The paper is an attempt at confrontation of categories of materialist dialectics, namely the law of dialectical contradiction and some biological conceptions of development of the living nature. As the living system is a hierarchically ordered system, the author draws his attention to the level of the population/kind and to the level of the ecosystem (biocenosis). On the level of the population/kind he concludes that Darwin’s principle of natural selection meets the criteria of common dialectical contradiction. In this case adaptively non-directed hereditary transformability and geometrical progression may be considered as the thesis and antithesis of dialectical contradiction. On the level of the ecosystem the author holds that if we intend to substantiate the progressive evolution we must 1. leave a narow kind-oriented standpoint of examination and pass to a hierarchically higherecosystemic level and 2. give up examination of evolutionary trends and concentrate on the interconnection of biological progress and regress.