The article examines one of the most interesting problems of theoretical biology, the origins of which are already found in the philosophy of antiquity (Anaximander, Aristotle), but which has not yet received a final solution. It is a question of the unity of the "structure plan" of living organisms belonging to different classes (e.g. birds and insects), as well as the ways of its "recording" and transmission between generations. The problem was particularly actively discussed in the 18th and 19th centuries by both biologists and philosophers. At the height of the debate, the naturalists were divided into two camps: the so-called "joffruists" (supporters of Geoffroy St. Iler) and the followers of Cuvier. Several hypotheses were put forward by both sides, not only inventive but also amusing. A parallel discussion among embryologists (on the same topic) led to the division of scientists into preformists and epigenetics. In morphology, the center of gravity of the problem was shifted towards the identification and description of forming mechanisms (A.G. Gurvich). But, as genetics develop and its influence increases, the opinion (completely unfounded) has been established that the solution to all problems lies in the genome, it is necessary only to decipher it. However, since the 1950s, the direction of "epigenetics" (Waddington) has been developing and asserting the existence of mechanisms of heredity not recorded in the genome but affecting morphogenesis. The analysis of concepts leads to the conclusion that researchers are often guided by ideological preferences rather than experience data.