Metafact Review: Human Intelligence
Artificial Intelligence has seen a surge in popular interest ever since ChatGPT made it easier for people to ask the internet questions. Our understanding of Human Intelligence seems to have taken a back-seat in recent times. So we gathered more than 30 of the worlds top researchers in neuroscience, education and intelligence to share the facts about Human Intelligence. From IQ tests, Nature vs Nurture to brain games and even whether liberals are more intelligent, this review created lots of debate amongst experts and subscribers when we published it. Here’s what we found…
Genes play a big role in determining your intelligence - from 50-80% in the later part of life.
But genes aren't determinative. Education and environment is still critical for children.
IQ tests are one way to measure intelligence. In general, they're fairly accurate at predicting certain outcomes like grades and general success in life.
Brain games don't boost your intelligence.
Creativity declines from middle age(~44). But your general knowledge and vocabulary will likely increase over your life.
Emotional intelligence is important. Difficult to test for but certain people are better at reading others' emotions.
Is intelligence nature or nurture?
In 2014, the famous podcaster Joe Rogan posted a YouTube video in which he discussed his experience taking a “brain supplement” called Alpha BRAIN. “My ability to form sentences seemed smoother,” he claimed. “It seemed like I had an extra gear, like I was one step ahead in conversations … It’s 100% legit.”
But is it 100% legit? Fire up a YouTube channel or a podcast, and it’s not uncommon to hear all sorts of host-read advertisements for brain pills that promise to boost performance and increase intelligence. Peruse your smartphone’s app store, and you’ll find any number of apps claiming they will train your brain to be smarter. It’s not until you read the small print on many of these products that you’ll find some disclaimer that they haven’t been tested or approved by any regulatory bodies.
Humans are fascinated by intelligence. We venerate the geniuses in our society while attaching pejorative terms -- moron, idiot, nincompoop -- to those we perceive as less intelligent. Most of all, we’re obsessed with becoming smarter and more knowledgeable.
Is it possible to increase your intelligence? How much is it determined by genetics? Does it decline with age? And what about the more nebulous concept of “emotional intelligence”? Does it really exist?
Those are just some of the questions we’re answering in this month’s Metafact Review. Buckle in, aspiring Einstein, it’s time to consult the experts.
98: Average IQ score in USA
102: Average IQ for college undergraduates
160: Estimated IQ score of Albert Einstein
73: IQ falsely reported for Donald Trump
26%: Of American adults take at least one supplement for brain health
$8,600,000,000: Amount spent globally on brain health supplements in 2022
1905: First intelligence test developed called the Binet-Simon Scale
3.13 sec: Amount of time taken to solve a Rubick’s cube by world record holder
25: Age at which the brain is said to be fully developed
1964: Year the term “emotional intelligence” was first used in a paper
Where does intelligence come from?
Humans have attempted to gauge each other’s intelligence going back hundreds of years. One of the first people to research intelligence was Englishman Sir Francis Galton in the 1800s. He set up a lab to measure noblemen's physical characteristics, testing their reaction-time and other sensory attributes. Galton pioneered quantitative approaches to measure intelligence and coined the phrase 'Nature vs Nurture' in 1874 - a topic that continues to spark immense debate today.
Charles Spearman, an English psychologist noticed that students grades were similar across a range of diverse subjects. In 1904 he proposed the concept of 'General Intelligence' in which each of us have a single underlining 'factor' (g) for mental and cognitive abilities that could be measured.
Meanwhile William Stern, a German psychologist, came up with the idea of taking someone’s intelligence and comparing it to the average intelligence of people of the same age. He called this the “intelligence quotient,” i.e., IQ.
At around this same time, psychologists Alfred Binet and Théodore Simon were developing intelligence tests for children. By the 1920s, these tests had become standardized, and soon IQ tests were considered a reliable way to measure a person’s intelligence.
But even from the very beginning, psychologists considered IQ tests to be heavily flawed. That included Stern, the very person who coined the term. “Under all conditions, human beings are and remain the centers of their own psychological life and their own worth,” he wrote in 1933. “In other words, they remain persons, even when they are studied and treated from an external perspective with respect to others’ goals.”
In 1987, psychologist Raymond Cattell published a book that challenge the prevailing idea there was an underlining single factor defining general intelligence. His suggested intelligence to be split into between structured learning and creative learning, sometimes known as Crystallised Intelligence and Fluid Intelligence.
