2000 words

Introduction

The hereditarian hypothesis posits that genetic/biological factors are responsible for IQ (“intelligence”) and other psychological traits. The claim is basically, IQ is heritable. It is heritable on the basis of twin, family and adoption studies, along with results from GCTA, GWAS and other newer tools that were created in order to lend credence to the twin, family and adoption estimates.

I have distinguished before between what I call “psychological hereditarianism” and “racial hereditarianism.” In this article, I will distinguish between the two more, and while psychological hereditarianism isnt necessarily racist, it can be used for racist aims.

Psychological hereditarianism

Psychological hereditarianism is the belief that psychological differences between people are due largely to genetic or biological factors rather than environmental ones. Claims such as this have been coming from twin studies for decades, and it has been commonly said that such studies have proven that aspects of our psychological constitution are genetically heritable, that is genetically transmitted.

Four kinds of studies exist which lend credence to psychological hereditarianism—family studies, twin studies, adoption studies, and GWAS.

Family studies

Family studies examine the similarities in individuals of the same family when it comes to their cognitive abilities (scores on IQ tests). These studies show that those who share more genes have similar scores than those who don’t. To the hereditarian, this is evidence for their hypothesis that genetic factors contribute to psychological traits and differences in them. Correlations are used to measure the strength of the relationship. An expected value of 50 percent (.5 correlation) between siblings is expected, as they share half of their genes. The correlation that is expected between unrelated individuals is 0, since they presumably don’t share genes (that is, they’re not from the same family).

However, there is one huge issue for family studies—environmental confounding. While people in the same families of course share the same genes, they also share the same environments. So family studies can’t be used as evidence for the psychological hereditarian hypothesis. Behavioral geneticists agree that these studies can’t be used for the genetic hypothesis for psychological traits, but they disagree with the implications of this claim for the next thing I will discuss.

Twin studies

Twin studies again use the correlation coefficient and compare twins raised together or “apart”, to then argue that genes play a substantial role in the etiology of psychological traits like “IQ.” These studies have found that identical twins have more similar cognitive abilities than fraternal twins, which to the twin researchers points to the conclusion that genetic factors contribute to substantially to psychological traits like IQ and other traits. However, the main limitation of such studies comes down to twins reared together. It is assumed that identical and fraternal twins share equally similar environments. This claim, as admitted by twin researchers themselves, is false (Joseph, 2014; Joseph et al, 2015). They then pivot to two arguments—Argument A and Argument B (Joseph et al, 2015)—but A is merely circular and B needs to be shown to be true by twin researchers, that is, they need to rule out and identify trait-relevant factors.

Limitations of twin studies include: not being generalizable to the general population; they’re based on many of the same (false) assumptions that were originally formulated on the 1920s at the advent of twin studies; the findings are misunderstood and blown out of proportion; they lead to volunteer/recruitment bias; and it doesn’t allow the disentangling of G and E since they interact (Sahu and Prasuna, 2016). The “advantages” of these studies aren’t even advantages, since it is conceptually impossible to tease out the relative contributions of G and E to a trait. Nevertheless, twin studies don’t show that psychological hereditarianism is true, and perhaps the most famous twin study of all—the MISTRA—hid the data of its fraternal twins (the controls). Joseph (2022) has an in depth critique of the MISTRA and why conclusions from it should be outright rejected.

Adoption studies

The issues with adoption studies are large, as large as the issues with twin studies. Assignment of adoptees to homes isn’t random, they look for homes that are closer to the homes of the biological mother. This restriction of range reduces the correlation between the adopted children and adopted parent. Adoptees also experience the womb of their biological mother’s (obviously). The adoptive parents are also given information about the adoptee’s family, and this along with conscious and unconscious treatment of the adoptee may help in making the adopted child different (see Richardson and Norgate, 2006; Moore, 2006; Joseph, 2014). Basically, the additive gene model is false, and adoptions don’t simulate a random design.

GWAS

The larger issue at hand here is how the aforementioned have been used to search the genome for the genes that lead to the high heritabilities of IQ. This has then led to the creation of polygenic scores. These studies examine the association between genes and IQ in large samples of individuals. These studies compare the genomes of people who have a certain trait, and they then look for correlations between the genes and the traits in that population. GWASs may miss rare genes with large effects. These studies only merely show associations between genes and traits, not causation. Another issue is population stratification—which is “differences in allele frequencies between cases and controls due to systematic differences in ancestry” (Freedman et al, 2004). GWAS, then, are compromised by this stratification, and attempts to correct for it have been found wanting (Richardson, 2017; Richardson and Jones, 2019; Richardson, 2022). There is also the fact that larger sample sizes won’t help the endeavor of proving that genes contribute to psychological traits—since large databases contain arbitrary correlations, then by increasing the sample size this then highly increases the chance for spurious correlations (Claude and Longo, 2017). At the end of the day, the associations found are weak and could possibly even be meaningless (Noble, 2018). There is also the fact that PGS ignore development and epigenetics (Moore, 2023). Basically, genes don’t work how hereditarians need them to.

