Modern acceptance of Haeckel's Biogenetic Law, despite current rejection of Haeckelian views, finds support in the certain degree of parallelism between ontogeny and phylogeny. A. M. Khazen, on the one hand, states that "ontogeny is obliged to repeat the main stages of phylogeny." A. S. Rautian, on the other hand, argues that the reproduction of ancestral patterns of development is a key aspect of certain biological systems. Dr. Rolf Siewing acknowledges the similarity of embryos in different species, along with the laws of von Baer, but does not believe that one should compare embryos with adult stages of development. According to M. S. Fischer, reconsideration of the Biogenetic Law is possible as a result of two fundamental innovations in biology since Haeckel's time: cladistics and developmental genetics.