Division of Medical Genetics, Department of Political Science, University of California at San Diego, La Jolla, CA 92093, USA.
Proc Natl Acad Sci U S A. 2011 Feb 1;108(5):1993-7. doi: 10.1073/pnas.1011687108. Epub 2011 Jan 18.
It is well known that humans tend to associate with other humans who have similar characteristics, but it is unclear whether this tendency has consequences for the distribution of genotypes in a population. Although geneticists have shown that populations tend to stratify genetically, this process results from geographic sorting or assortative mating, and it is unknown whether genotypes may be correlated as a consequence of nonreproductive associations or other processes. Here, we study six available genotypes from the National Longitudinal Study of Adolescent Health to test for genetic similarity between friends. Maps of the friendship networks show clustering of genotypes and, after we apply strict controls for population stratification, the results show that one genotype is positively correlated (homophily) and one genotype is negatively correlated (heterophily). A replication study in an independent sample from the Framingham Heart Study verifies that DRD2 exhibits significant homophily and that CYP2A6 exhibits significant heterophily. These unique results show that homophily and heterophily obtain on a genetic (indeed, an allelic) level, which has implications for the study of population genetics and social behavior. In particular, the results suggest that association tests should include friends' genes and that theories of evolution should take into account the fact that humans might, in some sense, be metagenomic with respect to the humans around them.
众所周知，人类倾向于与具有相似特征的其他人交往，但这种倾向是否会对人群中的基因型分布产生影响还不清楚。尽管遗传学家已经表明，人群往往会在遗传上分层，但这一过程是由于地理上的分类或选择性交配造成的，而且还不清楚基因型是否可能由于非生殖性的关联或其他过程而相关。在这里，我们研究了来自国家青少年健康纵向研究的六个可用基因型，以测试朋友之间的基因相似性。友谊网络的图谱显示出基因型的聚类，并且在我们对人口分层进行严格控制之后，结果表明一种基因型呈正相关（同质性），而一种基因型呈负相关（异质性）。在弗雷明汉心脏研究中的一个独立样本的复制研究验证了 DRD2 表现出显著的同质性，而 CYP2A6 表现出显著的异质性。这些独特的结果表明，同质性和异质性在遗传（实际上是等位基因）水平上获得，这对群体遗传学和社会行为的研究具有重要意义。特别是，这些结果表明，关联测试应该包括朋友的基因，而进化理论应该考虑到人类在某种意义上可能与周围的人类具有共生关系的事实。
