US found that, while IQ has little effect on rates of sex of individuals of both sexes, very low IQ men were generally more sexually active than very low IQ women, and higher IQ people were less sexually active overall.

Hypotheses

Nevertheless, it seems clear there is a general link between a high-IQ and a delayed sexual onset in both sexes. It is not entirely certain why this is the case, despite the numerous advantages associated with a high IQ, however many factors are conceivable:

• Alienation/mismatch of high IQ tasks: Modern highly specialized high IQ behavior (especially computer work and engineering) may be sexually unattractive being evolutionary novel (mismatch hypothesis) unrelated to communal life, and unrelated to naturally attractive behaviors like dancing, singing, humor and demonstration of physical strength. Though as there does not seem to be any major association between broad athletic ability and IQ, it is unlikely that this would be reflective on any physical inferiority on the behalf of intelligent people in general, but perhaps more of a reflection of the social roles high-IQ people would be drawn to in modern society.
• Hard sciences: Harder fields of study may have more incels as they are more evolutionary novel. They are also more time consuming and competitive, reducing time for socializing and hence for sex. Harder courses also tend to have fewer women in them.
• Feminism: The prevalence of feminism in academia may be shaming male academics to be impotent nice guys. The fact that women in Western countries are now substantially more educated than men (especially younger women) indicates that modern academia is not strongly selecting for intelligence but other traits, such as conscientiousness and agreeableness, and that particularly masculine men may be excluded by the academe. So the predominant ideology is likely also reflective of the demographics and traits of the people that are groomed for academia by the modern education system and society as a whole. Intelligent people may also be more likely to be able to correctly discern what ideology is currently dominant in society, and as Western countries are very liberal and very feminist (in historical terms), it is likely that more intelligent people in general therefore tend to conform themselves more to feminist attitudes.
• 'Beta behavior' : Intelligence has been found to be weakly correlated with pro-social behavior, with this relationship being stronger for verbal intelligence and likely explicable by common genes partially mediating both intelligence and pro-social behavior. Insofar in that it is commonly claimed that Western women in particular do not like 'nice guys', particularly when they are young and not interested in settling down with a beta provider, one would expect intelligent men to be more likely to be lumped in the 'nice guy' category and rejected by women based on this association between intelligence and pro-social behavior.
• Hypergamy: The fact that educated women are generally reluctant to date men unless they earn more money than them (see hypergamy) may increase incel rates among academics. A singledom crisis has been observed among highly educated women.
  Though it could also be argued that this would actually increase the demand on highly intelligent men as a group, due to women generally demanding at least parity in terms of social status and education when considering long-term partners and there being a moderate association between intelligence and education level. There is also a moderate positive correlation between intelligence and income.
• Environmentalism: Environmentalism may make academic men less attractive to women as they seem more likely to be drawn to that ideology, with education level being associated with lower participation in activities revolving around conspicuous consumption and greater overall awareness of environmental issues.
  This poses an issue for the sexual success of environmentally conscious men as women generally prefer men who display wealth and eat meat.
  It may also serve to generate overall pessimism and disinterest in procreation.
• Slow LH: Though cognitive specialization, crucial for success in modern society, seems linked to a slower life history speed, LHS itself seems to be generally unrelated to general intelligence, with the evidence generally showing it may only be related to how intelligence is 'invested' in certain specialized cognitive skills.
  There is however, evidence that higher levels of intelligence are actually linked to a slower life history speed on the most basic level, that is, delayed reproduction.
  Some research has indicated that the negative relationship between IQ and fertility in men reverses in some samples when age range of men included is extended to men in their middle ages, as low IQ men are much more likely to reproduce young and highly intelligent men are more likely to have children very late compared to lower IQ men.
  This study also found that more intelligent men generally had their children with a single woman, while less intelligent men were more likely to be serially monogamous. This indicates strong pair-bonding and lower promiscuity among the intelligent in general, also traits hypothesized to be associated with a slow life history strategy.
  It is also interesting to note that East Asians appear to generally have a slower life history speed compared to other major races. This Asian-slower life history link, combined with the Asian over-representation in higher education in the US, may both explain the higher incel rates among Asian men, in particular, and also may partly explain why incel rates are higher among academics (especially those in the hard sciences), at least in the United States where Asians are over-represented among the college-educated.
• Polarization with lower class: Status signaling among upper class might distinguish/polarize itself from activities in lower classes where people produce many offspring for economic reasons, hoping one child will make it (favoring fast LH), thus making rapid production of offspring viewed as uncouth behavior in higher class circles.
