Does Improvability of IQ Mean Intelligence Can Be Equalized?

Dr. Russell T. Warne

Jun 18, 2025

The so-called Flynn effect is leveling off in the West, but Kenya is still on an upward trend, notching 25 points since testing began in the ‘80s. Many impoverished countries have yet to turn this corner [of the Flynn effect stopping]. When they do, we should expect to see a great IQ equalizing. (Chodosh, 2018, p. 9)

Although Chapter 16 encourages us to hold our enthusiasm in check, it is clear from the evidence that I have presented in this book that IQ can improve through environmental interventions. Indeed, the Flynn effect (see Chapter 14) shows that the twentieth century was one big demonstration that improved environments can lead to higher IQ scores. As a result, some people – as demonstrated by the quote at the beginning of the chapter – believe that the changeability of IQ means that IQ can be equalized. While improvability of IQ scores – and intelligence – is possible, it is quite a different matter to make everyone’s intelligence equal.

Does Equalizing Environments Result in Equal IQs?

An extreme example of an attempt to equalize environments occurred after World War II when the Soviet-supported regime in Poland rebuilt the city of Warsaw, almost three-quarters of which had been destroyed. To implement communist ideals, the government built neighborhoods that were as uniform as possible, with homes, apartment buildings, and commercial buildings being similar throughout the city. Social and cultural services were distributed approximately evenly throughout Warsaw, and families were assigned homes so that every neighborhood contained a mixture of people who worked in low-, mid-, and high-prestige occupations. After three decades of this intensive, egalitarian urban planning, a team of scientists administered a non-verbal intelligence test to a large, representative sample of children in the city. The results indicated that the process to equalize the neighborhood environment did nothing to neutralize the positive correlation that IQ had with parental occupational prestige and parental education. As the authors stated, “Despite this social policy of equalization, the association [between parental characteristics and child IQ] persists in a form characteristic of more traditional societies” (Firkowska et al., 1978, p. 1362).

In the Polish study, the similar living conditions and uniform education system were (a) not only unable to eliminate IQ differences, but also (b) incapable of eliminating the correlation between parental socioeconomic status and child IQ. In fact, the correlation between these two values was similar to what is found in capitalist countries (see Chapter 11), and the authors recognized this. The implication is that a massive effort to remake the social and socioeconomic environment of an entire city did little to equalize intelligence. The authorities in post-World War II Poland had far more power to change the environment than any democratic government does, which should make anyone skeptical about the ability of social programs in democratic nations to equalize intelligence.

Another Attempt: Improving the Environment

Perhaps equalizing intelligence is too ambitious. Instead, some people who create environmental interventions have the more modest goal of reducing individual differences in IQ by improving environments. There is some evidence that obtaining this goal is reasonable. For example, Tucker-Drob (2012) found that preschool reduced differences in math and reading skills (though there was no follow-up to determine whether fadeout occurred later). Likewise, educational policies that focus on struggling students lead to greater improvements in these students’ academic performance and reduce overall variability (Lee, 2002). Statistically controlling for important environmental variables like socioeconomic status also reduces IQ differences among individuals (though in the real world the unadjusted differences still exist), which might indicate that reducing socioeconomic differences could reduce IQ differences.

The evidence is clear that providing a more positive environment to people in an unfavorable environment does reduce inequality of intelligence among the population as a whole. On the other hand, giving an intervention or an environmental improvement to the entire population usually does not eliminate intelligence differences because people in both the top and bottom IQ groups experience improvements (Jensen, 1991). In other words, even if environmental changes help people with lower intelligence, the inequality of IQ persists because these changes also help people with higher intelligence. Thus, the best way to reduce individual differences in intelligence or related abilities (e.g., academic skills or cognitive skills) is to provide a beneficial treatment to low-performing individuals and withhold it from high-performing individuals.

