The Tajima’s D analysis and integrated haplotype score both indicate that the CHRNB3-A6 cluster is undergoing selection and in particular, the iHS scores suggest that it is the risk allele for nicotine dependence on chromosome 8 that is under positive selection. As it seems unlikely that risk for nicotine dependence is the phenotype undergoing selection, and because nicotinic receptors are involved in memory and learning, we hypothesized that a phenotype related to memory or learning, such as attention, might be the phenotype being selected.
