But there are even more problems: heritability refers only to the % of variation of genetic origin in a given population and in a given environment, so changes in the environment can always affect how heritable something is.\cite{Rose_2006} Not only that, but heritability also says nothing about the relative influence of genes or environment on a trait, and since genes definitely have to do with almost all human traits, knowing the percent "heritability" of any such trait is almost always useless.\cite{Moore_2016} Clearly, the common view that high heritability is indicative of current low environmental influence for any trait, or a lack of susceptibility of that trait to environmental changes, is entirely wrong.\cite{Tucker_Drob_2013}\cite{Hopper_2017}
Validated?
One of the key arguments used by BGists to defend the CTD doesn't really fit neatly into any of the categories above. Instead, it is used as though it by itself could answer all the criticisms above, and any other criticisms that could be made of the methodology. This is the argument that the results of CTD studies can be "validated" by producing similar estimates of heritability using different methodologies.
Thus, if this kind of replication of results is found when using non-CTD methods, it is cited by BGists as slam-dunk evidence that the CTD is valid for estimating heritability. One of the main reasons for this argument's strength (apparent or real) is that CTD studies are based on different assumptions than other genetic study designs (specifically, reared-apart twins, family, and adoption studies). One of the main reasons for this argument's strength (apparent or real) is that CTD studies are based on different assumptions than other genetic study designs (specifically, reared-apart twins, family, and adoption studies).
So here are some examples of BGists making this argument (all emphases are mine):
- "Heritability estimates for CB (criminal behavior) from full- and half-siblings closely approximated those found from twins in the same population, validating the twin method."\cite{Kendler2015}
- "For the three externalizing syndromes examined, concerns that heritability estimates from twin studies are upwardly biased...were not supported...The heritability estimates for CB, AUD (alcohol use disorder) and DA (drug abuse) that we obtained from our sibling trios were very similar to those obtained from MZ and DZ twins from the same population using the same diagnostic methods."\cite{Kendler_2016}
- "Moving beyond the twin‐only design leads to the conclusion that for most political and social attitudes, genetic influences account for an even greater proportion of individual differences than reported by studies using more limited data and more elementary estimation techniques."\cite{Hatemi_2010}
- " The aim of the current study is to characterize more reliably than previously possible ECG [electrocardiogram] trait h2 using GREML estimation, and to compare these outcomes to those of the classical twin model...We found no evidence that the classical twin model leads to inflated h2 estimates."\cite{Nolte2017}
- Not too long ago, I sent an email to prominent twin researcher Dorret Boomsma, asking her about how she would respond to classical twin studies' critics. In her reply (which I received July 17, 2018), Boomsma said that she would respond to them by "...pointing to the empirical evidence from extended twin-family designs and molecular studies, which all confirm findings from the classical twin design, as well as findings from twins reared apart studies."
- In a 2016 article in the Guardian written as a response to Oliver James, Marcus Munafo argues, "Twin, family and adoption studies...have been criticized...However, two lines of evidence give us confidence in the overall conclusion. First, many of the assumptions have been directly tested and shown to hold, at least sufficiently to mean that the method is valid. Second, and more importantly, each method relies on a different set of assumptions, and yet they all give very consistent results. It’s highly unlikely that invalid assumptions across all of these methods would distort the results in exactly the same way." (My emphasis.)\cite{are}
- "Although the twin and adoption designs have separately been criticized, these two designs generally converge on the same conclusion, despite making very different assumptions, which adds strength to these conclusions."\cite{Plomin_2016}
So this argument is supposed to show that twin studies are a valid research design for estimating heritabilities because other methods (even if they have also been criticized for having flaws) yield similar results.
As you can imagine, critics of BG have responded to this response already. For instance, Joseph et al. (2015) argued, "there are major problems with previous criminal and ASB [antisocial behavior] adoption studies, many of which were discussed by Burt and Simons, and reared-apart twin studies are greatly flawed on several critical dimensions."\cite{jay2015}
The tactic of persecution
BGists love to construct a persecution complex that they supposedly are hindered by in their research, bravely challenging the orthodox view that all social behaviors are entirely determined by the environment. For instance, Hatemi et al. (2014) write that "The notion of a genetically informed model of attitudes and ideology, understood as a psychological disposition that guides behavior, independent of, and interacting with, social forces presented a fundamental challenge to the dominant rational choice and behaviorist social science paradigms." Thus they portray themselves as bravely going wherever the evidence leads, though they give their ideological genetic-determinist agenda away later in the same paper, when they cite criticism that BG studies of political behavior as "limiting the integration of biological factors into mainstream conceptualizations of political ideology."\cite{Hatemi_2014} Certainly, such a statement seems to indicate that whoever would write or say it would view biological factors as inherently important in political ideology, as an a priori belief, no matter what the evidence really says, no?
I am not the first to note this weird ad hominem tactic of BGists responding to scientific criticisms by accusing their critics of being political ideologues set to deny the potential for biological influences on human behavior. Panofsky even came up with a name for it: the "hitting-them-over-the-head style" (Misbehaving Science, page 142). Like global warming deniers, they will paint themselves as being persecuted for their "heretical" or "politically incorrect" beliefs that challenge the "dogma" of the scientific establishment. But while global warming deniers claim to be questioning the dogma of mainstream global warming science, BGists portray themselves as bravely fighting against the dogmatic beliefs of environmental determinism and the assumption of a total lack of biological or genetic influence on human behavior.
I will close this section by citing more examples of the "hitting-them-over-the head" approach used by BGists dismissing critics as ideologically motivated to deny the role of genes in human behavior completely. Enjoy! (Note: all emphases below are mine.)
- "A disconnect has developed between criticisms that focus on improving existing models and those that seek to abolish or eliminate the entire research agenda, oftentimes for ideological reasons, such as wholesale objections to biological work because of fear of past abuse, or threats to current dominant models. As a result of such largely unspoken existential divides, it has proven difficult for life and social scientists to enter an honest discussion about the limitations inherent in genetic work and still employ the methods in a progressive and useful manner."\cite{Hatemi_2012}
- " Since its inception, [behavior genetics] has been a lightning rod of criticism, especially by scholars who are inalterably opposed to linking biology with behavior."\cite{BARNES_2014}
- " Beginning in the 1970s, politically motivated critics of behavioral genetics launched an all‐out crusade against such methods, the findings emanating from them, and even on the researchers themselves (Segerstråle, 2000). These critics called for an end to the idea that biology had anything to do with behavior, noting that sociobiology was a “dangerous idea.” "\cite{BARNES_2014}