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Introduction

Hereditarianism is the theory that differences in psychology between individuals and groups have a ‘genetic’ or ‘innate’ (to capture the thought before the ‘gene’ was conceptualized) cause to them—which therefore would explain the hows and whys of, for example, the current social hierarchy. The term ‘racism’ has many referents—and using one of the many definitions of ‘racism’, one could say that the hereditarian theory is racist since it attempts to justify and naturalize the current social hierarchy.

In what I hope is my last word on the IQ/hereditarian debate, I will provide three conceptual arguments against hereditarianism: (1) psychologists don’t ‘measure’ any’thing’ with their psychological tests since there is no object of measurement, no specified measured object, and measurement unit for any specific trait; only physical things can be measured and psychological ‘traits’ are not physical so they cannot be measured (Berka, 1983; Nash, 1990; Garrison, 2009); (2) there is no theory or definition of “intelligence” (Lanz, 2000; Richardson, 2002; Richardson and Norgate, 2015; Richardson, 2017) so there can be no ‘measure’ of it, the example of temperature and thermometers will be briefly mentioned; (3) the logical impossibility of psychophysical reduction entails that mental abilities/psychological traits cannot be genetically inherited/transmitted; and (4) psychological theories are influenced by the current problems/going-on in society as well as society influencing psychological theories. These four objections are lethal to hereditarianism, the final showing that psychology is not an ‘objective science.’

(i) The Berka/Nash measurement objection

The Berka/Nash measurement objection is simply: if there is no specified measured object, object of measurement or measuring unit for the ‘trait’, then no ‘thing’ is truly being ‘measured’ as only physical things can be measured. Nash gives the example of a stick—the stick is the measured object, the length of the stick is the object of measurement (the property being measured) and inches, centimeters etc are the measuring units. Being that the stick is in physical space, its property can be measured—its length. Since psychological traits are not physical (this will also come into play for (ii) as well) nor do they have a physical basis, there can be no ‘measuring’ of psychological traits. Indeed, since scaling is accepted by fiat to be a ‘measure’ of something. This, though, leads to confusion, especially to psychologists.

The most obvious problem with the theory of IQ measurement is that although a scale of items held to test ‘intelligence’ can be constructed, there are no fixed points of reference. If the ice point of water at one atmosphere fixes 276.16 K, what fixes 140 points of IQ? Fellows of the Royal Society? Ordinal scales are perfectly adequate for certain measurements. Moh’s scale of scratch hardness consists of ten fixed points from talc to diamond, and is good enough for certain practical purposes. IQ scales (like attainment test scales) are ordinal scales, but this is not really to the point, for whatever the nature of the scale it could not provide evidence for the property IQ or, therefore, that IQ has been measured. (Nash, 1990: 131)

In first constructing its scales and only then preceding to induce what they ‘measure’ from correlational studies, psychometry has got into the habit of trying to do what cannot be done and doing it the wrong way round anyway. (Nash, 1990: 133)

The fact of the matter is, IQ tests don’t even meet the minimal theory of measurement since there is no—non-circular—definition of what this ‘general cognitive ability’ even is.

(ii) No theory or definition of intelligence

This also goes back to Nash’s critique of IQ (since there can be no non-circular definition of what “IQ tests” purport to measure): There is no theory or definition of intelligence therefore there CAN BE no ‘measure’ of it. Imagine saying that you have measured temperature without a theory behind it. Indeed, I have explained in another article that although IQ-ists like Jensen and Eysenck emphatically state that the ‘measuring’ of ‘intelligence’ with “IQ tests” is “just like” the measuring of temperature with thermometers, this claim fails as there is no physical basis to psychological traits/mental abilities so they, therefore, cannot be measured. If “intelligence” is not like height or weight, then “intelligence”‘ cannot be measured. “Intelligence” is not like height or weight. Therefore, “intelligence” cannot be measured.

We had a theory and definition of temperature and then the measuring tool was constructed to measure our new construct. The construct of temperature was then verified independently of the instrument used to originally measure it, with the thermoscope which then was verified with human sensation. Thus, temperature was verified in a non-circular way. On the other hand, “intelligence tests” are “validated” circularly, if the tests correlate highly with other older tests (like Terman’s Stanford-Binet), it is held that the new test ‘measures’ the construct of ‘intelligence’—even if none of the previous tests have themselves been validated!

