Tag: twin studies
This is the schizophrenia game. It has been played for over a century, and it’s time to stop.
Behavioral genetic “discoveries” are a mirage, a house of cards that ignores contradictory evidence from countless real-world examples and research findings from other fields, that collapses under serious critical analysis.
Although Mitchell and Murray cited twin studies as the main source of evidence in support of their claims, these studies are based on a long-controversial assumption which they were unable to defend in their books, or on Twitter.
Supporters of the nature (genetic) side of the “nature versus nurture” debate often cite studies of “reared-apart” or “separated” MZ twin pairs (identical, monozygotic) in support of their positions. In this article I present evidence that, in fact, most studied pairs of this type do not qualify as reared-apart or separated twins.
Three Identical Strangers is a riveting film describing the story of identical triplets separated at six months of age and reunited in early adulthood. Their story provides no evidence in support of the genetic side of the nature-nurture debate, but it does supply some evidence in favor of the environment.
Assessing the validity of psychiatric twin research is important because it relates to the question of whether the main causes of psychological distress and dysfunction are located inside of the human body and brain, as mainstream psychiatry claims, or outside of the body and brain, as many critics argue.
The time has come to halt the massive failure that has characterized schizophrenia molecular genetic research, and to thoroughly reassess what critics have always said are the severely flawed family, twin, and adoption studies that inspired and helped justify this research.
In his 2016 book The Gene: An Intimate History, cancer physician and researcher Siddhartha Mukherjee chronicled the initial idea of the gene, taking readers through the history of genetics up to the current “post-genome” period by interweaving science, social history, and his own personal narrative. In the process he documented some of the crimes of the eugenics movement and the monstrous atrocities committed by German National Socialism in the name of eugenics and biology, while noting the Nazi’s promotion of twin research. He also criticized aspects of intelligence testing and genetic theories of racial inferiority based on IQ tests. At the same time, Mukherjee supported and promoted many contemporary behavioral genetics positions.
The wealthy, and the institutions they finance and promote, look favorably upon research whose authors claim that economic disparities are rooted in biology, and are not harmful to humanity as a whole. But there are countless obvious real-world examples showing that political policies, social struggles, and public health programs, including those involving the adjustment of income differences, lead to improved health and well-being.
The March 3rd, 2016 edition of the Wall Street Journal featured an article by past President of the American Psychiatric Association (APA) Jeffrey Lieberman and his colleague, computational neuroscientist Ogi Ogas. The article was entitled “Genetics and Mental Illness—Let’s Not Get Carried Away.” In their piece, the authors started by expressing the belief that a recent study identified a gene that causes schizophrenia, and then discussed whether it is desirable or possible to remove allegedly pathological genes in the interest of creating a future “mentally perfect society.” The authors of the article, like many previous textbook authors, seem unfamiliar with the questionable “evidence” put forward by psychiatry as proof that its disorders are “highly heritable” In fact, DSM-5 Task Force Chair David Kupfer admitted that “we’re still waiting” for the discovery of “biological and genetic markers” for psychiatric disorders.
In this article I will attempt to debunk one of the great “scientific” smoke and mirrors shows of the past half century—the claim that stories of reunited separated MZ (monozygotic, identical) twin pairs indicate that heredity plays a major role in causing human behavioral differences. These stories, which are often used to sell the false ideology of genetic determinism, have entered the public imagination in a way that academic research results never could. Here I will show that these stories provide no evidence whatsoever that (as yet undiscovered) “genes for behavior” influence human behavioral development.
“The substantial hereditary component in schizophrenia,” a pair of researchers wrote in 1993, “is surely one of the two or three best-established facts in psychiatry.” But is it really? For mainstream psychiatry and psychiatric genetics, schizophrenia is “a severe mental disorder with a lifetime risk of about 1%, characterized by hallucinations, delusions and cognitive deficits, with heritability estimated at up to 80%,” or a “highly heritable neuropsychiatric disorder of complex genetic etiology.” Many commentators have challenged these claims, and some have challenged the concept of schizophrenia itself.
Although it is axiomatic in psychiatry that genetic factors are involved in bipolar disorder (manic-depression), and that they play a predominant role, there currently exists little if any scientifically acceptable evidence that bipolar disorder and other “affective disorders” are caused by disordered genes. Given almost 50 years of gene discovery claims that were not confirmed by replication attempts, we must assume by default that current gene finding claims are false-positive results as well. In the 1920s, pioneering psychiatric geneticist Ernst Rüdin decided against publishing his large family study of “manic-depressive insanity,” most likely because the results did not fit his theories of Mendelian inheritance, and failed to support his advocacy of eugenic policies.
Human behavioral genetics and its allied field of psychiatric genetics are in trouble, as unfulfilled gene discovery expectations during the “euphoria of the 1980s” have continued to the present day, leading to researchers’ “nonreplication curse” dysphoria of the 2010s. In my recent book The Trouble with Twin Studies: A Reassessment of Twin Research in the Social and Behavioral Sciences, I presented a detailed argument that genetic interpretations of the common “classical twin method” finding that reared-together MZ twin pairs resemble each other more (correlate higher) for behavioral characteristics than do reared-together same-sex DZ twin pairs are invalid because, among other reasons, the twin method’s crucial MZ-DZ “equal environment assumption” (EEA) is false.
In 2000, behavioral geneticist Eric Turkheimer proposed "Three Laws of Behavior Genetics" based on what he saw as the “nearly unanimous results” of behavioral genetic studies of families, twins, and adoptees. However, critics have argued for decades that most behavioral genetic assumptions, models, concepts, “laws,” and “discoveries” do not hold up under critical examination. In 2015, a group of behavioral geneticists proposed an additional “Fourth Law of Behavior Genetics,” which states that behavioral characteristics are associated with many genes of small effect. Here I propose a “Fifth Law” of behavior genetics—actually, the only “law” one needs to know in order to properly understand this field.
The long-running debate on the validity of twin research recently resurfaced in American criminology, and has major implications for behavioral and medical twin research. Most twin researchers and their critics agree that reared-together monozygotic (MZ) twin pairs experience more similar environments than experienced by same-sex dizygotic (DZ) pairs, and we argue that the twin method is therefore unable to disentangle the potential influences of genes and environment on human behavioral differences, a conclusion supported by the failures of molecular genetic research.