• Mental illness: High intelligence predicts neuroticism and various mental disorders in Mensa members and mental issues strongly reduce reproductive success. However, Mensans may not be representative as the organization requires a yearly fee in exchange for membership which may attract people who overcompensate for various flaws by boasting about having scored a high IQ. One can also submit the results of various IQ tests to join, and as IQ tests do not correlate perfectly with each other, an outlier result can be used for admission, so this also selects for people who are particularly keen to join in order to brag about their high IQ. Famously, Stephen Hawking said, “joiners are losers”. Studies on the general pop show a weak positive link between IQ and mental stability.
• Inhibition, cautiousness and responsibility: Higher levels of intelligence may be generally associated with greater cautiousness and a propensity to 'overthink' situations which results in lower levels of impulsive and irresponsible behavior. There is evidence that prison inmates with higher IQ's are more well behaved. High IQ people have fewer conduct problems in school and higher job performance as well Some low IQ couples are so impulsive they even have sex in school, in the back of the classroom, during the lesson.Impulsivity appears to be a strong predictor of sexual success, particularly among men, with teenager boys with ADHD having twice the number of sexual partners, it being found a variant in the dopamine transporter gene associated with impulsive behavior is associated with a 80-100% higher lifetime sexual partner count among adult men, and there is also evidence young people who drink more alcohol have much higher likelihoods of having recently had multiple sexual partners. Thus, if intelligent people are less likely to behave impulsively and engage in risky behaviors like binge drinking, this could partly explain the lower partner counts among the more intelligent, as cautious, responsible behavior appears to curtail many opportunities for engaging in casual sex. Behavioral inhibition could also be directly unattractive to women, as some studies only find a relationship between genes for impulsiveness and sexual partner count in men, though this relationship could be due to women's more passive courtship style, with men generally expected to perform the initial approach and escalate first every step of the way up to sex.
• Assortative mating: there is substantial assortative mating for intelligence (people preferring to form relationships with those of roughly similar intelligence to themselves). As there are exponentially more men than women at very high levels of intelligence (> 130), it could be that these men may struggle more to form romantic relationships with women than less intelligent men, due to the much fewer amount of women with a similar level of intelligence to themselves. This is assuming that women don't exhibit hypergamy in terms of intelligence, which would be predicted somewhat by their preference for men with higher levels of status and resources, the attainment of which is moderately associated with intelligence.
• Low IQ is actually attractive to women: Low IQ men have more sex. A study conducted by Halpern et. al (2000) found the most sexually active individuals were in the 75-90 IQ range for males, with these males being found to be the least likely to be virgins as adolescents. An IQ below 70 is generally considered to constitute an intellectual disability. 46.7% of low IQ men were sexually active, while only 18.4% of low IQ women were. Thus, low IQ men were 2.5x as likely as low IQ women to be sexually successful.
  There is also evidence that IQ and scores on highly g-loaded standardized tests may be weakly negatively associated with female evaluations of male romantic desirability.
• Endogenous personality: The psychiatrist and former evolutionary psychologist, Dr. Bruce Charlton, has claimed that genius is characterized by an "endogenous personality" centered around inward motivation and social disinterest. He uses this theory to explain why many noteworthy historical geniuses were often socially isolated, sexually unsuccessful, childless and did not achieve evolutionary success in terms of maximizing individual fitness.
• Bioenergetic tradeoffs: Though some evidence (noted above) indicates that more intelligent people are partly more intelligent because their brain is more efficient at utilizing the energetic resources available to it on a cellular level, it is important to note that the human brain in general is extremely energetically demanding, even relative to its large size. It could be that there is a trade-off involved at a basic level between investment into large brains and investment into other physiological functions, which could include general mating effort, level of social involvement, competitiveness etc. There is a limited amount of evidence that there is a potential energetic tradeoff at play between larger brains (associated with greater intelligence) and fertility, with one Swedish scientist discovering that guppies he had deliberate bred for greater intelligence and larger brains had reduced fertility as a result. Thus suggesting a basic energetic tradeoff between intelligence and reproductive success in most animal species, with greater encephalization (size of brain relative to body) also seemingly being associated with lower fertility, cross-species.

IQ and fertility

Cross-culturally, status increases male reproductive success, and intelligence and linked factors such as occupational prestige and knowledge boost male status. The effect of IQ on occupational prestige is strong, though predominantly mediated via education, and thus it would be expected that IQ would be beneficial in promoting men's reproductive and overall mating success, though not necessarily women's reproductive success, due to factors such as hypergamous mating, shorter female fertility windows, and, in more sexually egalitarian and developed countries, the trend for men to be increasingly less educated than women, which ties in with female hypergamous/homogamous selection for education in male partners.

