DEGREE of CONTRAINT
We’ve all heard the sentence that ends conversations: “ADHD is highly genetic.”
It’s usually said with the same finality as “gravity is non-negotiable,” as if someone has found the ADHD gene, laminated it, and hung it on a wall in a lab somewhere. And then—almost without noticing—people quietly translate in their heads: highly genetic → inevitable.
That translation is the problem.
Twin studies and GWAS do something genuinely useful: they tell us there is a real genetic signal. But they do not say what most people think they say. They don’t tell you an outcome is fixed. They tell you outcomes are constrained. Those are not synonyms. They’re not even close.
Here’s the clean distinction. Genetic determinism is the idea that genotype determines phenotype as if it were fate. Genetic constraint is the idea that genotype shapes the range of possible developmental pathways, without selecting a single endpoint in advance. If you confuse these two, you start seeing the world as a fixed game. If you separate them, you see something more accurate and, frankly, more interesting: outcomes arise over time through gene–environment interaction, in bodies that get tired, inflamed, underfed, overstimulated, soothed, supported, stressed—and occasionally—given room to recover.
The irony is that the genetics revolution hasn’t made psychological traits more deterministic. It’s done the opposite.
The more we learn, the less binary the system looks.
So why do so many intelligent people still talk as if heritability is destiny?
Because most of us—professionals included—are trained on the binary Mendelian genetics. Gene → trait → outcome. It’s clean, teachable, and makes for tidy exam questions. Even when we learn about polygenicity, we often keep the same mental…