Genetics: Why Interventions Do Not Equalize Abilities

Inequality of intelligence stubbornly persists because of one simple fact: IQ scores are partially influenced by genes, as indicated by h2 values greater than zero (see Chapter 11). As a result, environmental interventions do not equalize intelligence in people because the genetic influences still remain. Changing educational programs, improving a family’s socioeconomic status, or making neighborhoods as similar as possible will not equalize people’s intelligence because none of these environmental changes alter the fact that people vary genetically and that those variations cause some of the differences in intelligence. As long as genetic variation exists in humans, so will IQ differences. This is why Chodosh’s (2018, p. 9) prediction of “a great IQ equalizing” is unrealistic. Even if all countries eventually become wealthy, educated, and industrialized (which itself is not guaranteed; see Rindermann, 2018), this would not equalize IQ scores worldwide because genetic differences among humans would still exist.

Table 17.1 shows the estimated variability in IQ that would be observed if all environments were equalized. The variability is measured with the standard deviation (SD), and currently, intelligence tests have a standard deviation of 15 points (as stated in the Introduction). If all environmental influences were eliminated or equalized, then variability would be reduced and intelligence differences would decrease. However, Table 17.1 also shows that this drop in variability is small when h² is high. For example, in a population with heritability of .80 (as is common in studies of adults in wealthy countries), eliminating environmental differences in IQ would only decrease the SD of IQ scores by 10.6%, from 15 points to 13.4 points. If h² is .50, then equalized environments would decrease the SD of IQ scores by 29.3% to 10.6 points. Only for traits with low heritability (for which environments already exert a powerful influence on intelligence differences) do individual differences get substantially reduced if environments are equalized.

Table 17.1 Change in standard deviation (SD) of IQ scores if environments were equalized

Heritability (h2)	SD with environmental influences eliminated	% Reduction in SD
.00	0.0 IQ points	100.0%
.10	4.7 IQ points	68.4%
.20	6.7 IQ points	55.3%
.30	8.2 IQ points	45.2%
.40	9.5 IQ points	36.8%
.50	10.6 IQ points	29.3%
.60	11.6 IQ points	22.5%
.70	12.5 IQ points	16.3%
.80	13.4 IQ points	10.6%
.90	14.2 IQ points	5.1%
1.00	15.0 IQ points	0.0%

It is important to recognize that improving environments for everyone is different from removing environmental differences. Improving environments in general can increase the average IQ score without impacting the importance of genetic and environmental differences in producing relative differences in IQ scores. Chapter 12 had an example of how this could happen if lead levels are improved for a population in order to increase mean IQ without changing the differences in IQ among a population. On the other hand, to remove the influence of environmental differences is the equivalent of giving everyone the same environment. If this occurs, then heritability must increase because the influence of heritability and the influence of environmental differences must add up to 100%. Therefore, if one influence decreases (e.g., environmental differences), then the other gets bigger to compensate. As a result, equalizing environments will not remove the impact of genetic influences at all; it will increase the relative power of genetic influences.

A similar phenomenon seems to happen when environments are improved. Preschoolers in Tucker-Drob’s (2012) study had higher heritability for reading and math scores than similar children who did not attend preschool. Apparently, sending children to the more intellectually stimulating preschool environment allowed their genes to express themselves in ways that increased the genetic influences on math and reading scores. Positive environments seem to allow genetic influences to be most pronounced. Therefore, any efforts to improve the environment for the entire population will probably increase the influence of genetics, because heritability will increase. Ironically, an improved environment may increase the importance of genetic differences among people, which is the exact opposite of the goal of some people who are trying to improve environments.

Equalizing Differences: What It Would Take

Three facts suggest that real-world attempts to equalize intelligence in people will not be successful: (a) the meager results of the Polish attempt to equalize environments, (b) the important influence of genes in creating IQ differences, and (c) the higher heritability in more positive environments. This raises the question of what it would take to equalize intelligence in a population. Reducing all individual differences in any trait (including intelligence) requires eradicating the causes of those differences. I believe there are three ways that this could theoretically happen

One way to equalize intelligence differences would require equalizing everybody genetically and also equalizing environments. Current technology does not permit that level of genetic engineering. Even if it were possible, the result would probably not be sustainable. The temptation to break any pact of genetic equality in order for one’s offspring or one’s country to gain an advantage over others would be too great. The technology that could make people genetically equal would be just as easily used to engineer new genetic inequalities by anyone willing to ignore any agreement to equalize people genetically.