However, studies have found negative relationships between IQ and fertility in modern samples, though this negative relationship is generally more pronounced among women than men, which is broadly in line with evolutionary psychological predictions. This effect seems to be mainly driven by education rather than IQ per se, with more intelligent and thus generally more educated women delaying marriage & reproduction to focus on schooling, reducing highly educated women's lifetime reproductive success, which seems to be partly driven by women's shorter fertility windows and the greater tendency of highly educated women to be childless.

Another study found that among women, a one-standard-deviation increase in childhood general intelligence (15 IQ points) decreases their odds of parenthood by 21–25%.

Among men, evidence indicates there are differential effects on reproduction and mating behavior than what is generally found among women. More importantly, as IQ is moderately associated with lifetime income in both sexes (with a large part of this effect being driven indirectly via education level) it is important to disaggregate the impact of education level, income, and IQ when seeing if IQ per se is negatively associated with reproductive success in men. A 2006 analysis of US GSS data conducted by Rosemary Hopcroft found that greater income increased sexual frequency for men, while high IQ alone was associated with lower self-reported sexual frequency. The same trend was found for men's reproductive success, with higher IQ driving lower fertility among men, while higher income was associated with higher fertility among men. Additionally, this study indicated that income and IQ exerted distinct effects of sexual dimorphism in reproduction rates among men and women in the sample. That is, higher-income men had greater fertility than high-income women. In contrast, high-IQ men and women had similarly low fertility levels when the author controlled income and education. Hopcroft commented this might support the idea that high IQ, at least on the group level, may be maladaptive in the long run as it generates cultural selection pressures that counteract evolved fertility preferences among individuals of both sexes. An example that supports this contention would be the demographic transition phenomenon where more educated and wealthy countries generally have lower fertility the more these characteristics diffuse among the population.

The relationships between IQ and fertility vary cross-culturally, even among WEIRD (Western, Educated, Industrialized, Rich and Democratic) countries. In Sweden, income is associated with fertility among men and women, like in the US, with high-income women having lower fertility. Much of this effect, however, is driven by very low-income women being less fertile in Sweden than in the US. The relationship between income and fertility among men in Sweden is monotonic, with no diminishing returns for men's income and reproductive success at greater levels of wealth. Contrary to Hopcroft's GSS study, Kolk & Barclay (2021) found high IQ is associated with slightly greater fertility in Swedish men, independent of income and education. Much of this positive association is explained by higher-IQ Swedish men being more likely to be married than lower-IQ men. However, the effect was preserved when accounting for marriage. This study was a replication of an earlier paper by the same two authors, which found the effect of IQ on attained fertility was most pronounced among the lowest IQ cohort of males, who had the lowest fertility.

A Finnish study found that higher education positively predicted fertility for men, but the opposite was found for women, though IQ wasn't directly examined. This study found this positive relationship for men was primarily driven by shared environmental and genetic factors and was again primarily driven by highly educated men being more likely than low-educated men to attain a stable female partner in adulthood, as was discovered in Sweden.

Cultural and national-level economic factors, such as the greater leveling of wealth in more socialist Scandinavian countries and higher religiosity among Americans (which promotes fertility but is also associated with lower IQ on average), the relatively more generous Scandinavian welfare state, and levels of overall cultural conservatism, among other things, may explain these cross-national differences if they prove to be robust.

However, the link between lower IQ and lower fertility may not be completely mediated by factors such as attained status and wealth, where this relationship is found. There is evidence that IQ is positively linked with several general health parameters such as longevity, and also to general health (when controlling for socioeconomic status differentials). IQ even seems to be linked to other general health markers such as handgrip strength, seemingly even when lifestyle confounds such as exercise are controlled for. Furthermore, there is some evidence that infertile men have lower average IQs than fertile men. As fertility is a reliable biomarker for overall male health, and in light of the fact that more physically healthy men tend to have more children, the link between IQ and general health would be expected to influence the observed relationships between IQ and fertility.

