This post is a review of The Social Genome: The New Science Of Nature and Nurture. By Dalton Conley. W.W. Norton & Company. 292 pp. $29.99.

A breakthrough in socio-genomics, the polygenic index (PGI) allows researchers to use DNA to quantify an individual’s genetic tendencies for physical, mental and behavioral outcomes, including height, diabetes, depression, schizophrenia, and educational attainment. Accurate within given ancestral populations and able to measure “the random shuffle of parents’ chromosomes,” PGIs, Dalton Conley, a pioneer in the field, points out, cannot explain differences between races or gender gaps. Nor can they determine with anything close to certainty what the future holds for a particular individual. Twelve percent of people from the bottom of PGI attainment and 60 percent of people at the top, for example, graduate from college.

In The Social Genome, an immensely informative book, Conley, a professor at Princeton University who holds doctoral degrees in sociology and biology, mounts what appears to be a compelling refutation of the conventional nature-nurture dichotomy while transforming our understanding of what shapes human behavior.

For most traits, Conley demonstrates, genes work through the environment. Some people are willing and able to seek out a particular environment or alter one they encounter. For others, war, poverty, discrimination and other factors prevent genes from taking full effect. The environment, moreover, differs from place to place and era to era. An aggressive genotype in the United States, Conley indicates, could propel a child of wealth into a penthouse and a poor youngster from a crime-ridden neighborhood into prison. Environmental factors that explain differences between children within the same family might include: random accidents; which teacher the child gets; the timing of parental divorce; how robust the economy was at graduation; whether or not the child was drafted into the army.

With respect to educational attainment (which includes genes for impulse control and cognitive ability), Conley reports, friends were as genetically alike as first cousins: “Our genes select our friends, their genes select us.” Half of the similarity is due to the social composition of neighborhood schools or admissions criteria.

Similarly, we choose spouses with phenotypes similar to ours. The couples then form an environment “that echoes back on us,” influencing how “our genes play out in the world.” Assortative mating in terms of socio-economic factors helps explain forty percent of the rise in inequality in the U.S. in recent decades and resurfaces in the genomes of the next generation. Parental intervention in the five years after a child is born pays tremendous dividends on test scores and graduation, wages, and criminal behavior. Interestingly, a child with a relatively high PGI for educational attainment gets more positive attention from parents than a sibling with a lower score.

Skin tone, Conley reminds us, is controlled by genes. Because of the stress stimulated by racial discrimination, African Americans with darker skin have higher blood pressure, on average, than Blacks with lighter skin. “It’s weird to think of that as a ‘genetic effect,’” Conley acknowledges, but it is in some respects no different “from the precocious child who gets put into advanced classes.” Perhaps, he hopes, PGI “can help us understand and get rid of these irrational biases.”

Conley concludes with reflections on the public policy implications of “the brave new world” of PGI. Ignoring genetic inequality, he indicates, isn’t going to make it go away. Nor will it refute “faulty neo-eugenic” arguments for monitoring the behavior of at-risk teenagers with risky genotypes. But Conley is concerned about allowing college admissions officers, employers, and insurance companies to use PGIs to practice statistical discrimination. And, of course, about the social implications of aspiring parents using PGIs to select sperm donors.

The good news, Conley emphasizes, is that “genes are not determinative” in the way most people think they are. And that genetic inequality can “gain or wane in importance” if the environmental landscape is altered through, for example, free early childhood education or a guaranteed basic income.

The window is now open, Conley believes, for constructive debate about socio-genomics. That said, he worries that “once PGI becomes a household word, shouting will replace dialogue.” But he hopes as well that “the fact that the line between nature and nurture is illusory will force a change in the way we view fairness.”

For every person who reads The Social Genome that hope is more likely to become a reality.