madinamerica
Dr Jay Joseph
Dec 18. 2018
[excerpt]
https://www.madinamerica.com/2018/12/twin-studies-prove-nothing-genetics-psychiatric-disorders/I write frequently about the fallacies of behavioral twin research, in both its “reared-together†and “reared-apart†forms. I am compelled to keep doing this because twin studies of behavior, and the claims based on them, have not gone away despite decades of critics’ airtight arguments that indicate that they should have gone away a long time ago. Assessing the validity of psychiatric twin research is very important because it relates directly to the question of whether the main causes of psychological distress and dysfunction, and socially disapproved behavior, are located inside of the human body and brain, as mainstream psychiatry claims, or outside of the body and brain, as many critics argue. Twin studies are often cited in support of psychiatry’s disputed claim that its diagnoses are valid medical/biological conditions caused by a brain malfunction or by a “chemical imbalance.â€
I recently published an online in-depth critical analysis of the famous “Minnesota Study of Twins Reared Apart†(MISTRA), where I concluded that because this “reared-apart†twin study was unable to disentangle (separate) the potential influences of genes and environments on human behavior, in addition to many other reasons, the researchers’ conclusions in favor of important genetic influences on IQ, “personality,†and other behavioral characteristics must be rejected. This conclusion applies to all other published “twins reared apart†studies as well. Other than some individual cases of MZ pairs that have come to the attention of researchers since the 1920s, the only reared-apart twin study that looked into areas related to psychiatry was a 1990 MISTRA study of substance abuse/dependence and antisocial personality.
Twin studies of the major psychiatric disorders have been based on pairs who were reared together in the same family home. Since 1998 I have written about the many problems with these studies, which nevertheless form the bedrock of genetic theories and claims in psychiatry. Here I will highlight and examine the main underlying fallacy of psychiatric twin studies, and of twin studies of behavior in general. It is now widely understood that psychiatric family studies are unable to disentangle the potential influences of genes and environment, because behavior can “run in the family†due to shared environmental factors. Psychiatric adoption studies are also cited in favor of genetic influences, but critics have pointed to many major problems and biases in these studies.1