Therefore, this too is a problem for IQ-ists—their scale was first constructed (to agree with the social hierarchy, no less; Mensh and Mensh, 1991) and then they set about trying to see what their scales ‘measure’ with correlational studies. But we know that since two things are correlated that doesn’t mean that one causes the other—there could be some unknown third variable causing the relationship or the relationship could be spurious. In any case, this conceptual problem, too, is a problem for the IQ-ist. IQ is nothing like temperature since temperature is an actual physical measure that was verified independently of the instrument constructed to measure the construct in the first place.

Claims of individuals as ‘intelligent’ (whatever that means) or not are descriptive, not explanatory—it is the reflection of one’s current “ability” (used loosely) in relation to their current age norms (Anastasi; Howe, 1997).

(iii) The logical impossibility of psychophysical reduction

I will start this section off with two (a priori) arguments:

Anything that cannot be described in material terms using words that only refer to material properties is immaterial.
The mind cannot be described in material terms using words that only refer to material properties.
Therefore the mind is immaterial; materialism is false.

and

If physicalism is true then all facts can be stated using a physical vocabulary.
But facts about the mind cannot be stated using a physical vocabulary.
So physicalism is false.

(Note that the arguments provided are valid, and I hold them to be sound thus an objector would need to reject then refute a premise.)

Therefore, if all facts cannot be stated using a physical vocabulary and if the mind cannot be described in material terms using words that only refer to material properties, then there can, logically, be no such thing as ‘mental measurement’—no matter what IQ-ists try to tell you.

Different physical systems can give rise to different mental phenomena—what is known as the argument from multiple realizability. Thus, since psychological traits/mental states are multiply realizable, then it is impossible for psychology to reduce to mental kinds to reduce to physical kinds—the mental kind can be realized by multiple physical states. Psychological states are either multiply realizable or they are type identical to the physio-chemical states of the brain. That is a kind of mind-brain identity thesis—that the mind is identical to the states of the brain. Although they are correlated, this does not mean that the mind is the brain or that the mind can be reduced to physio-chemical states, as Putnam’s argument from multiple realizability concludes. If type-physicalism is true, then it must be true that every and all mental properties can be realized in the same exact way. But, empirically, it is highly plausible that mental properties can be realized in multiple ways. Therefore, type-identity theory is false.

Psychophysical laws are laws connnecting mental abilities/psychological traits with physical states. But, as Davidson famously argued in his defense of Anomalous Monism, there can be no such laws linking mental and physical events. There are no mental laws therefore there can be no scientific theory of mental states. Science studies the physical. The mental is not physical. Thus, science cannot study the mental. Indeed, since there are no bridge laws that link the mental and physical and the mental is irreducible to and underdetermined by the physical, it then follows that science cannot study the mental. Therefore, a science of the mind is impossible.

Further note that the claim “IQ is heritable” reduces to “thinking is heritable”, since the main aspect of test-taking is thinking. Thinking is a mental activity which results in a thought. If thinking is a mental activity which results in a thought, then what is a thought? A thought is a mental state of considering a particular idea or answer to a question or committing oneself to an idea or an answer. These mental states are, or are related to, beliefs. When one considers a particular answer to a question, they are paving the way to holding a certain belief. So when they have committed themselves to an answer, they have committed themselves to a new belief. Since beliefs are propositional attitudes, believing p means adopting the belief attitude that p. So, since cognition is thinking, then thinking is a mental process that results in the formation of a propositional belief. Thus, since thinking is related to beliefs and desires (without beliefs and desires we would not be able to think), then thinking (cognition) is irreducible to physical/functional states, meaning that the main aspect of test-taking (thinking) is irreducible to the physical thus physical states don’t explain thinking which means the main aspect of (IQ) test-taking is irreducible to the physical.

(iv) Reflexivity in psychology

In this last section, I will discuss the reflexivity—circularity—problem for psychology. This is important for psychological theorizing since, to its practitioners, psychology is seen to be an ‘objective science.’ If you think about psychology (and science) and how it is practiced, it (they) investigates third-personal, not first-personal, states. Thus, there can be no science of the mind (what psychology purports to be) and psychology can, therefore, not be an ‘objective science’ as the hard sciences are. The ‘knowledge’ that we attain from psychology comes from, obviously, the study of people. As Wade (2010: 5) notes, the knowledge that people and society are the object of study “creates a reflexivity, or circular process of cause and effect, whereby the ‘objects’ of study can and do change their behavior and ideas according to the conclusions that their observers draw about their behavior and ideas.”

