Kovalevskii's Law

a distinctive characteristic of the evolution of organisms discovered by the Russian scientist V. O. Kovalevskii. According to the law, relative expediency of the organisms’ structure, which developed in the course of adaptation to certain environmental conditions, is achieved in various ways. The ways connected with comparatively superficial, primarily quantitative, changes in the body result in what is known as inadaptive types (inadaptive reduction), while those connected with deep, radical changes in the structure of organs and in their interrelationships lead to the more perfected, adaptive types (adaptive reduction).

In Kovalevskii’s opinion, inadaptive types appeared first in the history of each group of organisms, but they were subsequently succeeded by adaptive ones. Kovalevskii’s law was established with particular reference to the reduction (decrease in number) of digits in ungulates, which helped them adapt to certain environmental conditions. The same feature was later observed in the development of various groups of animals and plants.