Ectoderm-mesoderm interactions are essential for the proper formation of several structures that arise from the ectoderm, including the skin, hair, nails, teeth, and sweat glands.
[14][15] It has been hypothesized that natural selection favored this allele during the last ice age in a population of people living in isolation in Beringia, as it may play a role in the synthesis of Vitamin D-rich breast milk in dark environments.
[16][17][18] One study suggested that because the EDAR mutation arose in a cool and dry environment, it may have been adaptive by increasing skin lubrication, thus reducing dryness in exposed facial structures.
[22] According to a 2018 study, several ancient DNA samples from the Americas, including USR1 from the Upward Sun River site, Anzick-1, and the 9,600 BP individual from Lapa do Santo, were found to not carry the derived allele.
[23] A 2021 study analyzed the DNA of 6 Jomon remains from Japan and found that none of them carried the derived EDAR allele that is fixed in modern East Asian populations.