It is quite clear that such academic concepts do not arise independently—in the history of psychology, it has been used in an attempt to justify the current social hierarchy of the time (as seen in 1900s America, Germany, and Britain). Psychological theories are influenced by current social goings-on. Thus, it is influenced by the bias of the psychologists in question. “The views, attitudes, and values of psychologists influence the claims they make” (Jones, Elcock, and Tyson, 2011: 29).

… scientific ideas did not develop in a vacuum but rather reflected underlying political or economic trends. 15

The current social context influences the psychological discourse and the psychological discourse influences the current social context. The a priori beliefs that one holds will influence what they choose to study. An obvious example being, hereditarian psychologists who believe there are innate differences in ‘IQ’ (they use ‘IQ’ and ‘intelligence’ interchangeably as if there is an identity relation) will undertake certain studies in order to ‘prove’ that the relationship they believe to be true holds and that there is indeed a biological cause to mental abilities within and between groups and individuals. Do note, however, that we have the data (blacks score lower on IQ tests) and one must then make an interpretation. So we have three possible scenarios: (1) differences in biology cause differences in IQ; (2) differences in experience cause differences in IQ; or (3) the tests are constructed to get the results the IQ-ists want in order to justify the current social hierarchy. Mensh and Mensh (1991) have succinctly argued for (3) while hereditarians argue for (1) and environmentalists argue for (2). While it is indeed true that one’s life experiences can influence their IQ scores, we have seen that it is logically impossible for genes to influence/cause mental abilities/psychological traits.

The only tenable answer is (3). Such relationships, as noted by Mensh and Mensh (1991), Gould (1996), and Garrison (2009), between test scores and the social hierarchy are interpreted by the hereditarian psychologist thusly: (1) our tests measure an innate mental ability; (2) if our tests measure an innate mental ability, then differences in the social hierarchy are due to biology, not environment; (3) thus, environmental differences cannot account for what is innate between individuals so our tests measure innate biological potential for intelligence.

The [IQ] tests do what their construction dictates; they correlate a group’s mental worth with its place in the social hierarchy. (Mensh and Mensh, 1991)

Richards (1997) in his book on racism in the history of psychology, identified 331 psychology articles published between 1909 (the first conceptualization of the ‘gene’, no less) and 1940 which argued for biology as a difference-maker for psychological traits while noting that 176 articles for the ‘environment’ side were published in that same time period.

Note that the racist views of the psychologists in question more than likely influenced their research interests—they set out to ‘prove’ their a priori biases. Indeed, they even modeled their tests after such biases. Tests that were constructed that agreed with their a priori pre-suppositions on who was or was not intelligence was kept whereas those that did not agree with those notions were thrown out (as noted by Hilliard, 2012). This is just as Jones, Elcock, and Tyson (2011: 67) note with the ‘positive manifold’ (‘general intelligence’):

Subtests within a battery of intelligence tests are included n the basis of them showing a substantial correlation with the test as a whole, and tests which do not show such correlations are excluded.

From this, it directly follows that psychometry (and psychology) are not sciences and do not ‘measure’ anything (returning to (i) above). What psychometrics (and psychology) do is attempt to use their biased tests in order to sort individuals into where they ‘belong’ on the social hierarchy. Standardized testing (IQ tests were one of the first standardized tests, along with the SAT)—and by proxy psychometrics—is NOT a form of measurement. The hierarchy that the tests ‘find’ is presupposed to exist and then constructed into existence using the test to ‘prove’ their biases ‘right.’

Indeed, Hilliard (2012) noted that in South Africa in the 1950s that there was a 15-point difference in IQ between two white cultural groups. Rather than fan flames of political tension between the groups, the test was changed in order to eliminate the difference between the two groups. The same, she notes, was the case regarding IQ differences between men and women—Terman eliminated such differences by picking and choosing certain items that favored one group and balanced them out so that they scored near-equally. These are two great examples from the 20th century that demonstrate the reflexivity in psychology—how one’s a priori biases influence what they study and the types of conclusions they draw from data.

Psychology, at least when it comes to racial differences in ‘IQ’, is being used to confirm pre-existing prejudices and not find any ‘new objective facts.’ “… psychology [puts] a scientific gloss on the accepted social wisdom of the day” (Christian, 2008: 5). This can be seen with a reading into the history of “IQ tests” themselves. The point is, that psychology and society influence each other in a reflexive—circular—manner. Thus, psychology is not and cannot be an ‘objective science’ and when it comes to ‘IQ’ the biases that led to the bringing of the tests to America and concurrently social policy are still—albeit implicitly—believed today.