The second option to equalize intelligence would be to change environments so that people who have a genetic predisposition to be smarter would be placed in negative environments and people with genetic disadvantages would receive more beneficial environments (Gottfredson, 2011). In this way environmental advantages would cancel out the genetic disadvantages that predispose some people to a lower IQ, and vice versa – at least in theory. There are two problems with this proposal. First, environmental influences on IQ are strongest in childhood, but as people age, h2 increases, indicating that environmental influences fade in importance (Bouchard, 2014). As a result, a scheme to have environmental and genetic advantages and disadvantages cancel each other out might only be effective in childhood. As people grow older and gain freedom to select their environments, this social engineering would be less effective – perhaps completely ineffective.

And that makes the second problem clear: a plan to place genetically disadvantaged individuals in a positive environment (and genetically advantaged individuals in a negative environment) would require a total loss of freedom that only a massively oppressive regime could carry out. Most (maybe all) children would be taken away from their parents and placed with new families. Precocious individuals would be denied an education or any access to libraries and books. If these measures were ineffective, then more drastic actions might be required: maybe individuals whose intelligence was too high would be given brain injuries to reduce their IQ. This option for eliminating intelligence differences is a horribly dystopian scenario, and it would inflict huge levels of suffering on people. Proposing (let alone implementing) such a program is not feasible.

The final option would be to give everyone such uniformly deprived environments that genes do not have the opportunity to express themselves enough for intelligence differences to develop. This would require denying all people in the population any known positive environmental influences: schooling, access to healthy environments and medical care, sufficient food and nutrition, physical safety, a nurturing caregiver in childhood, etc. This option is unspeakably cruel and would inflict great misery on a population that experienced it. The costs would not only be huge, but the benefits would be meager: even if IQ scores were equalized, they would be equally low, and no industrialized society could function with a population mired in ignorance, disease, and starvation.

No one advocates any of these three methods for equalizing IQ. However, the drastic measures that would probably be required to equalize IQ should show why more modest interventions to eliminate individual differences in intelligence have failed.

Improving Lives, Not Equalizing Them

While improvability of intelligence does not imply equalizability, it is also false that the non-equalizability of intelligence means non-improvability (Gottfredson, 2009). Because feasible options for equalizing IQ are likely to be ineffective, I believe that it is fruitless to worry about eradicating individual differences. A better goal is to improve people’s lives. Sometimes this will result in higher IQ scores (e.g., treating iodine deficiency, discouraging women from drinking alcohol during pregnancy), and sometimes it will not (e.g., providing nutritious meals for children who live in poverty). There are many ways to improve people’s lives, and the best way to do so will depend on a society’s resources, goals, and ethics.

Just as with any intervention, though, it is important to have a realistic understanding of what probably is (or is not) possible, given current knowledge. Two leading scholars from the past, Scarr and Weinberg (1978, p. 36), described the issue well:

Three decades of naive environmentalism have locked most Westerners into wrong-headed assumptions about the limitless malleability of mankind, and programs based on this premise can lead a country into a thicket of unrealistic promises and hopes. The fallacy is the belief that equality of opportunity produces sameness of outcome. Equality of opportunity is a laudable goal for any society. Sameness of outcome is a biological impossibility.

Despite the best efforts of a society, inequality of IQ will happen. Some children will get “left behind,” and some people will not be able to attend college or reap the benefits of high reasoning ability. (Chapter 33 discusses how industrialized societies can adapt to this fact.) On the other hand, lying about intelligence differences and their malleability or equalizability only sets people up for disappointment.

From Chapter 17 of "In the Know: Debunking 35 Myths About Human Intelligence" by Dr. Russell Warne (2020)

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