Under the name of “Progenesis” (from the prefix “pro “, in front, and of the Greek “genesis “, generation) a new conception and classification of the factors of development were proposed by R. Turpin, the progenesis grouping “the whole of the hereditary and non hereditary factors that preexist to the fecundation and that concur to the formation of the being and to its development”.

This conception has the advantage of designating indifferently, to all progenitic factor, hereditary as well as non hereditary, a place marked in advance; it has the advantage of showing beside the paternal maternal factors, the characteristic progenetical factors of the couple; it has the advantage to draw the attention on factors which were before neglected (age of mother, age of father, rank of birth, sex of the preceding pregnancy, interval between pregnancies, number of pregnancies, etc.) and whose importance increases in proportion as the gathering of the facts is abundant enough to lend itself to the statistical analyses; it has lastly the advantage of leading to an etiological prevention of the congenital defects, trying to draw the most advantage from the surrounding factors, without discarding, when they are imposed by the circumstances, the possibilities brought to their right proportion of the eugenic selection.

To illustrate this progenesic conception of the ontogenesis a simple example, the gemellity, deserves to be retained.

If we consider the gemellity as a deviation in regard to the simple pregnancies, it constitutes at the same time the more frequent and the best registered of anomalies. It lends itself to the study of its relations with divers progenesic factors which the authors regard by turns with the complement of their personal researches : age of the progenitors, rank of the pregnancy, sex of the product of the anterior last conception.

If on the other hand, we consider the gemellity itself as a progenesic factor, we can study on the development, and for instance, which the authors have done, on the rate of masculinity. This study has lead them to put in value the phenomenon of diminution of the masculinity in relation to the degree of the multiplicity of pregnancy.