Infants with body mass at birth deviating from the mean values exhibit higher level of mortality. The absence of the expressed phenotype deviations refers to the preservation and heredity of the most adopted genotypes (reference values). The newborns out of the adaptive norm are morbidity-prone. The reference value for body mass at birth was studied in the indegenous populations of the Kola Peninsula, Siberia, Far East and the Urals. By our data the Arctic Saami and the Far East Nanais show the reference values more distinct from other. Lasting (many-centuries-long) adaptation to specific environmental conditions leads to development of a special phenotype complex. The Saami and Nanais are the most representative populations of the arctic and the monsoon climate zones. Accordingly, the parameters of reference values of their newborns are significantly different from the characteristics of the infants of the moderate climate zone.