3100 words

“Biological systems are complex, non-linear, and non-additive. Heritability estimates are attempts to impose a simplistic and reified dichotomy (nature/nurture) on non-dichotomous processes.” (Rose, 2006)

“Heritability estimates do not help identify particular genes or ascertain their functions in development or physiology, and thus, by this way of thinking, they yield no causal information.” (Panofsky, 2016: 167)

“What is being reported as ‘genetic’, with high heritability, can be explained by difference-making interactions between real people. In other words, parents and children are sensitive, reactive, living beings, not hollow mechanical or statistical units.” (Richardson, 2022: 52)

Introduction

In the world of behavioral genetics, it is claimed that studies of twins, adoptees and families can point us to the interplay between genetic and environmental influences on complex behavioral traits. To study this, they use a concept called “heritability”—taken from animal breeding—which estimates the the degree of variation in a phenotypic trait that is due to genetic variation amongst individuals in the studied population. But upon the advent of molecular genetic analysis after the human genome project, something happened that troubled behavioral genetic researchers: The heritability estimates gleaned from twin, family and adoption studies did not match the estimates gleaned from the molecular genetic studies. This then creates a conundrum—why do the estimates from one way of gleaning heritability don’t match to other ways? I think it’s because biological models represent a simplistic (and false) model of biological causation (Burt and Simon, 2015; Lala, 2023). This is what is termed “missing heritability.” This raises questions that aren’t dissimilar to when a child dissappears.

Imagine a missing child. Imagine the fervor a family and authorities go through in order to find the child and bring them home. The initial fervor, the relentless pursuit, and the agonizing uncertainty constitute a parallel narrative in behavioral genetics, where behavioral geneticists—like the family of a missing child and the authorities—find themselves grappling with unforseen troubles. In this discussion, I will argue that the additivity assumption is false, that this kind of thinking is a holdover from the neo-Darwinian Modern Synthesis, that hereditarians have been told for decades that heritability just isn’t useful for what they want to do, and finally “missing heritability” and missing children are in some ways analogous, but that there is a key difference: The missing children actually existed, while the “missing heritability” never existed at all.

The additivity assumption

Behavioral geneticists pay lip service to “interactions”, but then conceptualize these interactions as due to additive heritability (Richardson, 2017a: 48-49). But the fact of the matter is, genetic interactions create phantom heritability (Zuk et al, 2012). When it comes to the additive claim of heritability, that claim is straight up false.

The additive claim is one of the most important things for the utility of the concept of heritability for the behavioral geneticist. The claim that heritability estimates for a trait are additive means that the contribution of each gene variant is independent and they all sum up to explain the overall heritability (Richardson 2017a: 44 states that “all genes associated with a trait (including intelligence) are like positive or negative charges“). But in reality, gene variants aren’t independent effects, they interact with other genes, the environment and other developmental resources. In fact, violations of the additivity assumption are large (Daw, Guo, and Harris, 2015).

Gene-gene, gene-environment, and environmental factors can lead to overestimates of heritability, and they are non-additive. So after the 2000s with the completion of the human genome project, these researchers realized that the genetic variants that heritability they identified using molecular genetics did not jive with the heritability they computed from twin studies from the 1920s until the late 1990s and then even into the 2020s. So the expected additive contribution of heritability fell short in actually explaining the heritability gleaned from twin studies using molecular genetic data.

Thinking of heritability as a complex jigsaw puzzle may better help to explain the issue. The traditional view of heritability assumes that each genetic piece fits neatly into the puzzle to then complete the overall genetic picture. But in reality, these pieces may not be additive. They can interact in unexpected ways which then creates gaps in our understanding, like a missing puzzle piece. So the non-additive effects of gene variants which includes interactions and their complexities, can be likened to missing pieces in the heritability puzzle. The unaccounted-for genetic interactions and nuances then contribute to what is called “missing heritability.” So just as one may search and search for missing puzzle pieces, so to do behavioral geneticists search and search for the “missing heritability”.

