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High rMZ by itself does not mean a trait is "genetic." That's why behavioral geneticists compare rMZ to rDZ, assuming that both twin environments are "equal." Because they are not equal, twin studies of behavior provide no valid evidence in favor of genetics. Eric T. and I differ on this point.

"Heritability" is an animal breeding statistic that behavioral genetics has falsely extended into a measure of the strength of genetic influences. Whether or not genes influence a trait, the "heritability of behavioral trait X" has no meaning. Heritability cannot be "missing" if it doesn't exist.

The point is that twin studies have been misinterpreted for 100 years. The results can explained by environmental factors. Combined with the misleading heritability concept, the key point is that, at least in behavioral areas, the meta-analysis tells nothing about genetics or nature-nurture splits.

KPH blocked me several years ago when I questioned the value and assumptions of twin research.

He was following the eugenic genocide playbook initiated by Francis Galton, and continued by psychologist Raymond Cattell in his 1972 book "Beyondism." He called for "phasing out" genetically "moribund cultures." The Am Psychological Association tried to give Cattell a "Lifetime Achievement Award."

Respectfully, twin studies do not "report" anything. Researchers are the ones who report, and their genetic interpretations of twin data rest on several unsupported assumptions. In the 1990 Minnesota study, the researchers suppressed their (DZ-apart) control group data to reach desired conclusions.

"Acknowledging genetics is not endorsing eugenics!" As a critic of the behavioral genetics (BG) field, I agree. Still, the evidence Harden cites in support of genetics is based on BG research, and non-causal GWASes and polygenic scores. In other words, no evidence at all. A truly forgettable book.

There is very little in Harden's book about how the massive inequality, poverty, racism, union busting, etc., strongly contribute to U.S. crime rates. Not to mention the subjective aspects of certain crimes. Who hasn't done something illegal at some point in their life? A forgettable book.

Critics don't need to invoke eugenics to understand that Harden's new book contains a dull rehash of massively flawed BG research (eg, twin, adoption, DNA-based), which she claims as "science." I don't care about her personal journey, other than that it led to a dead end called behavior genetics.

@ent3c.bsky.social examined the OP author's earlier gene discovery claims and concluded that they do not hold up. www.madinamerica.com/2025/04/fail...

The Failure of “Spit For Science”: No Genetic or Neurological Pathways for Substance AbuseDespite finding no meaningful correlation between genes and substance use, high-profile geneticists misleadingly conveyed optimistic results.www.madinamerica.com

Probably more informative that most human behavior and psychiatric GWASes. And at least in this case, in contrast to the above, the methane “phenotype” is a reliably measured valid construct.

The Nazi/"racial hygiene" origins of psychiatric genetic research have also been whitewashed. pubmed.ncbi.nlm.nih.gov/23180223/ www.madinamerica.com/2015/10/erns...

The answer is extraordinary simple. There are no causal “genes for schizophrenia. “ EF Torrey discussed schizophrenia DNA-based research as a search for a “psychiatric yeti.” Torrey was right.

A good 2025 article by Peter Simons of @mad-in-america.bsky.social describing how genetically oriented researchers keep beliefs intact by claiming behavioral gene discoveries that are not real (not to mention the earlier 25-year-long "candidate gene" era flop). www.madinamerica.com/2025/04/fail...

The Failure of “Spit For Science”: No Genetic or Neurological Pathways for Substance AbuseDespite finding no meaningful correlation between genes and substance use, high-profile geneticists misleadingly conveyed optimistic results.www.madinamerica.com

Inspired, in part, by the founder of the psychiatric genetics field, Ernst Rüdin, and his followers in the "Munich school" of psychiatric genetics. At that time, it was the only school of psychiatric genetics. bsky.app/profile/jayj...