Do Genes Directly Affect Human Behavior?

DNA double helix horizontal.png by Jerome Walker, Public domain

One thing that I have complained about over the years is the tendency of many biological psychiatrists to misread the science to way over-emphasize genetic causative factors of repetitive problematic behavior - susceptible to treatment with drugs - and way under emphasize causative environmental factors - for which psychotherapy would be the preferred treatment.

A recent study  in Translational Psychiatry (Aug 2026) illustrates the problem. It showed that patients with social anxiety disorder shared genetic risk factors with several major psychiatric illnesses, including schizophrenia, bipolar disorder, and depression. The study looked at polygenic risk scores, not just one or two genes. Shared genetic factors were not associated with disease severity or common clinical subtypes.  And the observed effect sizes were generally small.  The article did not specify, but I suspect that, additionally, some of their cases of social anxiety may have not shared many of these genetic risk factors, while control subjects may have.

Social anxiety disorder is hardly the only psychiatric diagnosis that commonly shares genes with other psychiatric illnesses. Almost all of them do! This make it even more ironic that many nurse practitioners and even quite a few psychiatrists seem to add on a new drug as soon as a patient exhibits any new symptoms. Anxiety and mood symptoms are naturally at the top of the list, but subjects often have co-occurring symptoms of several other behavioral disorders like these subjects did: schizophrenia, bipolar disorder, and even anorexia nervosa. 

Any one gene is not necessary or specific in predicting the vast majority of psychiatric disorders.

This is not to say that in some cases an addition of medication to psychotherapy is never required. I remember seeing a study that showed that 40% of subjects diagnosed with borderline personality disorder met full criteria for panic disorder. (It was higher percentage than that in my clinical practice). Patients often did not disclose these symptoms unless specifically asked, and I did. 

Furthermore, a panic attack seemed to occur immediately before the patients engaged in self-mutilation like cutting. If the panic disorder was adequately medicated, the self-injuring behavior often disappeared. MUCH more quickly than with a course of dialectical behavioral therapy.

But what I observed was that patients previously treated by a mental health practitioner were coming to me on a whole medley of different psychoactive med. Sometimes they cancelled each other out. Like I always say, “Uppers and Downers and Bears! Oh my!"

Several companies also offer to look at a client's genetic makeup to predict which antidepressant is most likely to work for them. When I tried these tests, they were for the most part not useful clinically. I did a better job of predicting which antidepressant to start out with than these tests.

Genes do affect human behavior in a variety of ways, but as Robert Sapolsky points out in his book Behave, each of them only makes certain responses a little more or a little less likely. They don't determine it any further than that. And this applies to normal human brains, not just diseased ones.