(e.g., evolutionary pressures can rapidly increase frequencies of adaptive SNPs in gene-regulating regions). But some have mildly harmful effects, perhaps depending on environmental conditions (e.g., preserving fat during an ice age but leading to obesity in the fast food era). The CDCV-GWAS strategy assumed that many different common SNPs have small effects on each disease, and that some could be found by testing enough SNPs in enough people.
