Activation parameters of fibril formation of evolutionary differing collagens were investigated. It has been shown that in a heated solution formation of collagen fibrils of different origin proceeds in different temperature regions related with the environmental temperature of species range. Enthalpy and free energy of the activation of fibril formation were measured. The data obtained show that fibril formation is preceded by the conformation of the molecules. Biological significance of the correspondence between the temperature of denaturation and that of the species range is discussed. The above correspondence is the limiting expression of functional dependence of conformational flexibility on temperature. Directed selection realized in the course of evolution is required for maintaining the velocity of collagen synthesis at the constant level.