Fluid Intelligence is the ability to use reasoning to solve new problems without reference to pre-existing knowledge. Crystallized Intelligence is the ability to use knowledge previously acquired through education and experience. Metafact experts refer to these terms often - so it's important to understand what they mean..
Are IQ scores a good predictor of general intelligence?
Ever since the IQ test was invented, people have debated how good it is at actually determining a person’s intelligence. Critics have pointed out that a person’s socioeconomic status and other environmental factors can strongly influence their IQ score, leaving one to wonder whether it truly measures innate intelligence.
Metafact experts largely agree that IQ is a good predictor of general intelligence, but with plenty of caveats. “The real problem is that general intelligence as it has traditionally been defined is not so general,” wrote Robert Sternberg, and expert from Cornell University. “It does not take into account creative intelligence, practical intelligence (common sense), emotional intelligence, social intelligence, or wise uses of intelligence.” Sternberg went on to criticize our overreliance on standardized testing as a proxy of potential, arguing that “these tests do NOT measure our skills in solving important life problems.”
Whether you think IQ scores predicts intelligence will rely largely on what you think qualifies as “intelligence.” “It is reasonable to expect that more intelligent individuals will obtain more education, achieve better grades, have higher incomes, be healthier, happier, attain higher social status, be less likely to develop a drug addiction, and be generally more effective in their chosen occupations,” wrote Louis Matzel, and expert from Rutgers University. “So the question is, does an IQ test that is administered to a young child predict these later life outcomes that we believe are indicative of intelligence. The answer to this question is an overwhelming ‘yes.’ IQ tests have enormous predictive capacity.”
Is intelligence genetic?
As mentioned, it’s been shown that environmental factors do play a role in determining a person’s IQ. And yet we also widely perceive intelligence as something a person is born with. So what role do genes play in determining a person’s intelligence, and how much is it affected by outside, real-world factors like family income, education, and family upbringing?
Metafact experts unanimously agree that intelligence is heavily influenced by genetics and hereditary, but only to a certain extent. “There is a tremendous amount of empirical research clearly showing that intelligence is hereditary,” wrote Dimitri van der Linden, and expert from Erasmus University Rotterdam. “The estimates range somewhere between .50 to .80 (and are likely closer towards the latter).” He and others pointed to twin and adoption studies, the latter showing that parents’ are more likely to have similar IQs to their biological children compared to children they’ve adopted.
Genetic influence on intelligence actually increases with age. “Children adopted at very young ages resemble their adoptive parents in terms of IQ test scores when they are children (i.e., age 5 and younger)" wrote psychologist Nicholas Grahame from Indiana University. "As they grow older, though, they increasingly resemble their biological parents. By the time these children are 16 or so, about 70 to 80% of the differences among individuals can be chalked up to their biological parents' genes, rather than the environment in which they were raised”.
Despite the importance of genes, "they aren't determinative" writes Louis Matzel from Rutgers University, as they "interact with the environment to determine the ultimate level of expression".
Small genetic dispositions can be switched on or off in diverse nurturing environments. "This is why estimates of the heritability of intelligence (as might be obtained from studies of twins) are higher in diverse environments where vast cognitive opportunities exist, and are lower in restricted environments where individuals can’t select cognitive challenges that are appropriate for their abilities. Thus while intelligence is highly heritable, the pure role of genes (absent appropriate environments and opportunities) is probably much lower than these estimates would suggest" Dr Matzel writes.
Vittorio Daniele, an expert from University Magna Graecia, also points out the interplay between genes and environment aren’t mutually exclusive, since “genes expression depends on environment. It is recognised, for example, that extreme poverty and deprivation in infancy negatively impact on individuals’ cognitive abilities."
Is intelligence fixed?
So if intelligence is subject to environmental factors, does that mean there are actually ways to alter it? Scour YouTube and the dietary supplement aisles of your local pharmacy and you’ll find all sorts of products and exercises that will supposedly “boost” your brain activity and IQ. But can the average person take steps to actually improve their own intelligence?
“Intelligence is definitely not fixed,” wrote Andreas Demetriou, an expert University of Nicosia. “In the general population, intelligence increased by about 3 IQ points every in every decade over the 20th century (the phenomenon known as the Flynn effect). Also, intelligence increases by about 2-4 IQ points for every additional school year.” The reason for this is that the brain, itself, is very flexible. “The brain is neuroplastic and keeps changing,” argued Gavin Brown, an expert from University of Auckland. “Stimulus from environments which requires flexibility in processing and exploitation of schematised structures keeps the brain active forming new paths.”
