image: Mesic shrub tundra in Northwestern Alaska, similar to the environment humans occupied in Beringia during the Last Glacial Maximum. view more
Credit: PNAS
Researchers report evidence of selection on human mammary gland development at high latitudes. Evidence suggests that the ancestors of the first Native Americans lived in genetic isolation on the Arctic Beringian landmass during the Last Glacial Maximum, approximately 20,000-30,000 years ago. Little ultraviolet (UV) radiation, which is necessary for vitamin D biosynthesis, reaches the Earth's surface at such high latitudes, thereby increasing the risk of vitamin D deficiency. Leslea Hlusko and colleagues investigated the possibility of genetic adaptation to low UV exposure in this population. The ectodysplasin A receptor (EDAR) gene influences the development of ectodermally derived structures, including teeth and mammary and sweat glands. A variant of this gene, EDAR V370A, has a highly elevated frequency in North and East Asian populations and is associated with increased sweat gland density, branching of mammary gland ducts, and shovel-shaped incisors, among other effects. The authors found a high degree of incisor shoveling among archaeological Native American populations, suggesting that the variant was also frequent among Native Americans prior to European colonization, and therefore among their ancestral Arctic population. According to the authors, the high-latitude, low-UV environment of Beringia may have selected for this variant because of its effect on mammary ductal branching, which may amplify the transfer of vitamin D and other nutrients to offspring via breast milk.
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Article #17-11788: "Environmental selection during the last ice age on the mother-to-infant transmission of vitamin D and fatty acids through breast milk," by Leslea J. Hlusko et al.
MEDIA CONTACT: Leslea J. Hlusko, University of California, Berkeley, CA; tel: 510-643-8851; e-mail: <hlusko@berkeley.edu>
Journal
Proceedings of the National Academy of Sciences