Executive functions

More speculatively, a synthesis of the above data would suggest that the men with the highest risk of being lifelong childless would tend to be low-educated, low-status, low-income, and (generally) low-IQ men. However, there may be strong mating and/or reproductive skew among this class of men. In contexts where male IQ predicts lower fertility, the high-IQ cohort of men with lower overall fertility would tend to be maladjusted high-IQ men who have attained a lower educational and occupational status than their IQs would predict. Such maladjustments, despite high IQ, as well as being influenced by personality, motivation and social factors, are generally associated with relative deficits in executive functions (higher-order mental processes such as mental flexibility, self-control and working memory), which, while having overlap with intelligence, are also partially distinct. Executive functions are also one of the most heritable traits, even moreso than IQ, being 0.99 heritable, which means environmental factors have nearly no influence on their development. Executive functions also independently predict status criteria such as educational attainment.

However, deficits in executive functions are linked to neurological disorders such as ADHD, autism, and bipolar disorder. These conditions are also independently associated with lower fertility, particularly in men though this does not seem to hold for ADHD, at least among women, and on the genetic as opposed to the broad phenotypic level. Therefore, executive functions could only be predicting lower fertility and attained status indirectly as a symptom of broader cognitive disorders.

Additionally, deficits in executive functions may be linked to one's life history strategy, particularly the less cognitively complex aspects such as impulse control and behavioral self-regulation. The slower life history strategy centred around deferred reproduction has been linked to greater overall fertility in both sexes in the United States and Sweden. In Germany, prospective slow life strategies traits such as morning orientation and a lesser tendency towards stimulus-seeking behavior, together with more clear slow life strategy traits such as overall lifetime sexual restraint and a greater monogamous mating orientation, were also associated with greater lifetime reproductive success in both sexes.

Thus, it is possible that if executive functions are linked to a fast life strategy, this may be maladaptive in many instances in modern societies with greater access to fertility-suppressing reproductive technologies, as much fertility is taking place in the context of long-term, monogamous relationships. As a result, men with extremely low executive functions may generally have issues maintaining long-term romantic relationships, and a lower inclination towards them, thereby suppressing their fertility.

This explanation is not mutually exclusive with an alternate explanation that poorly educated and low-status men, which men with executive functioning deficits would be more likely to be, are generally less desirable to women and less likely to be mated, mirroring greater female preferences for status in long-term versus short-term relationships, and also supported by evidence that suggests lower long-term relationship stability when women are 'dating down' in status.

'Troubled genius' trope

Some people argue that outlier high-IQ is associated with general social maladjustment, possibly caused by difficulties in social intercourse among people of different intelligence levels. This greater social maladjustment on behalf of the very intelligent, if accurate, would suggest a link between extreme levels of intelligence and involuntary celibacy as social exclusion and low achievement do not tend to be generally good things regarding men's romantic prospects.

This idea was first expounded upon at length by a member of several high-IQ societies, Grady M. Towers, who wrote a famous article called "The Outsiders" for the journal of the Prometheus society (a society for people at or above the 99.997th percentile of IQ), Gift of Fire. In his article, drawing on research into intellectually gifted children produced by the psychologist's Lewis Terman and Leta Hollingworth's investigation into the effects of intelligence on leadership, Towers argues that intellectually brilliant people ofter suffer a profound sense of social alienation brought on by difficulties with schooling (with the unstimulating material provided being claimed to often lead to laziness and ennui on behalf of the superbright student), the lack of peers of similar intellect to themselves. Others argue a qualitative difference in thinking ability is reached when one exceeds a certain IQ threshold (stated to be around 150), which naturally hampers effective communication between extremely high IQ individuals and people below that threshold.

In the course of his piece, Towers mainly draws upon anecdotal evidence of the often tragic lives of several outlier high IQ people, repeatedly referring to the tale of Williams James Sidis, a child prodigy often stated to be the most intelligent person who ever lived. Sidis is notable for such fears as having invented his own language before the age of 8 and graduating from Harvard University at 16. Sidis died at the age of 46, in poverty and likely a virgin (as an aside, it is interesting to note that Sidis was also probably not voluntary celibate as has commonly been asserted as he was described as having an unrequited love for an older girl after his adolescent oath of perpetual celibacy).

Given the lack of public recognition his intellectual accomplishments achieved during his lifetime and his bleak and lonely life, Sidis is viewed by many as an archetypal example of the pitfalls of being intellectually precocious, with it often being proclaimed that Sidis was a complete failure in life despite his childhood brilliance. However, Sidis did leave behind a substantial literary corpus containing his polymathic and deep knowledge of the sciences, mathematics, philosophy, and American history, often written under pseudonyms. Some of his ideas influenced later geniuses. Official research has found no evidence of a negative relationship between IQ and positive life outcomes in general. In a large general population sample, several positive life outcomes, such as health, educational attainment, social functioning, and wealth, are linearly associated with IQ. However, as it is nearly impossible to gather large, representative samples of outlier high IQ people, this doesn't necessarily reveal much about the lives of intellectual outliers such as the extremely intelligent.

