2400 words

In the year 2000, psychologist Erik Turkheimer proposed three “laws of behavioral genetics” (LoBG hereafter):

● First Law. All human behavioral traits are heritable.
● Second Law. The effect of being raised in the same family is smaller than the effect of genes.
● Third Law. A substantial portion of the variation in complex human behavioral traits is not accounted for by the effects of genes or families. (Turkheimer, 2000: 160)

In March of 2021, I asked Turkheimer how he defined “law.” He responded: “With tongue in cheek. In fact, it’s a null hypothesis: an expected result when nothing in particular is going on.“

In 2015, Chabris et al (2015) proposed a 4th “law”, that a typical behavioral trait is associated with many variants which each explain a small amount of behavioral variability. They state that the “4th law” explains the failure of candidate gene studies and also the need for higher sample sizes in GWA studies. (It seems they are not aware that larger sample sizes increase the probability of spurious correlations—which is all GWA studies are; Claude and Longo, 2016; Richardson, 2017; Richardson and Jones, 2019) Nice ad hoc hypothesis to save their thinking.

One huge proponent of the LoBG is JayMan, who has been on a crusade for years pushing this nonsense. He added a “5th law” proposed by Emil Kirkegaard, which states that “All phenotypic relationships are to some degree genetically mediated or confounded.”

But what is a “law” and are these “laws of behavioral genetics” laws in the actual sense? First I will describe what a “law” is and if there even are biological laws. Then I will address each “law” in turn. I will then conclude that the LoBG aren’t real “laws”, they are derived from faulty thinking about the relationship between genes, traits, environment and the system and how the “laws” were derived rest on false assumptions.

What is a law? Are there biological laws?

Laws are “true generalizations that are “purely quantitative” … They have counterfactual force” (Sober, 1993: 458). Philosopher of mind Donald Davidson argued that laws are strict and exceptionless (Davidson, 1970; David-Hillel, 2003). That is, there must be no exceptions for that law. Sober (1993) discusses Rosenberg’s and Beatty’s arguments against laws of biology—where Rosenberg states that the only law in biology is “natural selection.” (See Fodor, 2008 and Fodor and Piattelli-Palmarini, 2009, 2010 for the argument against that claim and for arguments against the existence of laws of selection that can distinguish between causes and correlates of causes.) It has even been remarked that there are “so few” laws in biology (Dhar and Giuliani, 2010; also see Ruse, 1970).

Biology isn’t reducible to chemistry or physics (Marshal, 2021), since there are certain things about biology that neither chemistry or physics have. If there are laws of biology, then they will be found at the level of the organism or its ecology (Rull, 2022). In fact, it seems that although three laws of biology have been proposed (Trevors and Sailer Jr., 2008), they appear to be mere regularities, including McShea and Brandon’s (2010) first law of biology; all “laws of biology” seem to be mere laws of physics (Wayne, 2020). The “special sciences”, it seems, “are not fit for laws” (Kim, 2010). There seem to be, though, no uncontroversial laws or regularities in biology (Hamilton, 2007).

Now that I have described what laws are and have argued that there probably aren’t any biological laws, what does that mean for the LoBG? I will take each “law” in turn.

“Laws” of behavioral genetics

(1) All human behavioral traits are heritable.

JayMan gives derivations for the “laws”, and (1) and (2) have their bases in twin studies. We know that the equal environments assumption is false (Charney, 2012; Joseph, 2014; Joseph et al, 2015), and so if the EEA is false then we must reject genetic claims from twin study proponents. Nevertheless, the claim that these “laws” have any meaning gets pushed around a lot.

When it comes to the first law, the claim is that “ALL human behavioral traits are heritable”—note the emphasis on “ALL.” So this means that if we find only ONE behavioral trait that isn’t heritable, then the first law is false.

Reimann, Schilke, and cook (2017) used a sample of MZ and DZ twins and asked questions related to trust and distrust. They, of course, claim that “MZ and DZ twins share comparable environments in their upbringing“—which is false since MZ twins have more comparable environments. Nevertheless, they conclude that while trust has a heritability or 30%, “ACE analyses revealed that the estimated heritability [for] distrust is 0%.” This,therefore, means, that the “1st law” is false.

