Interpolated map of the percentage of adults that can digest lactose in the indigenous population of the Old World. Circles mark sample locations.
Own work (http://www.joeroe.eu/blog/lactose-intolerance-around-the-world/)

DataItan, Yuval (2010). "A worldwide correlation of lactase persistence phenotype and genotypes". BMC Evolutionary Biology 10: 36. DOI:10.1186/1471-2148-10-36. PMID 20144208. PMC: 2834688. ISSN 1471-2148.
Global Lactase persistance Association Database. Molecular and Cultural Evolution Lab. University College London (April 2012). Retrieved on 3 July 2017.
Joe Roe