PRB

Two decades of research make it increasingly clear that both nature and nurture always play a role—that is, the extent to which genetic factors affect behavior depends on the social environment in which people live, work, and play.

Two recent studies show how individuals’ genes and their social environment interact to influence health and behavior, such as smoking, the friends they choose, and how much education they pursue.

We Are the Company We Keep

A recent article in the Proceedings of the National Academy of Sciences looks at new research on the roles of genes and the environment, focusing on whether an adolescent’s social and school networks had any influence on their height, weight, or educational attainment.¹

While researchers found no connection to height or weight, their analysis shows that the genetics of a person’s friends and schoolmates influenced how long they stayed in school, even after accounting for the individual’s genes.

The research team from University of North Carolina at Chapel Hill, Stanford University, Duke University, University of Wisconsin-Madison, Princeton University, and University of Colorado Boulder based their study on data from 5,500 adolescents in the National Longitudinal Study of Adolescent to Adult Health (Add Health), which surveys school populations and asks participants to name their friends.

It’s not just your genes, it’s the cumulative influence of your friends’ and classmates’ genes.

“We show that there is something about the genetic composition of one’s social group that has a positive influence on the individual,” says Jason Boardman of the University of Colorado Boulder, a study author. “It’s not just your genes, it’s the cumulative influence of your friends’ and classmates’ genes.”

According to Boardman, the most likely explanation for why classmates’ genes influence students’ educational attainment is what researchers call “evocative gene-environment correlation.” For example, certain genes increase the likelihood of children having an irritable temperament, which in turn evokes relatively harsh treatment from their parents. “Their genes create the environment to which they are exposed,” he says.

Similarly, says Boardman, teachers may respond positively to certain groups of students because of the way they collectively present themselves in the classroom—perhaps more compliant or more punctual with assignments—and that has an independent influence on all members of the group.

“A group of students may receive better treatment than others because of observable behaviors that have individual genetic origins but take on a social role because they evoke a positive response from the teacher,” he says. And this better treatment may contribute to higher achievement and those students staying in school longer.

Links Among Genes, Smoking, and Staying in School Are Stronger for Gen X and Millennials

A recent American Sociological Review article shows how environmental conditions influence when and how having specific genes may matter.² A team of researchers finds that the links among genes, educational attainment, and smoking are stronger among Generation X and early Millennials (born 1974 to 1983) than among Baby Boomers and their parents (born 1920 to 1959).

The team from University of Colorado Boulder, University of North Carolina at Chapel Hill, Stanford University, and Harvard University based their research on data from the nationally representative Health and Retirement Study and the Add Health study. They focused on participants of European genetic ancestry because researchers have identified genes linked to smoking and educational attainment in this population.

Earlier research identified sets of genes linked to single behavioral outcomes, including smoking and educational attainment. This study takes that line of research further by examining the relationship among those genes and whether a person smokes and how much education they received, focusing on differences across generations.

Americans with higher levels of education are less likely to smoke. This pattern is more pronounced among more recent generations, the research team finds, suggesting the process is driven by changes in the social environment.

Among the younger generations, “individuals who get more schooling are selected into environments where smoking is no longer acceptable, and therefore, they are less likely to smoke,” they write.

Social environment can shape the extent to which certain genes influence the association between behaviors.

Genes play a role in this changing relationship between education and smoking. People with certain genes linked to higher levels of educational attainment are increasingly less likely to have genes linked to smoking and to be smokers, reports Robbee Wedow of University of Colorado Boulder and the study’s lead author.

Over the past century, U.S. average educational attainment increased, smoking rates declined as the health hazards became well known, and more-educated people tended to smoke less. “The increasing genetic correlation between smoking and education that we found is mediated by increasing education—it reflects the role of increased education during the period,” explains Jason Boardman, a study author.

Their findings suggest that social environment can shape the extent to which certain genes influence the association between behaviors—in this case, the relationship between educational attainment and smoking, he points out.

“Studying human genetics divorced from an understanding of social mechanisms will produce misleading conclusions,” Boardman argues.

Research on the interaction between genes and social environments—called the social genome—holds implications for both genetics and the social sciences. For geneticists, these findings underscore the importance of considering the social context when studying the expression of genetic traits. For social scientists, it provides a more nuanced view of the impact of peers and social networks on individual behavioral choices.

This article was produced under a grant from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD). The work of researchers from the following NICHD-funded population research centers was highlighted in this article: Duke University, Princeton University, University of Colorado Boulder, University of North Carolina at Chapel Hill, and University of Wisconsin-Madison.