Dalton Conley is a professor at Princeton University and author of the recent book The Social Genome (2025). This is a fascinating book with many interesting facts (did you know that the average married couple is as close genetically as if they were first cousins once removed?) and an overall message that raises interesting and difficult ethical questions. Hence, this blog post.

For seemingly forever, there has been a “nature vs. nurture” debate focusing on whether our genes or our environment has the larger impact on our lives—our flourishing and faltering. Conley is a founder and leader in the field of sociogenomics, which he defines as “the application of genetic data to human behavior to gain a more complete picture of nature and nurture.” (p. 19) With the advances made by the Human Genome Project, CRISPR, and other research, scientists have new knowledge at their disposal that is relevant to this debate (though there’s much left to learn).

Genes are clearly very important. Most traits and diseases are polygenic, in that they are influenced by combinations of many, perhaps thousands of genetic differences. Though it is still relatively early days in the field, scientists can study your DNA and produce a polygenic index (PGI) for you—a single number that summarizes your genetic tendency for, say height, blood pressure, depression, BMI, diabetes, educational attainment, and many other features. This number is no guaranteed predictor of the future of any single person, but experience shows that someone who is in the bottom 20% of the PGI ranking has only a 12% chance of completing college, whereas someone in the top 20% has a 60% chance. That the PGI is so far from 100% accuracy indicates the importance of nurture in the equation.

Conley’s research shows “that there is no clear line between what we call genetic and what we call environmental. It turns out that part of nurture is nature, and that part of nature is nurture. The social genome deletes the versus.” (p. 19) This makes sense when you think about it. Height has been widely studied. How tall you are is determined mostly by your genes. Attractiveness is largely determined by genetics, though not as much as height. But people who are tall or attractive, or both, have scored a little win in the genetic lottery. They will tend to be favored as romantic partners, employees, even as students in elementary school. Evidence indicates that students who are tall and/or attractive will be more likely to be labeled as “gifted” and more likely to receive extra attention from teachers. And from their parents. Thus, their nature will give them a leg up in the nurture department.

These students received their genes from their parents, of course, but the parents’ genes—let’s say one or both have genetic predispositions to addictive behavior—might well significantly shape the environment that the students experience at home. Again, nature affects nurture.

And nurture similarly can and does affect nature. Joe and Mary may have similar PGIs for educational attainment, indicating they both have the cognitive ability, drive, impulse control, and other genetically-determined features that make it likely that they can complete a college degree. But if Joe’s parents are wealthy and college-educated themselves and his older sibling has already graduated from college, Joe will have a better chance of nabbing that college degree than Mary who was raised in a different environment—one of penury and parents who are not educated themselves and do not see the point of a college degree and with an older sibling who dropped out of high school. Nurture again affects nature. Conley says:

“…much of what we think of as nature works through the environment, while much of nurture might be best called ‘genetics one-degree removed’ since the DNA of the important people in our lives constitutes much of our social environment.” (p. 19)

Most of Conley’s book is devoted to spelling out the many ways (passive gene-environment correlation, evocative gene-environment correlation, homophily, assortative mating, gene-by-environment interaction effect, and other influences the book will introduce you to) in which ours (and others’) genes affect our environment and our environment affects our genes. There is a constant “tango” between the two.

As we write this post, it is coming to light that scientists have used CRISPR technology to create a breakthrough bespoke genetic treatment for a baby (“KJ”) born with a rare genetic disease. That’s fantastic news. But equality, which he has studied his entire academic career, is on Conley’s mind. Inequality, including genetic inequality, has been growing over the years. Conley cites demographer Christine Schwartz who believes that increasing assortative mating (high-earning men and high-earning women increasingly marrying each other) is responsible for as much as 40% of the recent substantial increase in income inequality. This is concerning.

Hitler and his Nazis have given eugenics a bad name in most circles. But what about a little gene editing? Conley is sympathetic to bioethicist John Evans’ view that modifying our offspring’s DNA dehumanizes children. They are no longer individual human beings, they are “objects in a game of attainment.” (p. 218)

Conley and colleagues have surveyed Americans and found that the vast majority think it morally wrong to judge people based on their genes at conception. But consider these questions:

  1. Sally is looking for a sperm donor and choosing between Nate and Adam. Is it moral for her to check out their PGI scores to make that choice?
  2. Bo is looking for a serious relationship and has just met and been attracted to Tinisha and Barb. Is it moral for Bo to check their PGI scores to decide whom to pursue as a potential spouse?
  3. Diane is about to have an embryo implanted with hopes of having a child. Is it moral for Diane to choose between two available embryos by checking their PGI scores on certain important dimensions?

Conley’s survey respondents approve of all three uses of PGI scores (at rates of 83%, 79%, and 68%, respectively), surprising and not particularly pleasing Conley. He notes that checking PGI scores should reduce the disease rate in future generations, much as screening for Down’s syndrome now does. On the other hand, companies are going to want to make money offering these services and wealthy people will likely, as usual, be first in line to take advantage of them, push[ing] us even further toward a caste-like society in which our high level of socioeconomic inequality is baked into the genes of the next generation.

These are issues that Americans and their policy makers will have to address.  They should read Conley’s book before they do.

Sources:

Dalton Conley, The Social Genome: The New Science of Nature and Nurture (2025).

Dalton Conley & Justin Fletcher, The Genome Factor: What the Social Genomics Revolution Reveals about Ourselves, Our History, and the Future (2017).

John H. Evans, The Human Gene Editing Debate (2020).

Carolyn Johnson, “How a Race to Create a Drug for One Sick Baby Made Medical History,” The Washington Post, May 15, 2025, at https://www.washingtonpost.com/science/2025/05/15/crispr-gene-editing-breakthrough/.

Christine Schwartz, “Earnings Inequality and the Changing Relationship between Spouses’ Earnings,” American Journal of Sociology, Vol. 115, No. 5 (March 2010).

Kate Zernike, “What if We Selected Ourselves Out of Existence?” New York Times, March 23, 2025 (book review), at https://www.nytimes.com/2025/03/23/books/review/the-social-genome-dalton-conley-the-decline-and-fall-of-the-human-empire-henry-gee.html.

Videos:

In-group/Out-group Bias: https://ethicsunwrapped.utexas.edu/glossary/in-group-out-group

Halo Effect: https://ethicsunwrapped.utexas.edu/glossary/halo-effect