This “first law”, the basis of which is twin, family, and adoption studies, is why we have poured countless dollars into this research, and of course people have their careers (in what is clear pseudoscience) to worry about, so they won’t stop these clearly futile attempts in their search for “genes for” behavior.

(2) The effect of being raised in the same family is smaller than genes.

This claim is clearly nonsense, and one reason why is that the first “law” is false. In any case, there is one huge effect on, children’s outcomes due to birth order and how, then, parental attitudes–particularly mothers—affect child outcomes (Lehmann, Nuevo-Chiquero, and Vidal-Fernandez, 2018).

Why would birth order have an effect? Quite simply, the first-born child will get more care and attention than children who are born after, and so variations in parental behavior due to birth order can explain differences in education and life outcomes. They conclude that “broad shifts in parental behavior appear to set later-born children on a lower path for cognitive development and academic achievement, with lasting impact on adult outcomes.” Thus, Murray’s (2002) claim that birth order doesn’t matter and JayMan’s claim that “that the family/rearing environment has no effect on eventual outcomes” is clearly false. Thus, along with this and the falsity of the “1st law”, the “2nd law” is false, too.

(3) A substantial portion of the variation in complex human behavioral traits is not accounted for by the effects of genes or families.

This “law” covers the rest of the variance not covered in the first two “laws.” It was coined due to the fact that the first two “laws” had variance left that wasn’t “explained” by them. So this is basically unique experience. This is what behavioral genetics call “non-shared environment.” Of course, unique experiences (that is, subjective experiences) would definitely “shape who we are”, and part of our unique experiences are cultural. We know that cultural differences can have an impact on psychological traits (Prinz, 2014: 67). So the overall culture would explain why these differences aren’t “accounted for” in the first two “laws.”

Yet, we didn’t need the LoBG for us to know that individual differences are difference-makers for differences in behavior and psychology. So this means that what we choose to do can affect our propensities and then, of course, our behavior. Non-shared environmental effects are specific to the individual, and can include differing life events. That is, they are random. Non-shared environment, then, is parts of the environment that aren’t shared. Going back to Lehmann, Nuevo-Chiquero, and Vidal-Fernandez (2018) above, although children to grow up in the same family under the same household, they are different ages and so they also experience different life events. They also experience the same things differently, due to the subjectivity of experience.

In any case, the dichotomy between shared and non-shared environment is a dichotomy that upholds the behavioral geneticists main tool—the heritability estimate—from which these “laws” derive (from studies of twins, adoptees, and families). So, due to how the law was formulated (since there were still portions “unaccounted for” by the first two “laws”), it doesn’t really matter and since it rests on the first two false “laws”, therefore the third “law” is also false.

(4) Human behavioral traits are associated with many genes of small effect which contribute to a small amount of behavioral variability.

This “law” was formulated by Chabris et al (2015) due to the failure of molecular genetic studies which hoped to find genes with large effects to explain behavior. This “law” also “explains why the results of “candidate-gene” studies, which focus on a handful of genetic variants, usually fail to replicate in independent samples.” What this means to me is simple—it’s an ad-hoc account, meaning it was formulated to save the gene-searching by behavioral geneticists since the candidate gene era was a clear failure, as Jay Joseph noted in his discussion of the” 4th law.”

So here is the time line:

(1) Twin studies show above-0 heritabilities for behavioral traits.

(2) Since twin studies show high heritabilities for behavioral traits, then there must be genes that will be found upon analyzing the genome using more sophisticated methods.

(3) Once we started to peer into the genome after the completion of the human genome project, we then came to find candidate genes associated with behavior. Candidate gene studies “look at the genetic variation associated with disease within a limited number of pre-specified genes“, they refer to genes “believed to be” associated with a trait in question. Kwon and Goat (2000) wrote that “The candidate gene approach is useful for quickly determining the association of a genetic variant with a disorder and for identifying genes of modest effect.” But Sullivan (2020) noted that “Historical candidate gene studies didn’t work, and can’t work.” Charney (2022) noted that the candidate gene era was a “failure” and is now a “cautionary tale.”