That being said, training exercises focused on boosting intelligence haven’t produced many longterm benefits, at least in controlled studies. “Under some controlled laboratory conditions, various types of cognitive training can have beneficial effects on IQ, but even in these cases, the effects are small (and sometimes non-existent) and always appear to dissipate upon completion of training,” wrote Louis Matzel, an expert from Rutgers University. Davide Piffer pointed to several meta analysis showing that intelligence training doesn’t work. “It's possible to boost only specific cognitive abilities that are similar to the trained task, via near-transfer effects.”
Of course, the biggest boost to intelligence often comes from formal education, which could be considered a form of training. “Studies have been shown that more schooling is causally related to increases in intelligence,” wrote Robert Sternberg, an expert from Cornell University. “This makes sense, as schools--at least, reasonably good ones--exercise one's mind and one's brain.”
Is there a correlation between grades and intelligence?
Given the role education can play in boosting intelligence, does that mean grades are a good indicator of intelligence?
To a certain extent, yes. “The 2007 paper by Deary et al examining the relationship between academic grades and measured intelligence among a sample of 70,000 Scottish secondary students reported a strong correlation of 0.81,” wrote Michael O'Connell, an expert from University College Dublin. “So overall, there is consistent evidence of a moderate to strong correlation between academic grades and measured intelligence.”
That’s not to say there aren’t caveats and exceptions. “Culture, learning disabilities, and even gender may play a major role in predicting academic grades in various settings on one hand,” wrote Leehu Zysberg, an expert from Gordon College. “While on the other - intelligence measures are deeply biased by the very same factors.”
Other Metafact experts were more skeptical of the relationship between grades and intelligence. “The relation between the intelligence and grades is only probabilistic and it depends on many other influences, like social status, income, race, and stereotypes,” wrote Hynek Cígler, an expert from Masaryk University. “If you cannot spend a lot of time studying, or if the study is not valued in your family, you obviously wouldn't have good grades. On the other hand, grades are also dependent on many other traits, like your motivation, conscientiousness etc. Even if you are not really smart, with a huge motivation you can learn a lot and be ‘excellent student.’” Gavin Brown from University of Auckland put it in even simpler terms: smart kids do dumb things (e.g., drugs, not attend, don't try, etc.).”
Do brain games work?
Fire up your smartphone’s app store and you’ll find any number of “brain training” games that claim to make you smarter. But there is any scientific evidence that they actually work?
Not really. “Meta analytic reviews of the empirical literature indicate either tiny or absent gains,” wrote Nachshon Meiran, an expert from Ben-Gurion University of the Negev. “In my opinion, given what we know, it is unfair (or worse) to promise otherwise.”
To a certain extent, these games do train your brain, but this doesn’t mean they make you smarter in any sense of the word. On the whole ... we find that these games only improve the task you are training on, they don't yield general benefits,” wrote Michael Thomas, an expert from Birkbeck, University of London.
The same can be said for these games’ ability to stave off dementia in old age. “I find dementia severity and dementia risk to be specifically related to ‘delta,’ an aspect of general intelligence (‘g’),” wrote Donald R Royall, an expert from University of Texas Health Science Center at San Antonio. “Domain-specific cognitive performance is ‘orthogonal’ (unrelated) to g and delta. While training may improve domain-specific cognitive performance, it is unlikely to be having effects on intelligence unless it generalizes to ALL cognitive domains (and may even other brain-related functions). We're far short of that.”
Does IQ decrease with age?
There are a lot of fears associated with getting older, chief among them is cognitive decline. Any person who’s had a grandparent suffering from dementia how their own cognitive abilities will fare as they age. Is it a rule of nature that intelligence will decline as you age?
