Throughout the last quarter of the nineteenth century, researchers became increasingly interested in explaining the ways in which mammalian teeth, especially molars, and their complex arrangements of cusps arose along both developmental and evolutionary timescales. By the 1890s, two theories garnered special prominence; the tritubercular theory and the concrescence theory. The tritubercular theory was proposed by Edward Drinker Cope in 1883, and later expanded by Henry Fairfield Osborn in 1888, while the concrescence theory was developed by Carl Röse in 1892. (...) Reviews concerning the evolution of mammalian molar teeth tended to paint the two theories as occupying opposing sides, and debates arose between their main proponents; however, their tenets do not seem logically incompatible. Throughout this paper, I argue that the conflict that arose was due not to the content of the theories, but to a diverse array of commitments Cope, Osborn, and Röse held, which turned into background assumptions within the setting of these theories. This history traces the context in which Cope, Osborn, and Röse developed the tritubercular and concrescence theories, and the ways in which the assumptions that these investigators held influenced their perceptions of their theories. (shrink)

Stem cells did not become a proper research object until the 1960 s. Yet the term and the basic mind-set—namely the conception of single undifferentiated cells, be they embryonic or adult, as the basic units responsible for a directed process of development, differentiation and increasing specialisation—were already in place at the end of the nineteenth century and then transmitted on a non-linear path in the form of tropes and diagrams. Ernst Haeckel and August Weismann played a special role in this (...) story. The first coined the term Stammzelle (stem cell), the second was the author of the first cellular stem-tree diagram. Even today, I shall argue, the understanding of stem cells, especially the popular perception, is to a large extent a Haeckelian–Weismannian one. After having demonstrated this, by analysing the terminology, in this essay I will focus on the use of cytogenetic tree diagrams between 1892 and 1925 and on the tacit understanding of stem cells that they transmit. (shrink)