Psychology originally developed in the US in the 19th century in order to attempt to fix societal problems—there needed to be a science of the mind and psychology purported to be just that. They, thusly, needed a science of ‘human nature’, and it was for this reason that psychology developed in the US. The first US psychologists were trained in Germany and then returned to the US and developed an American psychology. Though, do note that in Germany psychology was seen as the science of the mind while in America it would then turn out to be the science of behavior (Jones, Elcock, and Tyson, 2011). This also does speak to the eugenic views held by certain IQ-ists in the 20th and into the 21st century.

In Nazi Germany, Jewish psychologists were purged since their views did not line-up with the Nazi regime.

Psychology appealed to the Nazi Party for two reasons: because psychological theory could be used to support Nazi ideology, and because psychology could be applied in service to the state apparatus. Those psychologists who remained adapted their theories to suit Nazi ideology, and developed theories that demonstrated the necessary inferiority of non-Aryan groups (Jones and Elcock, 2001). These helped to justify actions by the state in discriminating against, and ultimately attempting to eradicate, thse other groups. (Jones, Elcock, and Tyson (2011: 38-39)

These examples show that psychology is influenced by society but also that society influences psychological theorizing. Clearly, what psychologists choose to study, since society influences psychology, is a reflection of a society’s social concerns. In the case of IQ, crime, etc, the psychologist attempts to naturalize and biologicize such differences in order to explain them as ‘innate’ or ‘genetic’. The rise of IQ tests in America, too, also coincided with the worry that ‘national intelligence’ was declining and so, the IQ test would need to be used to ‘screen’ prospective immigrants. (See Richardson, 2011 for an in-depth consideration on the tests and conditions that the testees were exposed to on Ellis Island; also see Gould, 1996.)

Conclusion

(i) The Berka/Nash measurement objection is one of the most lethal arguments for IQ-ists. If they cannot state the specified measured object, the object of measurement, and the measuring unit for IQ then they cannot say that any’thing’ is being ‘measured’ by ‘IQ tests.’ This then brings us to (ii). Since there is no theory or definition of what is being ‘measured’, and if the tests were constructed first before the theory, then there will necessarily be a built-in bias to what is being ‘measured’ (namely, so-called ‘innnate mental potential’). (iii) Since it is logically impossible for psychology to reduce to physical structure, and since all facts cannot be stated using a physical vocabulary nor can the mind be described using material terms that only refer to material properties, then this is another blow to the claim that psychology is an ‘objective science’ and that some’thing’ is being ‘measured’ by their tests (constructed to agree with their a priori biases). And (iv) The bias that is inherent in psychology (for both the right and the left) influences the practitioners’ theorizing and how they interpret data. Society has influenced psychology (and psychology has influenced the society) and we only need to look at America and Nazi Germany in the 20th century to see that this holds.

The relationship between psychology and society is inseparable—it is a truism that what psychologists choose to study and how and why they formulate their conclusions will be influenced by the biases they already hold about society and how and why it is the way it is. For these reasons, psychology/psychometry are not ‘sciences’ and hereditarianism is not a logically sound position. Hereditarianism, then, stays what it was when it was formulated—a racist theory that attempts to bilogicize and justify the current social hierarchy. Thus, one should not accept that psychologists ‘measure’ any’thing’ with their tests; one should not accept the claim that mental abilities can be genetically transmitted/inherited; one should not accept the claim that psychology is an objective ‘science’ due to the reflexive relationship between psychology and society.

The arguments given show why hereditarianism should be abandoned—it is not a scientific theory, it just attempts to naturalize biological inequalities between individuals and groups (Mensh and Mensh, 1991; Gould, 1996; Garrison, 2009). Psychometrics (what hereditarians use to attempt to justify their claims) is, then, nothing more than a political ring.

1800 words

The history of standardized testing—including IQ testing—has a contentious history. What causes score distributions between groups of people? I stated at least four reasons why there is a test gap:

(1) Differences in genes cause differences in IQ scores;

(2) Differences in environment cause differences in IQ scores;

(3) A combination of genes and environment cause differences in IQ scores; and

(4) Differences in IQ scores are built into the test based on the test constructors’ prior biases.

I hold to (4) since, as I have noted, the hereditarian-environmentalist debate is frivolous. There is, as I have been saying for years now, no agreed-upon definition of ‘intelligence’, since there are such disparate answers from the ‘experts’ (Lanz, 2000; Richardson, 2002).

