Paleolithic settlers from the last glacial maximum may be the source of the high frequency of D− allele in Europeans. (Top) European location of Paleolithic refuges at the time of the last glacial maximum. Note migration of population containing marker M173 (from Gibbons⁵⁸ ; reprinted with permission from American Association for the Advancement of Science). (Bottom) Distribution of the D− allele in Europe (from Mourant et al⁵² ; reprinted by permission of Oxford University Press).