The fact of the matter is, these research methods continue to push the false dichotomy of nature vs nurture (the first instance of which appeared in a 13th century French novel on gender). There is also the fact that the “laws of behavioral genetics” rest on twin, family and adoption studies. So if the assumptions of these studies are false, then there is no reason why we should accept the conclusions from them. There are no “laws” in biology, especially not the “laws of behavioral genetics.”

Racial hereditarianism

Racial hereditarianism, on the other hand, is the belief that there are inherent, genetic differences in cognitive ability and other psychological traits between racial and ethnic groups. One—most often unstated—claim is that one group of people are inferior to another (as can be evidenced by the labels of the categories used by Terman), and it has been used to justify discriminatory policies and forced sterilization of people found to have lower IQs. Genetic inheritance explains the how and why of some races having higher IQs than others.

The most famous racial hereditarians are Lynn, Rushton, and Jensen. Over the last 50+ years, these authors have dedicated their lives to proving that certain racial groups have higher IQs than others for genetic reasons. These differences aren’t due just to environment or culture, they say, there is a significant genetic component to the differences in scores between racial and ethnic groups. Since IQ is related to success in life—that is, since IQ is needed for success—then what explains average life outcomes between racial and ethnic groups are their IQs and the ultimate cause is their genes which ultimately cause their IQ scores. Due to the strength of genetic factors on IQ, they say (like Jensen), social programs are doomed to fail.

The argument against psychological hereditarianism and racial hereditarianism

The argument against these is simple—the mental is irreducible to the physical and so, while there are of course correlations between “traits” like IQ and genes, that doesn’t mean they’re causal and due to the irreducibility of the mental to the physical, we can’t find what they need us to find in order to prove their theses.

P1: If racial hereditarianism is true, then cognitive differences between racial groups are primarily due to genetic factors.
P2: There is no empirical (or logical) evidence that supports the claim that cognitive differences between racial groups are primarily due to genetic factors.
C: Thus, racial hereditarianism is false.

P1: If psychological hereditarianism is true, then individual differences in psychological traits are due primarily to genetic factors.
P2: There is no empirical (or logical) evidence that supports the claim that individual differences in psychological traits are primarily due to genetic factors.
C: Thus, psychological hereditarianism is false.

The irreducible complexity of mental states/psychological traits means that it’s impossible for them to be caused or influenced by genetics meaning that both psychological and racial hereditarianism are false. Both psychological and racial hereditarianism, as their unstated assumptions, rely on a type of physicalism to where mental states can be reduced to genes or the brain/brain states. Both kinds are a physicalist theory of mind, and since physicalism is false so are psychological and racial hereditarianism. This is yet more evidence that hereditarianism is false and so it strengthens the argument for banning IQ tests.

Conclusion

Both forms of hereditarianism I’ve discussed here are false, and ultimately they are false since the mental is reducible to the physical. Both of them, however, are inherently reductionist and attempt to reduce people to their genes or their brains. They have, in the past, led to the sterilization of certain people deemed “unfit.” Of course, the hereditarian hypothesis isn’t necessarily racist, though it can be used for racist aims. It can also be used for classist aims. It can be launched at whatever a society deems “unfit”, and then they can try to correlate biological factors with what they deem “unfit.” The very notion that certain races are superior or inferior on intelligence is a form of racism. Such ideas have been used in the recent past in order to justify discriminatory policies against people. So while the psychological hereditarian hypothesis may not be racist (it could be classist, though), how it has been articulated and then even put into practice is inherently racist. In any case, here’s the argument that the hereditarian hypothesis is a racist hypothesis.

P1: If the hereditarian hypothesis is true, then differences in IQ and other traits among racial and ethnic groups are primarily due to genetic factors rather than environmental or social factors.
P2: Differences in IQ and other traits among racial and ethnic groups are not primarily due to genetic factors, but rather environmental or social factors.
C1: Therefore, the hereditarian hypothesis is not true.
P3: If the hereditarian hypothesis is not true, then it cannot be used to make claims about inferiority or superiority.
P4: The hereditarian hypothesis has, historically been used to make claims about the innate superiority or inferiority of certain racial groups, thereby justifying discriniminatory policies and harmful stereotypes.
C2: Therefore, the hereditarian hypothesis is a racist hypothesis.

I’ve shown how P1 and P2 are true exhaustively, so C1 follows from those 2 premises. P3 follows from the conclusion in C1, and P4 is a historical fact. So C2 follows. So by referring to the hereditarian hypothesis as a racist hypothesis, I mean that the hypothesis has been entangled with racist and discriniminatory policies since it’s inception.

So I have articulated a distinction between psychological and racial hereditarianism, where psychological hereditarianism is about the genetic transmission of psychological traits and where racial hereditarianism is the belief that there are inherent racial differences in psychological traits due to genetic differences between groups. While there are of course genetic differences between groups and individuals, it doesn’t follow that said genetic differences cause differences in psychological traits, which is the main claim of hereditarianism. The issue of the reducibility of the mental isn’t an empirical matter, it’s a conceptual one. So the hereditarian hypothesis, therefore, is refuted on conceptual, a priori grounds.