So heritability assumes no gene-gene and gene-environment interaction, no gene-environment correlation, among other false or questionable assumptions. But the main issue, I think, is that of the additivity assumption—it’s outright false and since it’s outright false, then it cannot accurately represent the intricate ways in which genes and other developmental resources interact to form the phenotype.

If heritability estimates assume that genetic influences on a trait are additive and independent, then heritability estimates oversimplify genetic complexity. If heritability estimates oversimplify genetic complexity, then heritability estimates do not adequately account for gene-environment interactions. If heritability does not account for gene-environment interactions, then heritability fails to capture the complexity of trait inheritance. Thus, if heritability assumes that genetic influences on a trait are additive and independent, then heritability fails to capture the complexity of trait inheritance due to its oversimplified treatment of genetic complexity and omission of gene-environment interactions.

One more issue, is that of the “heritability fallacy” (Moore and Shenk, 2016). One commits a heritability fallacy when they assume that heritability is an index of genetic influence on traits and that heritability can tell us anything about the relative contribution of trait inheritance and ontogeny. Moore and Shenk (2016) then make a valid conclusion based on the false belief that heritability us anything about the “genetic strength” on a trait:

In light of this, numerous theorists have concluded that ‘the term “heritability,” which carries a strong conviction or connotation of something “[in]heritable” in the everyday sense, is no longer suitable for use in human genetics, and its use should be discontinued.’31 Reviewing the evidence, we come to the same conclusion. Continued use of the term with respect to human traits spreads the demonstrably false notion that genes have some direct and isolated influence on traits. Instead, scientists need to help the public understand that all complex traits are a consequence of developmental processes.

“Missing heritability”, missing children

Twin studies traditionally find heritability to be estimated between 50 and 80 percent for numerous traits (eg Polderman et al, 2015; see Joseph’s critique). But as alluded to earlier, molecular studies have found heritabilities of 10 percent or lower (eg, Sniekers et al, 2017; Savage et al, 2018; Zabaneh et al, 2018). This discrepancy between different heritability estimates using different tools is what is termed “missing heritability” (Mathhews and Turkheimer, 2022). But the issue is, increasing the sample sizes will merely increase the chance of spurious correlations (Calude and Longo, 2018), which is all these studies show (Richardson, 2017b; Richardson and Jones, 2019).

This tells me one important thing—behavioral geneticists have so much faith in the heritability estimates gleaned from twin studies that they assume that the heritability is “missing” in the newer molecular genetic studies. But if something is “missing”, then that implies that it can be found. They have so much faith that eventually, as samples get higher and higher in GWAS and similar studies, that we will find the heritability that is missing and eventually, be able to identify genetic variants responsible for traits of interest such as IQ. However I think this is confused and a simple analogy will show why.

When a child goes missing, it is implied that they will be found by authorities, whether dead or alive. Now I can liken this to heritability. The term “missing heritability” comes from the disconnect between heritability estimates gleaned from twin studies and heritability estimates gleaned from molecular genetic studies like GWAS. So the implication here is, since twin studies show X percent heritability (high heritability), and molecular genetic studies show Y percent heritability (low heritability) – which is a huge difference between estimates between different tools – then the implication is that there is “missing heritability” that must be explained by rare variants or other factors.

So just like parents and authorities try so hard to find their missing children, so to do behavioral geneticists try so hard to find their “missing heritability.” As families endure anguish as they try to find their children, this is then mirrored in the efforts of behavioral geneticists to try and close the gap between two different kinds of tools that glean heritability.

But there is an important issue at play here—namely the fact that missing children actually exist, but “missing heritability” doesn’t, and that’s why we haven’t found it. Although some parents, sadly, may never find their missing children, the analogy here is that behavioral geneticists will never find their own “children” (their missing heritability) because it simply does not exist.

