Originally from the greek epi (on, upon, on top of) and genesis (origin); the theory that the embryo develops progressively by stages, forming structures that were not originally present in the ovum or the sperm. The concept has been extended to other areas of medicine, with somewhat different meanings. Some of the other meanings are 1) any change in an organism that is due to outside influences rather than to genetically determined ones; 2) the occurrence of secondary symptoms as a result of disease; 3) developmental factors, and specifically the gene–environment interactions, that contribute to development; 4) the appearance of new functions that are not predictable on the basis of knowledge of the part-processes that have been combined; and 5) the appearance of specific features at each stage of development, such as the different goals and risks that erik erikson (1902–1994) described for the eight psychosocial stages of human life (e.g., trust vs. Mistrust, autonomy vs. Doubt). The life cycle theory adheres to the epigenetic principle in that each stage of development is characterized by crises or challenges that must be satisfactorily resolved if development is to proceed normally.
The concept that the embryo develops anew from undifferentiated material in each generation. This is in contrast to preformation.
In embryology, the development of specific cells and tissues from undifferentiated cells of the early embryo.