For the lack of such a definition only reflects the fact that there is no worked-out theory of intelligence. Having a successful definition of intelligence without a corresponding theory would be like having a building without foundations. This lack of theory is also responsible for the lack of some principled regimentation of the very many uses the word ‘intelligence’ and its cognates are put to. Tao many questions concerning intelligence are still open, too many answers controversial. Consider a few examples of rather basic questions: Does ‘intelligence’ name some entity which underlies and explains certain classes of performances1, or is the word ‘intelligence’ only sort of a shorthand-description for ‘being good at a couple of tasks or tests’ (typically those used in IQ tests)? In other words: Is ‘intelligence’ primarily a descriptive or also an explanatorily useful term? Is there really something like intelligence or are there only different individual abilities (compare Deese 1993)? Or should we turn our backs on the noun ‘intelligence’ and focus on the adverb ‘intelligently’, used to characterize certain classes of behaviors? (Lanz, 2000: 20)

Nash (1990: 133-4) writes:

Always since there are just a series of tasks of one sort or another on which performance can be ranked and correlated with other performances. Some performances are defined as ‘cognitive performances’ and other performances as ‘attainment performances’ on essentially arbitrary, common sense grounds. Then, since ‘cognitive performances’ require ‘ability’ they are said to measure that ‘ability’. And, obviously, the more ‘cognitive ability’ an individual posesses the more that individual can acheive. These procedures can provide no evidence that IQ is or can be measured, and it is rather besides the point to look for any, since that IQ is a metric property is a fundamental assumption of IQ theory. It is imposible that any ‘evidence’ could be produced by such procedures. A standardised test score (whether on tests designated as IQ or attainment tests) obtained by an individual indicates the relative standing of that individual. A score lies within the top ten perent or bottom half, or whatever, of those  gained by the standardisation group. None of this demonstrates measurement of any property. People may be rank ordered by their telephone numbers but that would not indicate measurement of anything. IQ theory must demonstrate not that it has ranked people according to some performance (that requires no demonstration) but that they are ranked according to some real property revealed by that performance. If the test is an IQ test the property is IQ — by definition — and there can in consequence be no evidence dependent on measurement procedures for hypothesising its existence. The question is one of theory and meaning rather than one of technique. It is impossible to provide a satisfactory, that is non-circular, definition of the supposed ‘general cognitive ability’ IQ tests attempt to measure and without that definition IQ theory fails to meet the minimal conditions of measurement.

These is similar to Mary Midgley’s critique of ‘intelligence’ in her last book before her death What Is Philosophy For? (Midgley, 2018). The ‘definitions’ of ‘intelligence’ and, along with it, its ‘measurement’ have never been satisfactory. Haier (2016: 24) refers to Gottfredson’s ‘definition’ of ‘intelligence, stating that ‘intelligence’ is a ‘general mental ability.’ But if that is the case, that it is a ‘general mental ability’ (g) then ‘intelligence’ does not exist because ‘g’ does not exist as a property in the brain. Lanz’s (2000) critique is also like Howe’s (1988; 1997) that ‘intelligence’ is a descriptive, not explanatory, term.

Now that the concept of ‘intelligence’ has been covered, let’s turn to race and test bias.

Test items are biased when they have different psychological meanings across cultures (He and van de Vijver 2012: 7). If they have different meanings across cultures, then the tests will not reflect the same ‘ability’ between cultures. Being exposed to the knowledge—and correct usage of it—on a test is imperative for performance. For if one is not exposed to the content on the test, how are they expected to do well if they do not know the content? Indeed, there is much evidence that minority groups are not acculturated to the items on the test (Manly et al, 1997; Ryan et al, 2005; Boone et al, 2007). This is what IQ tests measure: acculturation to the the tests’ constructors, school cirriculum and school teachers—aspects of white, middle-class culture (Richardson, 1998). Ryan et al (2005) found that reading and and educational level, not race or ethnicity, was related to worse performance on psychological tests.

Serpell et al (2006) took 149 white and black fourth-graders and randomly assigned them to ethnically homogeneous groups of three, working on a motion task on a computer. Both blacks and whites learned equally well, but the transfer outcomes were better for blacks than for whites.

Helms (1992) claims that standardized tests are “Eurocentric”, which is “a perceptual set in which European and/ or European American values, customs, traditions and characteristics are used as exclusive standards against which people and events in the world are evaluated and perceived.” In her conclusion, she stated that “Acculturation
and assimilation to White Euro-American culture should enhance one’s performance on currently existing cognitive ability tests” (Helms, 1992: 1098). There just so happens to be evidence for this (along with the the studies referenced above).

