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The Behavioral Genetics Page


This page is to make an easy to use (and share) central repository for my posts on the science of behavioral genetics. This is fundamental reading for anyone interested in HBD, and I’d say the human sciences in general.

All Human Behavioral Traits Are Heritable – This post introduces readers to the world of behavioral genetics and the concept of heritability. Introduces the “Three Laws” of behavioral genetics (the title of post being the First Law verbatim). Explains the value of twin and adoption studies to partition the sources of human trait variation – that is, disentangle nature from “nurture.” Shows that the source of human differences can be broken into three basic parts, heredity, the shared (or common) environment, and the “nonshared”/unique environment. Details that all human traits show heritable contribution (hence the First Law). Also details the lack of effect for shared environment for almost every human trait, which rules out nurture (as its commonly thought) and parenting of having a significant impact on life outcomes. Notes the huge impact the First Law has for human group differences. (Indeed, while not quoted in the post, by as John Derbyshire put it, ““if dimensions of the individual human personality are heritable, then society is just a vector sum of a lot of individual personalities.”)

Environmental Hereditarianism – Following up my preceding posts on the matter, this one delves into the matter of the “environment” in more detail. Specifically, this touches on commonly claimed “environmental” influences and explains why they are mostly bunk. As well, this analyzes the “unique environment” and explain why it’s not really environment at all – but more accurately, the “unexplained variances. Discusses some of the limitations of behavioral genetic tests that cause them to overestimate the effect of the environment and underestimate the effects of heredity – most significant among them being measurement error. Details the concept of developmental noise, noting how some of the variation between people (as seen in the differences between “identical” twins raised together) can be due to subtle disturbances during development (fingerprints being a simple example).

The Son Becomes The Father – Features the work of Gregory Clark, who (through surname analysis) shows that we evidence for heritability going back many centuries. I take the opportunity to detail larger, newer behavioral genetic studies that show high heritability for all human behavioral traits – including intelligence, personality, political views. As well, I should detail evidence showing high heritability for major life outcomes, including criminality, marital stability, drug use, lifetime income, and life satisfaction. More importantly, I detail the lack of shared environment effect for all of these traits. This is key to silencing critics who would like to place “nurture” as important in shaping who we become.

More Behavioral Genetic Facts – Here I analyze the some of the last-ditch efforts to insert “environment” into life outcomes, demonstrating the usefulness of reared-apart twin studies, as well the role that the informant/measurement method has on results. I also delve into the “extended twin design”, which looks at additional family members beyond twins to partition out further uncertainties in genetic vs. environmental influence (for one, this puts the kibosh on the notion that we choose spouses who resemble our opposite sex parent). I also touch on why peers are not likely a source of lasting influence. As well, I make a case against the importance of gene-environment correlations as a source of influence (itself a massive violation of Occam’s Razor).

In addition to these, be sure to read the papers collected at my HBD Fundamentals page, section On the science of behavioral genetics.

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