We analyse Microtus oeconomus material collected for 25 years (1982–1992, 1994–2005, 2009, 2010). Directional asymmetry (DA) was demonstrated for the teeth morphotypes, the adrenal and the kidney weights, and for the length of the hind paw as well.

Developmental approach to the study of the continuous traits DA formation reveals its dynamic character. DA may be formed both at the early and at the later development stages. But DA has a strong genetic determination and is not dependent on environmental factors and population density dynamics. Although each trait has its own dynamics DA in ontogeny, usually DA increases in the period of sexual maturation. Uncoordinated development of the sides in this period is seems associated with an increase in intensity of developmental processes. Our study argue that sexual dimorphism appears at the later developmental stages. Its manifestation is consistent with Geodakian’s evolutionary theory of sex.

Evolutionary significance of the DA is to increase both short-term individual fitness and long-term population adaptive capacity. Developmental approach to the study of morphological and functional asymmetries in animals opens new possibilities for the study of evolutionary processes.