IQ or intelligence quotient is a measure of a person's cognitive ability. IQ is generally measured with tests that contain cognitive tasks that are very general and do not require specialization or schooling beyond a minimal level (common sense tasks). It is assumed no specific training has taken place for the IQ test. Still, modern IQ tests are also fairly sturdy and reliable (they resist the training effect, the individual items are measuring the same thing, and scores are fairly stable when one is re-tested, even over very long periods of time).
One's overall performance in these tasks (the sum of subscores) is then compared to a large, representative sample. An IQ score is computed such that the population mean is 100 points, and one's score is then calculated by converting the overall 'raw scores' (based on how well you do on the tasks) to a standardized score, measuring how you compare to the rest of the population. One standard deviation represents 15 IQ points in most modern tests, though different tests use different SDs, making numerical scores derived from distinct tests not necessarily equivalent. This IQ score is affected by the test taker's age; 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.
Colloquially, IQ is often conflated with general intelligence, or the g-factor, in short g. Unlike IQ, g is not a test result. Instead, it is construct derived via statistical analysis that is argued to represent or be associated with an underlying biological factor related to latent intelligence. A task in which people's performance correlates with g and hence with all other IQ tests is said to be g-loaded. The existence of this general factor is evidenced by the robust positive correlation between different aspects of intellectual ability (math, reading, logic). Anyone who scores highly on one strongly g-loaded test will tend to score highly on others, as this factor is generally the largest source of the individual variance in scores in these tests, and indeed, in regard to most broad intellectual pursuits in general.
As an example of the relation between IQ and g, the FSIQ score (full-scale IQ) given by one of the broadest and most commonly used IQ tests, the Wechsler Adult Intelligence Scale, correlates very highly with g (around .94 for the WAIS-IV FSIQ). The more diverse sub-tests 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.
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 at a physiological level, along with other innate and inheritable traits. It is not merely determined by social class, schooling, and so forth (though these do play some role). As these things are also associated with life success, the fact that IQ tests may also be measuring them does not necessarily diminish their predictive validity in this regard.
Usefulness of IQ
Performance on different IQ tests, school grades, work performance and attained SES all correlate somewhat (r = 0.5 to 0.6) which means IQ tests can predict general intelligence, short g, an overarching factor that is said to predict ability to act intelligently in any cognitive task, even those tasks which haven't been tested.
General intelligence becomes more predictive of task performance the more complex the task is. This means IQ tests can be used for screening. Even though IQ is an imperfect measure, it allows to very reliably decide the chances of achieving certain outcomes. Jensen (1980) claimed that that 115 was the minimum IQ threshold for qualifying for admission to a graduate school, and at the lower end of the intelligence spectrum, 75 was the threshold generally required to complete elementary school, and a minimum of around 83 is the absolute lowest requirement to be able to join any branch of the U.S. military, with the typical score required on the ASVAB (Armed Services Vocational Aptitude Battery) test to join being higher, equivalent to an IQ of around 92. Even social skills are g-loaded, but only things like knowledge about social events, not so much the gossipy socializing aspect.
Abilities that are relevant for all cognitive tasks and that determine g are for example to quickly learn, retrieve and process a maximal amount of information and to quickly consider different hypotheses without losing track of things. 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.
IQ and desirability
Evolutionary psychologists such as Geoffrey Miller, with his 'mating mind theory,' have argued that high IQ is attractive. They argue this trait mostly 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. This is due to basic survival seemingly only requiring low levels of general intelligence. There is indeed some 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.
An important fact that no gender differences were observed in this study, despite it often being predicted by evolutionary psychologists that women should be more sensitive to partner cues of intelligence than men. This prediction is due to intelligence being 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 rearing and nurturing their offspring than men. 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. The lack of sex difference in preference for intelligence, therefore, may indicate that if intelligence is/was under sexual selection, this selection may be in the form of selection of intelligence as a 'ornament', rather than it being desirable due to it being an indicator of good genes.
