Sunshine and the geographical distribution of the alleles of the Gc system of plasma proteins.

Following the discovery by Daiger et al. (1975) that the Gc proteins of human plasma act as the carriers of vitamin D, the authors have plotted on a world map all available data on the frequency of the allele Gc2, and compared the distribution with that of sunlight. With some exceptions high frequencies of Gc2 correspond to low levels of sunlight and vice versa. Similar comparisons within Ireland show no such relation. The results are discussed in relation to natural selection and the incidence of rickets, due to vitamin D deficiency.