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February 26, 2019

A blueprint in our genes for behavior?

Filed under: Eugenics,Genetics,Personality,Psychology — Razib Khan @ 4:44 pm

Since the emergence of the field of genetics over a century ago the question of “nature vs. nurture” has loomed large over the field when it comes to the nature of “human nature.” The very term “human nature” is a tell as to its origins and early connotations: the early idea was that we are “born that way.” Society was seen to have a hereditary basis, as was your own individual life outcome.

It is true that in the early decades of genetics, researchers were preoccupied with fruit flies, pedigrees, and equations. But genetics was not alone on the scene. Eugenics, a social and cultural movement which presented itself as an application of hereditary science to improve the human race, developed in the same decades to great public aclaim. One of the founders of the field of statistical genetics, Francis Galton, was also the founder of eugenics!

Though the history books tell us about the history of eugenics with the shocking culmination of the horrors Nazi Germany, the fact is that the nation which arguably took up eugenics most enthusiastically in the decades before World War II was the United States of America! This was a period when socialists such as H. G. Wells, and conservatives such as Winston Churchill, both supported eugenics. The German Nazis modeled many of their policies and laws on American precedents.

It is in the context of this history that the branch of psychology dealing in heritable individual differences, behavior genetics, slipped into the shadows in the decades after the defeat of the Nazis. The nature of heritability of behavioral characteristics was somewhat taboo because they had been the subject of fascination by eugenicists. Genetics generally restricted itself to healing terrible diseases. When it comes to other aspects of mind and body it receded. For example, Freudianism and Behaviorism were more common perspectives brought to bear on individual differences and outcomes in psychology. Though these perspectives did not reject biological inheritance as such, they focused on environmental inputs and outputs.

Schizophrenia was seen as a disease of upbringing or environmental exposure. Not one of genetic transmission from parent to offspring (today we know that schizophrenia is 80% heritable!).

This situation began to change with the emergence of a field of cognitive science which held that some aspects of psychology were innate, such Noam Chomsky’s theory of universal grammar, which implied a biological underpinning for our facility with language. And, just as some psychologists were exploring the inherited bases of our universal behaviors and aptitudes, others began to look more closely at differences. Human variation.

The reemergence of behavior genetics, the study of individual differences, and the attempt to infer both the environmental and genetic components of various outcomes evolved in the context of large longitudinal studies of twins and their siblings. The logic here is simple: the correlation in a characteristic such as height between identical twins is nearly perfect. For siblings (and fraternal twins), there is a correlation, but it is far weaker because sibling relatedness is only 50%. If the correlation on a behavioral trait, such as the likelihood of schizophrenia, is correspondingly greater between identical twins than between their siblings, then it is highly heritable. Genes play a large role in the trait’s expression. In contrast, if there is no difference between twins and how siblings correlate on a trait, then that suggests that there is not much of a genetic basis to the characteristic. Recall, identical twins by definition are more genetically related than two siblings.

There are of course many theoretical objections to twin studies (e.g., perhaps parents treat twins more similarly than they do siblings), and the statistical abstruseness of behavior genetics means that its implications and findings did not get broad coverage as the field matured in the late 20th century. Despite several decades of research, by the year 2000, it is likely most people were not aware of the substantial heritability of many behavioral and psychological characteristics, from personality disposition to mental illness.

The last few decades have changed this, in part because the new science of genomics, which looks beyond statistical correlations of characteristics to raw DNA sequence, has begun to merge with behavior genetics. Because psychological characteristics were almost always defined by the small effect of many numerous genes classical genetics did not have the power to locate any genes that were involved in psychological variation. But with massive sample sizes of as much as a million and hundreds of thousands of genetic positions, new research is now confirming the statistical work from twin studies that many psychological characteristics are substantially heritable.

Illumina Sequencer

The study of human nature and our differences and the possible genetic causes of them began with a tragedy and a travesty. Eugenics marred the legacy of many early geneticists, and its application in the United States and Nazi Germany were crimes against humanity. But as the 21st century proceeds the study of human psychology and its genetic basis is now becoming a true science. Able to describe, as well as predict.

But, it turns out its powers of prediction are quite modest, far less than any eugenicist would have foreseen or dreamt of. The truth is a genetic test can give you only a small improvement on your odds of knowing the likely track of your life. And perhaps that is for the best.


A blueprint in our genes for behavior? was originally published in Insitome on Medium, where people are continuing the conversation by highlighting and responding to this story.

November 11, 2011

Personality and genes

Filed under: Behavior Genetics,Genes,Personality — Razib Khan @ 6:10 am

There’s a variable in the GSS, GENEEXPS, which asks if genes play a role in personality. The options are:

- It’s genes which play a major role

- It’s experience which determines personality

First, let’s admit that the premise is stupid. Personality is heritable, but environmental variation also seems to matter. In other words it is noncontroversial to assert that both genes and environment can explain variation in personality (or perhaps more precisely genetic variation can only explain around half the variation for any given trait).

I was curious how this broke down by education and intelligence. To remove demographic confounds I limited the sample to non-Hispanic whites. For intelligence I used WORDSUM, with scores 0-4 being dumb, 5-7 being average, and 8-10 being smart.



Genes play major role Experience plays major role
Less than HS 33 67
High School 26 74
Junior College 26 75
Bachelor 21 79
Graduate 24 77
Dumb 25 75
Average 25 75
Smart 24 76


May 6, 2011

How the “fierce people” came to be

The pith: there are differences between populations on genes which result in “novelty seeking.” These differences can be traced to migration out of Africa, and can’t be explained as an artifact of random genetic drift.

I’m not going to lie, when I first saw the headline “Out of Africa migration selected novelty-seeking genes”, I was a little worried. My immediate assumption was that a new paper on correlations between dopamine receptor genes, behavior genetics, and geographical variation had some out. I was right! But my worry was motivated by the fact that this would just be another in a long line of research which pushed the same result without adding anything new to the body of evidence. Let me be clear: there are decades of very robust evidence that much of the variation in human behavior we see around us is heritable. That the variation in our psychological dispositions, from intelligence to schizophrenia, is substantially explained by who our biological parents are. This is clear when you look at adoption studies which show a strong concordance between biological parents and biological children on many metrics as adults, as opposed ...

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