For the evidence that extreme intelligence is sometimes associated with adverse life outcomes, we can turn to psychologist Lewis Terman's long-running genius study, one of the very few studies that examined a large group of outlier high IQ individuals over a long period. Terman sought to debunk the idea that intellectually precocious children were often maladjusted. Indeed, while Terman found that his subjects, commonly dubbed "Termites," were physically healthier than typical children of the same age and considered particularly well adjusted socially and psychologically, when his "Termites" were tested again later in adulthood, there was evidence of a linear relationship between scores on a test of verbal intelligence and maladjustment.

Notably, fully half (45%) of the men tested that were at the highest range of ability (a verbal IQ of over three standard deviations above a sample of university graduates, Flynn effect corrected, so over 160) exhibited social or psychological maladjustment.) Similarly, it has been asserted based on studies that have examined the intellectual capabilities of high achievers in scholastic fields that the extremely intelligent may be underrepresented in eminent intellectual fields more than would be predicted by the distribution of IQ scores in the general population. Some argue that some of the underrepresentation of people with high IQ in certain professions is a function of most of the economic growth in modern societies concentrating in STEM fields, drawing on claims on high scores at certain colleges on standardized tests such as the GRE (which is not a valid measure of group IQ in such samples anyhow, as such schools explicitly select for high scores on such tests). This argument, of course, still leaves open the possibility of more verbally tilted outlier intellects being selected against by such professions.

Ineffective social and institutional infrastructure

As society, in general, is crafted to cater to people in the normal range of intelligence, this could inevitably result in adjustment issues for people who fall well out of the range of 'normality' when it comes to intellectual functioning.

It could also be the case that the institutions originally meant to cater to the highly intelligent, such as universities, are often incapable of recognizing the abilities of highly intellectually gifted correctly individuals, leaving them without intellectual peers who can assist them in actualizing their superior potential and a supportive and engaging intellectual and social environment in which to do so. Anecdotally, the man with the highest score on the Mega Test (a special high range IQ test), Christopher Langan, has commonly spoken of his difficulties with the conventional schooling system and claims a combination of a lack of sufficiently challenging material in high school and (seeming) intellectual envy from certain members of the faculties of institutions of higher learning stifled any progress he could have made in academia.

In their book The Genius Famine, evolutionary psychologists Edward Dutton and Bruce Charlton outline the argument that modern academia is primarily made up of cognitive all-rounders and highly agreeable and socially skilled personalities, which they argue are traits that are generally inimical to the fostering of genius in said institutions. Instead, they put forth the claim that such institutions actively select for bureaucratically minded middling intellects, often female, which they dub the 'head girl' phenomenon. They propose a genius-genius mentorship system as the solution to the decline of academia, arguing that this is the only way to reverse failing rates of innovation and regression to an intellectual dark age brought on by apparent dysgenic trends in average intelligence.

Low SES background

Some exceptionally intelligent people who fail to achieve conventional intellectual success may be disadvantaged and from low SES areas and are therefore less able to get into the elite and also high SES and high IQ environments needed to bring their abilities to bear and achieve social recognition for them. A prominent example here would again be Christopher Langan, who, while his mother was the daughter of wealthy shipping executive, was raised in an impoverished low SES environment with a stepfather who abused him. This situation contributed to his decision to drop out of college despite his perfect SAT score and good academic results. Indeed, the Terman high IQ children study found that underachievers (subjects who achieved low occupational status later in life) disproportionately came from "poor neighbourhoods, in badly cared for or slovenly homes, where attitudes towards the child were negligent" and "rural areas or small towns." This may also be partly attributable to other traits important for life success, such as conscientiousness, being both partially heritable and lower in low SES individuals on average, however.