Spurious correlations

Even increasing the sample sizes won’t do anything, since the larger the sample size, the bigger chance for spurious correlations, and that’s all GWAS studies for IQ are (Richardson and Jones, 2019), while correlations with GWAS are inevitable and meaningless (Richardson, 2017b). Denis Noble (2018) puts this well:

As with the results of GWAS (genome-wide association studies) generally, the associations at the genome sequence level are remarkably weak and, with the exception of certain rare genetic diseases, may even be meaningless (13, 21). The reason is that if you gather a sufficiently large data set, it is a mathematical necessity that you will find correlations, even if the data set was generated randomly so that the correlations must be spurious. The bigger the data set, the more spurious correlations will be found (3). The current rush to gather sequence data from ever larger cohorts therefore runs the risk that it may simply prove a mathematical necessity rather than finding causal correlations. It cannot be emphasized enough that finding correlations does not prove causality. Investigating causation is the role of physiology.

Nor does finding higher overall correlations by summing correlations with larger numbers of genes showing individually tiny correlations solve the problem, even when the correlations are not spurious, since we have no way to find the drugs that can target so many gene products with the correct profile of action.

The Darwinian model

But the claim that there is a line that goes from G (genes) to P (phenotype) is just a mere holdover from the neo-Darwinian modern synthesis. The fact of the matter is, “HBD” and hereditarianism are based on reductionistic models of genes and how they work. But the reality is, genes don’t work how they think they do, reality is much more complex than they assume. Feldman and Ramachandran (2018) ask “Missing compared to what?”, effectively challenging the “missing heritability” claim. As Feldman and Ramachandran (2018) ask, would Herrnstein and Murray have written The Bell Curve if they believed that the heritability of IQ were 0.30? I don’t think they would have. In any case, such a belief in the heritability of IQ being between 0.4 and 0.8 shows the genetic determinist assumptions which are inherent in this type of “HBD” genetic determinist thinking.

Amusingly, as Ned Block (1995) noted, Murray said in an interview that “60 percent of the intelligence comes from heredity” and that that heritability is “not 60 percent of the variation. It is 60 percent of the IQ in any given person.” Such a major blunder from one of the “intellectual spearheads” of the “HBD race realist” movement…

Behavioral geneticists claim that the heritability is missing only because sample sizes are low, and as sample sizes increase, the missing heritability based on associated genes will be found. But this doesn’t follow at all since increasing sample sizes will just increase spurious hits of genes correlated with the trait in question but it says absolutely nothing about causation. Nevertheless, only a developmental perspective can provide us mechanistic knowledge and so-called heritability of a phenotype cannot give us such information because heritability isn’t a mechanistic variable and doesn’t show causation.

Importantly, a developmental perspective provides mechanistic knowledge that can yield practical treatments for pathologies. In contrast, information about the “heritability” of a phenotype—the kind of information generated by twin studies—can never be as useful as information about the development of a phenotype, because only developmental information produces the kind of thorough understanding of a trait’s emergence that can allow for successful interventions. (Moore 2015: 286)

The Darwinian model and it’s assumptions are inherent in thinking about heritability and genetic causation as a whole and are antithetical to developmental, EES-type thinking. Since hereditarianism and HBD-type thinking are neo-Darwinist, it then follows that such thinking is inherent in their beliefs, assumptions, and arguments.

Conclusion

Assumptions of heritability simply do not hold. Heritability, quite simply, isn’t a characteristic of traits but it is a characteristic of “relationships in a population observed in a particular setting” (Oyama, 1985/2000). Heritability estimates tell us absolutely nothing about development, nor the causes of development. Heritability is a mere breeding statistic and tells us nothing at all about the causes of development or whether or not genes are “causal” for a trait in question (Robette, Genin, and Clerget-Darpoux, 2022). It is key to understand that heritability along with the so-called “missing heritability” are based on reductive models of genetics that just do not hold, especially with newer knowledge that we have from systems biology (eg, Noble, 2012).

