a biological theory according to which the sexual cells of organisms contain material structures that predetermine the development of the embryo and the character of the organism.

The processes of fertilization and cell division (mitosis), as well as the mechanics of development (ontogeny), were clarified in the second half of the 19th century. As a result, other theories of development were found untenable: (1) epigenesis, the theory that the complete neoformation of the parts of the body occurs in structureless sexual cells; (2) ectogenesis, the theory that development depends on external conditions alone; and (3) vitalism, the theory that development depends on nonmaterial goal-related factors.

Studies at the end of the 19th century of the individuality of the chromosomes enclosed in cell nuclei and of their role in processes of fertilization and heredity gave rise to many hypothetical theories on heredity and development that were to one degree or another preformist. At the beginning of the 20th century, with the emergence of the science of genetics, these hypotheses were scientifically substantiated. It was shown that the sexual cells, or gametes, contain material structures, or genes, that are transmitted from generation to generation and determine the traits of the developing organisms. The centuries-old, often contradictory preformist biological concepts became conclusive in the 1950’s, with the discovery of the chemical nature of genes and the mechanisms for storing and transmitting genetic information, which determines the development of every species and individual. Modern preformism, therefore, should not be confused with the first naive ideas on the existence of completely formed embryos in the sexual cells, or preformation.

An authentic materialist theory of organic development should be a dialectical synthesis of preformed structures and the epigenetic factors of development.