Quite clearly, they were wrong then, and the failure of the candidate gene era led to the ad-hoc “4th law.” This has then followed us to the GWAS and PGS era, where it is claimed that we aren’t finding all of the heritability that twin studies say we should find with GWAS, since the traits under review are due to many genes of small effect. It’s literally just a shell game—when one claim is shown to be false, just make a reason why what you thought would be found wasn’t found, and then you can continue to search for genes “for” behavior. But genetic interactions create a “phantom heritability” (Zuk et al, 2011), while behavioral geneticists assume that the interactions are additive. They simply outright ignore interactions, although they pay it lip service.

So why, then, should we believe behavioral geneticists today in 2023 that we need larger and larger samples to find these mythical genes “for” behavior using GWAS? We shouldn’t. They will abandon GWAS and PGS in a few years when the new kid on the block shows up that they can they champion and claim that the mythical genes “for” behavior will finally be found.

(5) All phenotypic relationships are to some degree genetically mediated or confounded.

This claim is something that comes up a lot—the claim of genetic confounding (and mediation). A confound is a third variable that influences both the dependent and independent variable. The concept of genetic confounding was introduced during the era where it was debated whether or not smoking caused lung cancer (Pingault et al, 2021). (Do note that Ronald Fisher (1957), who was a part of this debate, claimed that smoking and lung cancer were both “influenced by a common cause, in this case individual genotype.“

However, in order for the genetic confounding claim to work, they need to articulate a mechanism that explains the so-called genetic confounding. They need to articulate a genetic mechanism which causally explains X and Y, explains X independent of Y and explains Y independent of X. So for the cop-out genetic confounding claim to hold any water: G confounds X and Y iff there is a genetic mechanism which causally explains X and Y, causally explains X independent of Y and Y independent of X.

Conclusion

The “laws of behavioral genetics” uphold the false dichotomy of genes and environment, nature and nurture. Though, developmental systems theorists have rightly argued that it is a false dichotomy (Homans, 1979; Moore, 2002; Oyama, 2002; Moczek, 2012) and that it is just not biologically plausible (Lewkowicz, 2012). In fact, the h2 statistics assumes that G and E are independent, non-interacting factors, so if the claim is false then—for one of many reasons—we shouldn’t accept their conclusions. The fact that G and E interact means that, of course, we should reject h2 estimates, and along with it, the entire field of behavioral genetics.

Since the EEA is false, h2 equals c2. Furthermore, h2 equals 0. So Polderman’s (2015) meta analysis doesn’t show that for all traits in the analysis that h2 equals 49%. (See Jay Joseph’s critique.) Turkheimer (2000: 160) claimed that the nature-nurture debate is over, since everything is heritable. However, the debate is over because developmental systems approach has upended the false dichotomy of nature vs nurture, since all developmental resources interact and are therefore irreducible to development.

However, for the field to continue to exist, they need to promulgate the false dichotomy, since their heritability estimates depend on it. They also need to hold onto the claim that twin, family and adoption studies can show the “genetic influence” on traits to justify the continued search for genes “for” behavior. Zuk and Spencer (2020) called the nature-nurture “debate” “a zombie idea, one that, no matter how many times we think we have disposed of it, springs back to life.” This is just like Oyama (2000) who compared arguing against gene determinism like battling the undead (Griffiths, 2006).

Jay Joseph proposed a 5th “law” in 2015 where he stated:

Behavior genetic Laws 1-4 should be ignored because they are based on many false assumptions, concepts, and models, on negative gene finding attempts, and on decades of unsubstantiated gene discovery claims.

The “laws” should quite obviously be ignored. Since the whole field of behavioral genetics is based on them, why not abandon the search for “genes for behavior”? At the end of the day, it seems like there are no “laws” of behavioral genetics, since laws are strict and exceptionless. So why do they keep up with their claims that their “laws” tell us anything about human behavior? Clearly, it’s due to the ideology of those who hold that the all-important gene causes traits and behavior, so they will do whatever it takes to “find” them. But in 2023, we know that this claim is straight up false.