However, this study relied solely on self-reported preferences for intelligence (with intelligence presented in an abstract fashion of a certain percentile). Other studies, 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, have found that only perceived intelligence and funniness are viewed as attractive in a potential romantic partner. There was no positive relationship between objectively measured intelligence and desirability (with more intelligent people being correctly perceived by the participants as more intelligent but not as funnier or more desirable), despite measured intelligence being detectable with a decent level of accuracy in short interactions.
The first video rating study mentioned above, which used a battery of IQ tests to estimate general intelligence (as opposed to the simple vocabulary test used in the speed dating studies) actually found there was a possible 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). It is important to note that the first study also controlled for factors positively associated with both intelligence and male mate value due to the moderate correlation between IQ and socio-economic status (such as displays of wealth, like expensive clothing and wristwatches, etc.). In contrast, it was impossible to control for such factors in the second series of studies due to the speed-dating paradigm used.
IQ and sexual 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. A study on the relationships between verbal intelligence and virginity rates 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 boy 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.
A German study suggested academics are at least twice as often incels as others (see demographics). Among women, a one-standard-deviation increase in childhood general intelligence (15 IQ points) decreases their odds of parenthood by 21–25%. Among university age individuals, a study from MIT suggested incel rates vary considerably between different fields of study, being the highest for biology and the hard sciences, and lowest in the humanities.  It is important to note that the hard sciences generally have individuals of a higher IQ than those in the humanities on average (apart from philosophy), and the higher the average IQ of a major, the less women will be enrolled in that subject. This lines up with the fact that women's IQs have a lower level of variability than men, as well as women having 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, 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.
Nevertheless, it seems clear there is a general link between a high-IQ and a lower lifetime sexual partner count 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), unrelatable, unrelated to communal life, and unrelated to naturally attractive behaviors like dancing, singing, humor and demonstration of physical strength.
- 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: Prevalence of feminism may be shaming male academics to be impotent nice guys.
- '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: Educated foids being reluctant to date less educated men unless they earn substantially more (see hypergamy) may increase incel rates among academics. A singledom crisis has been observed among highly educated foids.
- Environmentalism: Environmentalism making academic men less attractive to women as they are not as materialistic. Also serving to generate overall pessimism. Women actually prefer men who display wealth and eat meat.
- Slow LH: Professional specialization generally favors slow life history speed (LH), though LHS itself seems to be completely unrelated to general intelligence, perhaps only being related to how intelligence is 'invested' in certain specialized cognitive skills. There do seem to be differences in life history speed between races though, with Asians supposedly exhibiting a slower life history speed in general compared to other major races. This Asian-slower life history link, combined with the Asian overrepresentation 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 overrepresented 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) which may be seen 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. Famously, Stephen Hawking said, “joiners are losers”.
- 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.Overall the science points to substantial dysgenics regarding intelligence. Some also speculate that assortative mating in IQ (spouse correlations ~0.40) will lead to lower social mobility among the less intelligent, perhaps even leading to caste systems based on IQ forming.
IQ and looks
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, however, robust empirical evidence for this claim is lacking. 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, and the ratings themselves being seriously confounded by potential halo effects. Higher-quality studies, such as a recent meta-study of 1,753 identical and fraternal twins and their siblings, generally find no correlations between facial attractiveness and IQ.
Though intelligence and looks are not strongly related to each other, intelligence may play an important role in the perceptions of and preferences for looks in opposite sex partners. Aesthetic judgement is highly g-loaded (.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.
IQ and height
Studies have found a weak, but significant 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, or it may be explained by a general fitness factor due to assortative mating regarding fitness.
- Jensen, R. The g Factor: The Science of Mental Ability. 1998. Chaper 6: Biological Correlates of g, pp 157. https://emilkirkegaard.dk/en/wp-content/uploads/The-g-factor-the-science-of-mental-ability-Arthur-R.-Jensen.pdf
- Hapern CT, Joyner K, Udry JR, Suchindran C. 2000. Smart teens don't have sex (or kiss much either). J Adolesc Health. 26(3): 213-25. https://www.ncbi.nlm.nih.gov/pubmed/10706169?dopt