Communication and leadership gap theory

One possible reason for the phenomenon of the underachieving genius is that while essential communication is still obviously possible among people that are very different in IQ, effective or highly persuasive communication may be more difficult, which is called the "IQ communication gap theory". Proponents of this theory generally claim that effective social communication between two individuals requires a rough similarity in IQ (usually claimed to be within two standard deviations between each other so within 30 IQ points) and that exceeding this gap makes it difficult for very intelligent people to convincingly express themselves in a way that results in persuasive, effective communication. While the 2SD figure cited by Towers and Hollingworth is arbitrary and dubious, there is some evidence that two individuals have to be within a certain level of intelligence to each other for deep communication between them to occur. In the 1980s, psychologist Dean Keith Simonton showed evidence that the optimal distance between individuals for influence and leadership was 20 points, with further IQ beyond that leading to diminishing returns in terms of social influence. The relationship between superior intelligence and influence possibly reversed after that level. The most substantial evidence cited in favor of Simonton's hypothesis was the fact that certain social groups had a specific range of intelligence included within them and that after this range was exceeded, individuals were typically excluded from the group or disengaged from it voluntarily. Simonton's research suggests that there was not only a "communication gap" in terms of ability to fully grasp the intentions and ideas of the super-intelligent on behalf of their intellectual inferiors but also a gap in which people could not effectively discern whether the person in question was more intelligent or competent than themselves. This seeming empathy gap between the more and less intelligent does suggest that outlier high IQ people are sometimes perceived as odd by others due to differences in interests, values, and the quality and nature of their thoughts, as suggested by Towers and Hollingworth.

Social factors

It could also be that reverse-hierarchies play a role in this, i.e., people are often hostile and envious towards people whose intelligence they perceive outstrips their usefulness to the group in terms of competence, especially as they may not be able to correctly gauge the competence level of people much more intelligent than themselves. Intelligent people who do not conform to the group's norms or interests may also prevent a greater threat and they may be distrusted for their perceived greater ambition for power and ability to attain it. The social value of intelligence and its association with a plethora of positive life outcomes could also naturally attract envy towards the highly intelligent, especially if they lack social graces and therefore come across as arrogant.

Assortative mismatches

Another factor could be that outlier high IQ people are often socially isolated out of preference. As people tend to befriend, marry, and like those who are similar to themselves in traits like personality, social status and even looks, it would not be surprising if the same effect would be discovered to hold for intelligence.

Indeed, a network analysis conducted by Flakus et al. (2021) found evidence that supports this hypothesis. They found that while intelligent high-school students were more often nominated as the most likable people by their peers, this liking was not often reciprocated, with intelligent students less likely to nominate others. However, this effect weakened over the period of a year until it became non-significant. This study also found an interaction effect between similarity in intelligence and the likelihood of liking a peer, supporting the idea that people of similar levels of intelligence tend to like each other more, limiting the social opportunities available to intellectually brilliant people. However, this study implies any such effect would be driven by the more intelligent person avoiding interactions with less intelligent peers. Intelligence in this study was measured by the Raven's Standard Progressive Matrices (SPM), which severely lacks discriminative ability in the very high ranges of intellect. Therefore, this study likely underestimates the effects of disassortment in intelligence on social outcomes.

IQ as a necessary but not sufficient condition for success

Finally, IQ, though it is moderately correlated with favorable life outcomes on a group level, is not the only factor that contributes to success, including in highly intellectual fields. Conscientiousness, motivation, luck, creativity, specialized knowledge, physical propinquity, social connections, and other traits often play a role in determining high levels of intellectual achievement. Some have argued that the interactions between these traits to not only be additive but multiplicative, meaning that the combined effect of these traits is greater than the sum of their individual effects. Ergo, one would expect IQ alone to be a relatively weak predictor of outstanding life and intellectual achievements, and the more specific and rare the achievement the weaker the role IQ alone would play in predicting these outcomes accurately. Thus, underachievement relative to the rarity of IQ can be expected in not only a small minority but also in a significant portion of very high IQ individuals. In this regard, high IQ individuals that are underachievers can be perceived more as victims of the excessively high expectations society places on high IQ individuals rather than as being the victims of the envious less intellectually talented. This can be viewed as an example of the statistical phenomenon of the 'tails coming apart' at extremes, i.e. that fact that predictors of another trait exhibit diminishing returns at extremes of the predictor trait and vice versa.

Furthermore, IQ tests correlate imperfectly with latent general intelligence (leaving aside the arguments over the distinction between 'intelligence' and g). A person who scores exceptionally high on one test is expected to regress substantially on another test on average, which also contributes to the error involved in the predictive validity of IQ on the individual level. Childhood ratio IQ scores are also different from adult deviation IQ scores (measuring mental development relative to age rather than mental ability relative to others) and often regress substantially with full cognitive development. In conclusion, many IQ tests administered are not broad tests but ones that only measure narrow abilities, and as well as being less accurate measures of g, certain types of these lower-order sub-abilities may predict achievement in certain fields moreso than others. This is displayed in the phenomenon of 'ability tilt', where for example a person may have a high verbal IQ but a relatively mediocre non-verbal IQ and would thus be expected to do better in realms that rely more on verbal ability.