Fagan and Holland (2002) showed that when exposure to different kinds of information was required, whites did better than blacks but when it was based on generally available knowledge, there was no difference between the groups. Fagan and Holland (2007) asked whites and blacks to solve problems found on usual IQ-type tests (e.g., standardized tests). Half of the items were solvable on the basis of available information, but the other items were solveable only on the basis of having acquired previous knowledge, which indicated test bais (Fagan and Holland, 2007). They, again, showed that when knowledge is equalized, so are IQ scores. Thus, cultural differences in information acquisition explain IQ scores. “There is no distinction between crassly biased IQ test items and those that appear to be non-biased” (Mensh and Mensh, 1991). This is because each item is chosen because it agrees with the distribution that the test constructors presuppose (Simon, 1997).

How do the neuropsychological studies referenced above along with Fagan and Holland’s studies show that test bias—and, along with it test construction—is built into the test which causes the distribution of the scores observed? Simple: Since the test constructors come from a higher social class, and the items chosen for inclusion on the test are more likely to be found in certain cultural groups than others, it follows that the reason for lower scores was that they were not exposed to the culturally-specific knowledge used on the test (Richardson, 2002; Hilliard, 2012).

The [IQ] tests do what their construction dictates; they correlate a group’s mental worth with its place in the social hierarchy. (Mensh and Mensh, 1991)

This is very easily seen with how such tests are constructed. The biases go back to the beginning of standardized testing—the first one being the SAT. The tests’ constructors had an idea of who was or was not ‘intelligent’ and so constructed the tests to show what they already ‘knew.’

…as one delves further … into test construction, one finds a maze of arbitrary steps taken to ensure that the items selected — the surrogates of intelligence — will rank children of different classes in conformity with a mental hierarchy that is presupposed to exist. (Mensh and Mensh, 1991)

Garrison (2009: 5) states that standardized tests “exist to assess social function” and that “Standardized testing—or the theory and practice known as “psychometrics” … is not a form of measurment.” The same way tests were constructed in the 1900s is the same way they are constructed today—with arbitrary items and a presuppossed mental hiearchy which then become baked into the tests by virtue of how they are constructed.

IQ-ists like to say that certain genes are associated with high intelligence (using their GWASes), but what could the argument possibly be that would show that variation in SNPs would cause variation in ‘intelligence’? What would a theory of that look like? How is the hereditarian hypothesis not a just-so story? Such tests were created to justify the hierarchies in society, the tests were constructed to give the results that they get. So, I don’t see how genetic ‘explanations’ are not just-so stories.

1 Blacks and whites are different cultural groups.

2 If (1), then they will have different experiences by virtue of being different cultural groups.is

3 So blacks and whites, being different cultural groups, will score differently on tests of ability, since they are exposed to different knowledge structures due to their different cultures and so, all tests of ability are culture-bound. Knowledge, Culture, Logic, and IQ

Rushton and Jensen (2005) claim that the evidence they review over the past 30 years of IQ testing points to a ‘genetic component’ to the black-white IQ gap, relying on the flawed Minnesota study of twins “reared apart” (Joseph, 2018)—among other methods—to generate heritability estimates and state that “The new evidence reviewed here points to some genetic component in Black–White differences in mean IQ.” The concept of heritability, however, is a flawed metric (Bailey, 1997; Schonemann, 1997; Guo, 2000; Moore, 2002; Rose, 2006; Schneider, 2007; Charney, 2012, 2013; Burt and Simons, 2014; Panofsky, 2014; Joseph et al, 2015; Moore and Shenk, 2016; Panofsky, 2016; Richardson, 2017). That G and E interact means that we cannot tease out “percentages” of nature and nurture’s “contribution” to a “trait.” So, one cannot point to heritability estimates as if they point to a “genetic cause” of the score gap between blacks and whites. Further note that the gap has closed in recent years (Dickens and Flynn, 2006; Smith, 2018).

And now, here is another argument based on the differing experiences that cultural groups experience which then explains IQ score differences (eg Mensh and Mensh, 1991; Manly et al, 1997; Kwate, 2001; Fagan and Holland, 2002, 2007; Cole, 2004; Ryan et al, 2005; Boone et al, 2007; Au, 2008; Hilliard, 2012; Au, 2013).

(1) If children of different class levels have experiences of different kinds with different material; and
(2) if IQ tests draw a disproportionate amount of test items from the higher classes; then
(c) higher class children should have higher scores than lower-class children.