Our Metafact experts were torn on this subject. Partly this had to do with the fact that it’s hard to create a controlled, apples-to-apples comparison between age group IQs. For example, younger people today are much more likely to go to college, which has been shown to boost IQ, so you can’t just compare the intelligence of a group of 30-year-olds to a group of 70-year-olds. Alan S. Kaufman, an expert from Yale University, conducted experiments that controlled for these factors, and he found declines in crystallized intelligence and fluid intelligence. Here are his findings:
Average crystalized intelligence per age group:
Ages 20-24: 98 IQ
Ages 35-44: 101 IQ
Ages 45-54: 100 IQ
Ages 55-64: 98 IQ
Ages 65-69: 96 IQ
Ages 70-74: 93 IQ
Ages 75+: 88 IQ
The drop is even more precipitous for average fluid intelligence:
Ages 20-24: 100 IQ
Ages 25-34: 99 IQ
Ages 35-44: 96
Ages 45-54: 91 IQ
Ages 55-64: 86 IQ
Ages 65-69: 83 IQ
Ages 70-74: 79 IQ
Ages 75+: 72 IQ
Other experts argue that aging alone isn’t what causes intelligence decline. “An important characteristic of genetics and early life factors is that they don't tend to change as we age,” wrote Ian Silver, an expert from University of Cincinnati. “As such, if approximately 77-79 percent of intelligence is influenced by factors that don't change as we age, it is unlikely for our level of intelligence to decrease as we age. Negative environmental stimuli (e.g., head trauma) and serious diseases, however, can result in declines in general intelligence. The influence of these factors can correlate with age but aging alone does not influence intelligence.”
Michael Thomas, an expert from Birkbeck, University of London, argued that there are tradeoffs to getting older, with some forms of intelligence improving while others decline. “The fastest response times you will ever have are in your mid-twenties, but (so long as you don't develop dementia), your knowledge of vocabulary will increase throughout your life. Into your late sixties, most cognitive skills relying on things you have learned (so-called crystalised knowledge) either increase or are pretty resilient. The speed with which you can do things can decline.”
Is there scientific evidence for emotional intelligence?
While general intelligence is well-understood, some psychologists have argued for the existence of “emotional intelligence.” One online dictionary defines it as “the capacity to be aware of, control, and express one's emotions, and to handle interpersonal relationships judiciously and empathetically.” In other words, how good are you at reading others’ emotions and moderating your own emotions accordingly to get a desired response?
Metafact experts were mostly in agreement that emotional intelligence exists, though still in need of further study. “Emotional intelligence is hard to measure,” wrote Andrew M Lane, an expert from University of Wolverhampton. “Can people report on their inner knowledge? if you have poor emotional intelligence, you won’t know how good you are but might recognize that being good in emotional intelligence is desirable - because questionnaires are relatively easy to guess what is being assessed.”
Some scientists have attempted to study whether higher emotional intelligence results in any measurable impacts to quality of life. “My research ... found that increased Emotional Intelligence (EI) has a beneficial effect in terms of current depression status,” wrote Sandra J Lloyd, an expert from Northcentral University. “The study indicated that for every 1-point increased in the EQ scaled score, the risk of depression decreased by 5%. This is a highly significant result, as this provides clear evidence that; emotional intelligence and depression are strongly related in the older adult population.”
A crucial flaw with many of these studies, however, is that they rely too heavily on subjective data. “A huge amount of research just used self-report questionnaires and correlated them to other attributes (like depression, life success etc.), but it did not focus on the nature of E.I,” wrote Hynek Cígler, an expert from Masaryk University.
Is it possible to boost your intelligence by training? Education - yes. Brain games - no.
Is intelligence negatively correlated with religious belief? Seems so- but that doesn't imply causation.
Are smart people more liberal? Apparently.
Does music make kids smarter? Smarter kids tend to take music lessons but the evidence for the other causal direction is extremely weak.
Are IQ levels in decline? Maybe.
On average, do men and women differ cognitively?
Unlikely writes Michael Thomas, a neuroscientist from Birbeck, University of London:
Boys and girls don't differ on mathematics skills. Yet these days it is widely recognised that women have much lower representation in Science Technology Engineering and Maths (STEM) occupations. This tells us cultural differences are at work. Any two groups of adults are going to differ if they have different levels of training on some activity. But the differences in cognitive abilities between the genders in children are very small, and when found, they are often not replicated in other studies.
One scientist analysed data from around seven million people looking at gender differences across a range of activities from talking to throwing (Shibley-Hyde, 2005). She found that over three quarters of the studies showed gender differences to be small or almost absent. Even where small differences are found, the much more salient pattern is of great overlap between the distributions of performance. That is, any individual boy will probably do better than lots of girls, and any individual girl will probably do better than lots of boys.
So while there may be some differences between how girls and boys think, those differences are smaller than once thought – and much smaller than the amount of overlap between boys and girls.