IQ and physical attractiveness

There is a strong relationship between perceived intelligence and physical attractiveness, in line with the general 'what is beautiful is good' stereotype (that is, the halo effect that exists for beauty). Despite the large connection between individual's judgements of people's intelligence and their looks (at least at first acquaintance), it is uncertain whether these judgements have a grain of truth to them or not.

Certain evolutionary theories do predict that intelligence and physical attractiveness in humans would be expected to be correlated with each other due to the purported existence of a central 'good genes' factor that unilaterally increases fitness, however, robust empirical evidence for this claim is lacking.

Research

While some studies show dramatic links between intelligence and physical attractiveness, these studies often suffer from serious methodological flaws such as using less accurate tests of general intelligence, using low numbers of raters, or have the ratings themselves confounded by potential halo effects. For example, it is quite possible that as such studies employ interview methods, smarter people are rated as more physically attractive due to their demeanor and generally higher social status, as perceptions of higher social status seem to prompt people to evaluate others as being more physically attractive. Such studies also use low numbers of raters, making the ratings unreliable. Furthermore, IQ and general intelligence are not entirely the same thing (with IQ being a good, but imperfect measure of g), and it is more important to demonstrate a link between latent general intelligence and looks than between looks and IQ per se. Thus, high quality studies using comprehensive assessments of intelligence and psychometric models are likely needed to clarify any proposed links between general intelligence and physical attractiveness.

In contrast to studies that claim a strong link between IQ and looks, higher-quality studies like Mitchem et al.'s analysis (2015) of 1,753 identical and fraternal twins and their siblings, find no correlations between facial attractiveness and IQ. This study, was however underpowered to detect a potential tiny positive correlation between IQ and looks (r = 0.03) proposed by previous research.

Judge et al. (2009), did find a small (r = 0.16) correlation between looks and general intelligence, however this may have been caused by his sample being middle aged. Intelligence is linked with greater health, and part of this may be attributable to lifestyle factors. Thus, the link between IQ and health may only become manifest with greater age due to the tendency of higher-IQ people to age more gracefully. On the other hand, such research may indicate that the weak good genes factor is indeed causing this link between intelligence and health, and that this furthermore promotes a tendency for greater physical attractiveness in more intelligent people, as physical attractiveness is also generally linked to better health.

It may also be the case that IQ is mainly linked to looks in the case of 'bad genes', or neurodevelopmental, chromosomal, or other genetic conditions that both negatively influence physical attractiveness and IQ. Earlier studies did find a significant effect for looks only among unattractive individuals, though Mitchem et al. did not find any evidence for such non-linear effects. The association was non-significant throughout the entire range of physical attractiveness and IQ examined. The study also examined if the environmental correlation between IQ and looks was negative, i.e if high IQ people are better looking on the genetic but not on the observed level due to the effects of different environmental factors. They discovered no evidence to support this claim.

However, other research has indicated that general intelligence is weakly correlated with facial symmetry, providing some support for the integration of IQ into the proposed general good genes factor. Other studies have linked greater physical attractiveness to lower reaction time variability, a correlate of general intelligence that may indicate that better looking people tend to have sounder nervous system functionality.

IQ and mate preferences

Though intelligence and looks are not strongly related to each other, or related to each other at all in general, intelligence may play an important role in the perceptions of and preferences for looks in opposite sex partners. Aesthetic judgement is quite strongly correlated with general intelligence (.60), although this specifically concerns preferences for design and 'good' artistic taste. This strong relationship between intelligence and superior aesthetic discrimination may be applicable to preferences for beauty in other people. One interesting study that may provide some indirect evidentiary support for this hypothesis indicated that the halo effects for beauty concerning certain traits such as intelligence are stronger among more intelligent individuals. While the increase in biased perceptions found in this study among more intelligent people could be due to them preferentially desiring others they perceive as more intelligent as romantic partners (in line with the general principle of assortative mating) and thus rating these people as more attractive, it is also plausible that the superior aesthetic discrimination found among the intelligent plays some role here, serving to strengthen the halo effect found for beauty.

