Here we have used two statistical tests of selection and uncovered evidence of positive selection at the nicotinic receptors on chromosome 8 chromosome 15. Multiple drug-related phenotypes are associated with SNPs in or near these loci, however for several reasons it is unlikely that these phenotypes are the direct targets of this selective pressure. We have proposed two possible explanations 1) phenotypes related to memory and learning and 2) phenotypes related to social behavior. We were only able to discover a modest association with memory-related phenotypes, likely due to the small sample size. We also are as of yet unable to test this second hypothesis because we do not have data in our sample for a phenotype measuring sociality. However this work is the first to explicitly describe signs of natural selection acting on loci underlying substance dependence phenotypes.
