Mammalian embryology and organogenesis

Abstract

Historical intoduction: The origin of the human being is one of the major philosophical questions. One way of answering it is through an ontogenetic and evolutionary approach. Theories about the developmental origin in the mother’s womb were first documented by Greek scholars in the 5th century BC (Breidbach 2015). Being dependent on the success of reproduction, fertility has triggered human thinking for a much longer period of human evolution as is documented in the art of the Paleolithic, the Mesolithic, the Neolithic, and later phases of human cultural evolution (Fig. 1). Fertility was manifested by the representation of stout mother goddesses with a demonstrative focus on their hips and breasts (Fig. 1C) and by the presentation of erect penises in men (Fig. 1G). In some cases, the process of birth was depicted as a key event of life (Fig. 1D). Birth, pregnancy, and lactation of other vertebrate species were also of interest to ancient cultures, and were illustrated, particularly among species that played an important role in everyday life, such as prey and domesticated, mostly mammalian, animals (Fig. 1A, I). Fertility rites, including hierogamy (Fig. 1H) and sodomy (Fig. 1J), are thought to have played a major role in prehistoric cults and were meant to increase the number of offspring and to guarantee their health (Frazer 1922, Campbell 1960).
These attempts to understand and to influence our own development culminated in the artificial representation of homunculi in the Renaissance age, in which a human was “created” by alchemists in a jar. The mental construct of a test-tube baby (Fig. 1K) was a symbol for the development of the human mind itself, which alchemists tried to raise to a higher level of cognition (Gebelein 1996, Wiesing 2004). The historical representation of homunculi also corresponds to the ideas of preformationists in the 17th century that the human being is fully present as a miniature in the male’s sperms and only has to unfold to progress through embryological development to a fully formed human (Fig. 1F; Hartsoeker 1694)