Stereotypes and potential explanations

Stereotypes often portray male models as being less intelligent, as evidenced by movies like Zoolander 1 and 2 and the Netflix series Zoolander: Super Model, which satirically depict male models as not being smart. This perception may stem from the fact that most male models come from lower-middle-class backgrounds and often lack college degrees. In contrast, many actors hail from upper-middle and upper-class backgrounds and possess college degrees, potentially leading them to look down on male models. Although it is unclear whether attractive women possess average intellect, there is greater variation in their educational and professional achievements compared to male models. There are more college-educated female runway models, as well as attractive women in prestigious positions, such as politicians and surgeons. On the other hand, several historical geniuses and outstanding individuals in high IQ fields, such as Einstein and Blaise Pascal, as well as some past Field's Prize medalists, are considered physically unattractive. Occupational selection effects may contribute to these differences in attractiveness across various fields. For example, modeling primarily requires good looks and posing skills, resulting in a lower intellectual threshold for success. In contrast, fields like mathematics place less emphasis on physical appearance and social skills, selecting instead for high quantitative and spatial abilities. Since spatial ability is generally considered a masculine trait, and the high systematizing ability required for mathematics correlates with autistic traits, this may explain the higher physical masculinization often observed among individuals in these fields. The combination of high masculine traits and low overall physical attractiveness can lead to particularly low attractiveness judgments, compounded by a lack of grooming often associated with autism and autistic traits, resulting in the stereotypical unkempt and unattractive appearance of people in these fields. Success in the entertainment and related industries seems to be influenced by both IQ and physical attractiveness. These convergent selection processing for both traits might explain reports of physically attractive Hollywood actors and entertainers having high IQs, even though some of these claims may be exaggerated or false.

These negative, 'horn effects' for looks and perceived IQ may also stem from envy. It is commonly believed that people that are exceptionally blessed with one socially desirable trait must have some deficiencies to 'compensate' for this, like the false stereotype that athletes are dumber on average or that strength is negatively correlated with IQ when there exists evidence that smarter people also tend to be physically stronger on average (though some of this effect could be because certain cognitive disabilities are associated with poorer grip strength). In short, people like to cope that desirable traits like intelligence and physical strength generally come with strong trade-offs that may not exist in reality, and often cherrypick examples of individuals high in one desirable trait but low in another to make this point.

It is also important to note that people who are both exceptionally good-looking and have exceptionally high IQs are rare. As a rough example, assuming a perfect normal distribution for both traits (they aren't in reality, but close enough for example's sake) and that looks and IQ is completely uncorrelated, the likelihood that a person would be exactly two standard deviations above the median for both looks and IQ is around 1:1924. This figure may be off a bit when taking into account potential sex differences in physical attractiveness and greater male variability for IQ, as well as the likely non-normal distribution of these traits at extremes. IQ and looks are obviously also both continuous variables so this example mainly serves to demonstrate how increasingly exponentially rare it is to be high in both traits as they increase. Thus, people that are both very bright and very good-looking are relatively rare, and their rarity goes a long way in explaining why groups of high-IQ individuals rarely have exceptionally good-looking people among them and vice versa, especially when no selection is exerted for both traits simultaneously in a particular field.

Summary

In summary, while there is a perceived link between intelligence and physical attractiveness, empirical evidence to substantiate a biological link between the two is inconclusive, tending to favor the conclusion that such a link is non-existent or very weak. Measurement error may play a role in this, and higher quality research is needed. Intelligence does appear to play a role in how individuals perceive attractiveness, possibly due to higher aesthetic discrimination capabilities among more intelligent individuals. However, the nature and extent of this relationship remain subjects for further investigation. Stereotypes, often perpetuated by popular media, contribute to the perception of a dichotomy between looks and intelligence. Furthermore, the notion that exceptional gifts in one socially desirable trait must be offset by deficiencies in another, is not empirically supported. This perception may be fueled more by envy and societal expectations and selection effects than by any biological or psychological trade-offs. Furthermore, individuals who are both exceptionally attractive and intelligent are likely statistically rare, despite people expecting highly attractive people to be more intelligent due to the Halo Effect. This may promote the idea that exceptionally good-looking people are actually stupid, due to the clash in perceptions of their initial perceived intelligence and their true level of cognitive ability.

IQ and height

Studies have found a weak, but significant and robust correlation between IQ and height (around r = 0.2-0.3 depending on age when tested and type of ability measured). Different explanations for this correlation exist, ranging from superior childhood nutrition increasing both height and IQ, assortative mating for both height and IQ leading to them being genetically linked, or even that taller people have greater cortical volume in the brain, leading to greater intelligence on average. The association may be explicable by a general fitness factor linking intelligence and height, along with other traits, due to assortative mating regarding fitness promoting traits.

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See also

• Personality
• Nerd
• Mensa
• Eugenics
• Good genes hypothesis
• Idiocracy
• Beauty