Just had an interesting conversation around a post about the results of their genetic test, specifically whether a specific gene (COMT) implies a specific personality or general behavioral phenotype (“Warrior”). In the course of the conversation, it was implied that behavior is “significantly” driven by genes, that complex behavior is heritable, and that environmental effects are possibly overstated with regard to behavior. Specifically the statement was offered that adverse childhood events somehow are less impactful on behavior than DNA (with regard to “ADHD”).
The support for this was largely that twin studies show “heritability” of particular behavioral traits.
Okay so let’s take a slight detour into the realm of twin studies. First, no twin study has ever revealed any unique behavioral presentation that wasn’t already what was being searched for. We’ve never had a twin study which revealed something like this person with this gene reacts in this particular way to this stimuli after controlling for SES. Not a single supposed behavioral trait. If our understanding of heritability of behavior was in any way accurate, this is exactly the type of result we’d excel at using twin studies.
With our twins as a base and the world as our control, finding these unique behavioral traits would be as simple as finding unique alleles if behavior was a pure artifact of DNA. In a world of massive indexing and computing power, we can easily search through millions of individuals in seconds to verify if trait x results in behavior y. Despite this, outside of a few syndromic conditions like Williams Syndrome (which I’d argue are perception differences rather than behavioral), there are no causal connections between specific expressed behavioral traits and alleles.
Worse, the assertion that twin studies attempt to make aren’t about trait expression, but heritability of a supposed behavioral trait. And this supposed heritability of a behavioral trait is argued as both the trait itself is an actual fixed behavioral trait is valid (particularly cross-culturally), but that the trait itself is guiding behavior. Neither of these are supported assertions!
We have LOTS of data, twin studies searching for behavioral traits aren’t exactly rare or recent. They formed the basis of Galton’s eugenics proposals, every trait superiorist ever including great guys like Mengele have advanced the construct, and yet after 150 years of riding these ideas there’s no gene test in the world which can identify any specific behavioral trait in any individual. It feels like astrology, yeah you’re an Aquarius with these particular behavioral traits, except that most Aquarius don’t and it’s because they have some other sign in some other house. When it doesn’t work, obfuscate.
“Autism” and the research surrounding it ties nicely here because the most comprehensive twin studies, in addition to largest population sizes we have in the search for behavioral traits, heritability, and genetics has been generated by this field over the last few decades. Is there a genetic test for “Deficits in social-emotional reciprocity”? How about “Restricted, repetitive patterns of behavior” (sounds like going to work)? Maybe “Highly restricted, fixated interests that are abnormal in intensity or focus”? How granular do we have to get with these supposed behavioral presentations to find anything? We’re staring right at it, seeing heterogeneous results, and… ignoring it to keep chugging down the same path?
We furthered this throughout the 20th century doing extensive work examining prisoners or other social malcontents for specific traits that supposedly lead to their criminality. We’ve tested everything from genes to cortisol to find what makes the criminal tick. So… what makes the criminal tick?
So we can’t find simple behavioral traits, we can’t find complex behavioral traits, but trust me bro, the genes are more important than environment? We are still trying to push “weak/strong genes” over SES?
I’m still waiting for studies on the heritability of “conservatism” or “hair twirling”. Maybe video game preference, or average length of time to achieve orgasm. The entire concept of strong genetic behavior is just so in eugenic “strong/weak” concepts that we can’t even think to test outside of them.
Do genetics influence behavior? Being 7ft tall and agile means society is more more likely to bias you toward activities that value those trait expressions. Are some behavioral traits heritable? Sure, simian reflex is real. But if we strip out the influence of SES, Tarzan behaves like a wild child and not the distinguished British gentleman his genes supposedly dictate.
And this is the core of the argument regarding genetic influence on expressed behavior, is it even possible to separate the social influence? When is a gene for “ugly” also a gene for “shy” or “depressed”? Probably way more frequently than even monochorionic twin behavioral associations.
The over-association of genes with behavior through twin studies is a pretty classic example of internal vs. external validity, while the associations we derive from this field can replicate and demonstrate internal validity, when we force them to be checked against external constructs, all of our supposedly statistically massively unlikely to be defeated null hypothesis blow up really quickly.
Our genes provide a substrate for the environment to act upon, and it is that environmental effect which ultimately drives expression of any particular gene or behavior.