Genetic Denialism: Debunking the Popular Anti-Scientific Ideology
Introduction
Genetic denialism is a popular belief where it is assumed that most or all psychological and some physical traits are not and can not be influenced or determined by genetics. This idea is not supported by empirical evidence nor theoretical understanding of the scientific concepts implicated, and is largely based on misunderstanding & misrepresentation of scientific concepts and evidence and what they mean, and also appears to be largely motivated by political and moralistic reasons. In this post I examine the motivations behind genetic denialism (including an evolutionary hypothesis for genetic denialism), the statistical evidence against genetic denialism, why the idea does not make sense theoretically, and why genetic denialism does not promote social justice.
Genetic Influences of Traits
In this section I will review several traits which are commonly denied to have a genetic component and the evidence of their genetic basis. A decently reliable way to test how much genetics influence a trait is through a twin study: if a trait is determined by genetics, two people with different lives, raised in different environments that are genetically identical should have about the same degree of that trait. For example, if one person is tall and the other is short, their twins would also be tall and short respectively, unless height was determined by environment and not genetics. This can be expanded to sets of hundreds or thousands of twins, and can reliably show whether a trait is genetically determined, as well as how much is determined by genetics. The results of twin studies (in twins who were raised by different parents in different environments) for several traits are presented in a table. The genetic correlations of the traits (particularly psychological ones) are likely underestimated because self-report measures of traits are ‘noisy’ meaning that scores are not exact and two people with the exact same degree of a trait may score differently for many reasons - for example, environment might not influence the trait, but may influence the degree to which a person believes that trait applies to them, two people might interpret a questionnaire item as having a different meaning, etc (Cohen 1988).
Theoretical Problems
Among one of the most obvious theoretical problems for genetic denialism is that it suggests genetics work entirely differently in humans than all other species - where non-human animals are widely accepted to have characteristic behaviors that are inherent to their species, it is often denied that human behavior also has a biological basis. Within-species genetic differences are also well known - for example dogs are bred for specific behavioral, emotional, and cognitive traits, and these differences between dog breeds are measurable (e.g., Serpell & Duffy 2014). Genetic disabilities such as down syndrome and prader-willi syndrome are widely known to cause differences in behavior, emotions, and cognition, and the psychological symptoms of genetic syndromes also cluster together to mild degrees in the general population (Salminen et al. 2022), reflecting higher and lower expressions of genes which are fully deleted, duplicated, or drastically altered in these genetic syndromes (Crespi et al. 2018)(Salminen et al. 2020). It is also well known that several drugs can influence behavior, emotions, and cognition by influencing biological processes in the body, for example alcohol temporarily increases sociability, reduces self control, reduces anxiety, and reduces memory, and drugs work by changing the expression of genes and interacting with compounds in the body which are genetically encoded, such as the GABAa receptor protein. Unless one believes in magic, behavior, cognition, and emotions are underpinned by brain activity, which is tied to biological processes, and like other individual differences (such as height, eye color, finger lengths, presence of male/female genitalia, skin color, etc) the complex biological processes underlying them are influenced by genetics. One of many possible examples of how a genetic, biological difference can affect both "physical" and mental aspects of a person is a genetic variation that affects how well the amino acids tyrosine and phenylalanine are absorbed from food - phenylalanine is converted to tyrosine in the body, and tyrosine is converted to dopamine (neurotransmitter that regulates attention, activity, sociability, decision making, cognition, and emotionality), thyroxine (thyroid hormone), and melanin (compound that affects skin pigmentation) (Lerner 2009). If phenylalanine and tyrosine are absorbed to a lesser degree, then the effect would be a reduction in dopamine, thyroxine, and melanin, which then affects behavior, cognition, and emotionality by reduced dopamine, metabolism by reduced thyroxine, and skin pigmentation by reduced melanin. A change in dopamine (or any hormone or neurotransmitter) has a long term effect on how the brain develops (e.g., the formation of memories), no different from how thyroxine has a long term effect on a person's height (Cetinkaya et al. 2003). The brain and body are quite obviously connected, for example it's generally accepted that fear is associated with an increased heart rate and that blood sugar can influence energy and mood - the fact that physically identical twins exist is incompatible with the idea that differences in the brain are uninfluenced by genetically determined biological processes.