The assumption that heritability estimates tell us anything useful about genetics, traits, and causes along with a reductive belief in genetic causation for the ontogeny of traits has wasted millions of dollars. Now we need to grapple with the fact that heritability just doesn’t tell us anything about genetic causes of traits, but that genes are necessary, not sufficient, causes for traits because no genes (along with other developmental resources) means no organism. Also coming from twin, family and adoption studies are Turkheimer’s (2000) so-called “laws of behavioral genetics.” Further, the falsity of the EEA (equal environments assumption) is paramount here, and since the EEA is false, genetic conclusions from such studies are invalid (Joseph et al, 2015). There is also the fact that heritability is based on a false biological model. The issue is that heritability rests on a “conceptual model is unsound and the goal of heritability studies is biologically nonsensical given what we now know about the way genes work” (Burt and Simons, 2015: 107). What Richardson (2022) terms “the agricultural model of heritability” is known as false. In fact, the heritability of “IQ” is higher than any heritability found in the animal kingdom (Schonemann, 1997). Why this doesn’t give any researcher pause is beyond me.

Nonetheless, the Darwinian assumptions that are inherent in behavioral genetic, HBD “race realist” thinking are false. And the fact of the matter is, increasing the sample size of molecular genetic studies will only increase the chances of spurious correlations and picking up population stratification. So, it seems that using heritability to show genetic and environmental causes is a bust and has been a bust ever since Jensen revived the race and IQ debate in 1969, along with the subsequent responses that Jensen received against his argument which then led to the 1970s as being a decade in which numerous arguments were made against the concept of heritability (eg, Layzer, 1974).

It has also been pointed out to racial hereditarians for literally decades that heritability is is a flawed metric (Layzer, 1974; Taylor, 1980; Bailey, 1997; Schonemann, 1997; Guo, 2000; Moore, 2002; Rose, 2006; Schneider, 2007; Charney, 2012, 2013; Burt and Simons, 2015; Panofsky, 2014; Joseph et al, 2015; Moore and Shenk, 2016; Panofsky, 2016; Richardson, 2017; Lerner, 2018). These issues—among many more—lead Lerner to conclude:

However, the theory and research discussed across this chapter and previous ones afford the conclusion that no psychological attribute is pre-organized in the genes and unavailable to environmental influence. That is, any alleged genetic difference (or “inferiority”) of African Americans based on the high heritability of intelligence would seem to be an attribution built on a misunderstanding of concepts basic to an appropriate conceptualization of the nature–nurture controversy. An appreciation of the coaction of genes and context—of genes↔context relations—within the relational developmental system, and of the meaning, implications, and limitations of the heritability concept, should lead to the conclusion that the genetic-differences hypothesis of racial differences in IQ makes no scientific sense. (Lerner, 2018: 636)

That heritability doesn’t address mechanisms and ignores genetic factors, along with being inherently reductionist means that there is little to no utility of heritability for humans. And the complex, non-additive, non-linear aspects of biological systems are attempts at reducing biological systems to their component parts, (Rose, 2006), making heritability, again, inherently reductionist. We have to attempt to analyzed causes, not variances (Lewontin, 1974), which heritability cannot do. So it’s very obvious that the hereditarian programme which was revived by Jensen (1969)—and based on twin studies which were first undertaken in the 1920s—is based on a seriously flawed model of genes and how they work. But, of course, hereditarians have an ideological agenda to uphold, so that’s why they continue to pursue “heritability” in order to “prove” that “in part”, racial differences in many socio-behavioral traits—IQ included—are due to genes. But this type of argumentation quite clearly fails.

The fact of the matter is, “there are very good reasons to believe gene variations are at best irrelevant to common disorders and at worst a distraction from the social and political roots of major public health problems generally and of their unequal distribution in particular” (Chaufan and Joseph 2013: 284). (Also see Joseph’s, 2015 The Trouble with Twin Studies for more argumentation against the use of heritability and it’s inflation due to false assumptions along with arguments against “missing heritability.”) In fact, claims of “missing heritability” rest on “genetic determinist beliefs, a reliance on twin research, the use of heritability estimates, and the failure to seriously consider the possibility that presumed genes do not exist” (Joseph, 2012). Although it has been claimed that so-called rare variants explain the “missing heritability” (Genin, 2020), this is nothing but cope. So the heritability was never missing, it never existed at all.