The general "plan" of animal structure evolves due to the changes both, in body proportions and body size. The method allowing to estimate the level of population differentiation according to these two parameters was considered. In the process of population differentiation two phases of form formation can be discerned. On the first stage of microevolution the morphogenesis mainly proceeds by ... [Show full abstract] proportion changes. The next stage is characterised primarily by changes of size. The same phase can be observed at intra-population level. The selection directed to the increase in differentiation of individuals according to their proportions.