Motivations for Genetic Denialism
I suggest that the primary motivation for genetic denialism in a broad sense is for the protection of a moralized view of reality that enables self serving behavior. For example, adherence to social norms is evolutionarily beneficial to survival and reproduction (Crespi & Summers 2014), and the idea that individual differences are explainable by genetics is rejected by individuals who endorse normative and ‘politically correct’ beliefs (Andary-Brophy 2015), and political correctness shares the same psychological, social, and ideological characteristics of religion (Ketelaar 2019) - religiosity largely representing conformity to values, assumptions, and practices associated with a culture (Crespi & Summers 2014). (many individuals also selectively believe in genetic individual differences depending on the topic, for example individuals affiliated with the cultural left may deny the genetic influence on intelligence but not psychiatric disorders like autism or depression, and individuals affiliated with the cultural right may deny the genetic influence on mental health but not intelligence). Many individuals are highly attached to their beliefs of “who” they are, believe they are unique and ‘good’, believe their behaviors are calculated and rational, and may perceive themselves to be defined by certain characteristics which are socially constructed - the fact that individual differences are genetic may contradict these beliefs. These beliefs may be evolutionarily beneficial - for example, the belief in “free will” (as opposed to behavior, thinking, and emotions being caused by biological processes that function differently depending on the individual and its interaction with an individual's circumstances) enables individuals to cause great harm to those who behave in a socially unacceptable manner and a diminished sense of empathy for them, and empathizing with or attempting to provide an explanation for individuals who behave in socially unacceptable ways very often leads to social exclusion.
Genetic denialism often occurs alongside false assumptions of genetic ‘determinism’ having sinister motives behind it, and misinterpretation of its implications. Of course, there are certain groups that have used genetics to justify harmful and discriminatory actions and beliefs, however a large portion of the ‘facts’ these groups present tend to involve oversimplification and misrepresentation of concepts and data. Accurate facts that have been used to support harmful and discriminatory actions and beliefs do not inherently support such actions and beliefs - for example, there is strong evidence that the differences in career choices between men and women are largely due to cognitive and psychological traits that differ on average between men and women due to biological processes (e.g., Berenbaum 2018, Crespi & Go 2015, Billington et al. 2007). This does not imply that men and women should be encouraged to choose careers that are typical for their sex, that it is wrong for individuals to choose careers that are atypical for their sex, that every man or woman is unable to work in professions that are atypical for their sex, etc. In fact, it actually suggests the opposite - that individuals who have career interests atypical of their sex should pursue their interests as it indicates that they are more psychologically “fit” for them (Billington et al. 2007). Differences between men and women also do not imply one sex is “better” than the other - rather, one can only come to this conclusion if they view male-typical traits as better or worse than female-typical traits.
A common line of reasoning used to support genetic denialism is an assumption that psychological traits are too complex to be explained by genetics. However, this relies on oversimplified understandings of what psychological traits are - often in a moralized fashion similar to belief in free will. For example, morality represents several variations in cognition and emotionality that are easily explained biologically. Prosocial, empathetic behavior that is typically considered morally correct is correlated with levels of the neurotransmitter oxytocin, and administration of oxytocin increases prosocial behavior (Crespi 2016). Oxytocin does so through affecting cognitive and emotional processes, such as imagination which is necessary for understanding others mental states (Crespi et al. 2016), and emotionality which allows one to feel the emotions of others (Crespi 2016). Socially deviant behaviors such as engaging in atypical sexual practices or being lazy are related to functioning of the reward system, particularly involving serotonin, where high levels of serotonin are associated with conforming, socially responsible, non-deviant behavior (Fisher et al. 2015)(Allen & DeYoung 2016), and pharmacological agents that increase serotonin are found to reduce deviant behavior (e.g., Kraus et al. 2006). It is thought that serotonin has this effect through reducing emotional reactivity (e.g., by blunting the flight or flight response, reducing the intensity of desire for pleasure, etc) which leads to better self control, cautiousness, etc. It is commonly argued that deviant psychological traits (such as homosexuality) cannot be genetic, because they apparently are not beneficial, however this relies on a massively oversimplified, moralistic understanding of evolution - for example, it might be assumed that "hookup culture" is socially conditioned rather than a product of individual differences in sexuality, because a "broken home" is thought to be harmful to a child's development, however in reality it is an alternative evolutionary strategy that allows for successful reproduction by having many offspring that are "lower quality" rather than few that are raised effortfully, and such a strategy is more effective in dangerous, chaotic environments (e.g., Del Giudice 2018).
The last motivation I will mention is in relation to psychiatric disorders. While conventional psychiatry tends to inaccurately depict psychiatric disorders as purely pathological and entirely genetic while ignoring environmental influences, and significant problems exist in current psychiatric practice, this has been taken by some as reason to completely deny genetic, endogenous origins of psychiatric disorders. Such individuals often point out that psychiatric disorders are not inherently diseases and the traits associated with them have benefits, however genetic denialism is actually contradictory to this idea - if psychiatric disorders are genetic, it suggests the genes that increase the "risk" of them have been selected for a reason, and this leads to a less pathologizing and more human view of psychiatric disorders (e.g., Nettle et al. 2006). It is also not suggestive that society should not accommodate for individuals with psychiatric disorders and change in such a way that allows individuals who are considered mentally ill to thrive - it should suggest the opposite.
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