TCF7L2 and type 2 diabetes mellitus: Previous studies provided genetic evidence for the role of the transcription factor 7-like 2 (TCF7L2) gene in the relationship between T2DM and adaptive evolution [226,227]; the researchers observed potential positive selection for HapA (a cluster of homogeneous haplotypes in TCF7L2), which was linked with T2DM, as well as several phenotypic traits related to energy metabolism among East Asian, European and West African populations [227].