Charles Murray, Wall Street Journal, January 27, 2020
Almost all human traits are partly heritable. That’s been known for decades. But until a few years ago, no one knew what specific bits of DNA code determine any given trait. Now, however, geneticists have identified at least a few hundred variants in the DNA code that are statistically associated with important traits such as intelligence, depression and risk tolerance. Over the next decade, they are on track to identify thousands of variants associated with dozens of traits. That achievement will open up the ability to score genetic potential on those traits and thereby revolutionize the social sciences.
The methods of scoring are improving almost monthly, but the essence is simple. Each variant has a version (more precisely, one of the alleles in a single nucleotide polymorphism) associated with a small boost to the trait in question. If you add up those small boosts, you have a score for that trait, in the same sense that you have an IQ score if you add up all the correct answers to the questions on an IQ test. In the case of DNA variants, it is called a “polygenic score.”
Polygenic scores are revolutionary because they are causal in only one direction. They don’t drop because tests make you nervous or rise because you grew up rich. They’re impervious to racism and other forms of prejudice. Socioeconomic and cultural environments can play an important role in how those bits of DNA are expressed, but they don’t change the codes themselves. That means polygenic scores will offer social scientists something they’ve never had before: a secure place to stand in assessing what is innate and what is added by the environment.
I have presented an optimistic view of the coming genomic revolution. Some prominent scholars adamantly disagree. They argue that science is about understanding causal pathways. Complex social behaviors such as marriage and divorce are known to be partly heritable but they do not have a specific genetic etiology. In the words of one of the leading pessimists, psychologist Eric Turkheimer, causal explanations are not going to be found in individual bits of DNA “any more than explanations of plate tectonics can be found in the chemical composition of individual rocks.”
I think the application of genomic data to social science questions is roughly where aviation was in 1908. The world’s best plane, the Wright Flyer, was little more than a toy. Yet within a decade, thousands of acrobatically maneuverable aircraft were flying high and fast over the battlefields of Europe.
The history of science allows one more prediction. When a scientific discipline gets a major new tool—such as the microscope or spectrometer—its eventual uses sprawl far beyond its original ones. Polygenic scores will be a similarly multipurpose tool, with open-ended potential for finding answers to questions today’s social scientists can’t even imagine.