Effects of the peer metagenomic environment on smoking behavior


Sotoudeh, Ramina; Harris, Kathleen Mullan; & Conley, Dalton (2019). Effects of the peer metagenomic environment on smoking behavior. Proceedings of the National Academy of Sciences. vol. 116 (33)


Metagenomic or social genetic effects—how the genetic makeup of organisms around an individual impacts an individual’s phenotype—have been demonstrated for animals. However, in humans, where experimental manipulation is less feasible, such metagenomic effects of peers have largely been suggestive. Here, we leverage as-if-random variation in same-grade peers to document metagenomic effects on adolescent smoking outcomes. The effect of grade-mates’ genotypes is larger in magnitude than many other predictors of smoking, including ego’s own genotype, being male, and family income. Further, a minority with high genetic propensities to smoke can affect the smoking behavior of an entire grade. This approach offers a way to integrate genetic and environmental influences on human phenotypes.Recent scholarship suggests that the genomes of those around us affect our own phenotypes. Much of the empirical evidence for such “metagenomic” effects comes from animal studies, where the socio-genetic environment can be easily manipulated. Among humans, it is more difficult to identify such effects given the nonrandom distribution of genes and environments. Here we leverage the as-if-random distribution of grade-mates’ genomes conditional on school-level variation in a nationally representative sample. Specifically, we evaluate whether one’s peers’ genetic propensity to smoke affects one’s own smoking behavior net of one’s own genotype. Results show that peer genetic propensity to smoke has a substantial effect on an individual’s smoking outcome. This is true not only when the peer group includes direct friends, and therefore where the individual plays an active role in shaping the metagenomic context but also when the peer group includes all grade-mates and thus in cases where the individual does not select the metagenomic environment. We explore these effects further and show that a small minority with high genetic risk to smoke (‘bad apples’) can greatly affect the smoking behavior of an entire grade. The methodology used in this paper offers a potential solution to many of the challenges inherent in estimating peer effects in nonexperimental settings and can be utilized to study a wide range of outcomes with a genetic basis. On a policy level, our results suggest that efforts to reduce adolescent smoking should take into account metagenomic effects, especially bad apples, within social networks.




adolescent smoking

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Journal Article

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Proceedings of the National Academy of Sciences


Sotoudeh, Ramina
Harris, Kathleen Mullan
Conley, Dalton

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