Cells, Development, and Evolution: Teeth Studies at the Intersection of Fields

Early in the twentieth century, biology was seen as grounded in the dual foundations of cells and evolution. Cells provided the most basic living unit, and evolution provided a way for cells to become established in different organisms. However, as the twentieth century progressed, cells and cellular level phenomena became embedded in different research traditions within developmental biology with varying connections to an evolutionary framework. While researchers focusing on differentiation could continue to link their research to evolution through heredity, those focused on morphogenesis largely gave up any evolutionary perspective. Morphogenetic research programs continued, without evolution, until late into the twentieth century, when fruitful new insights brought development back into the process of evolution. This chapter takes teeth as an exemplary case study for these changes with special focus on the enamel knot, now thought of as the morphogenetic control center of the developing tooth. Once development, and especially cellular level phenomena, was seen in the light of evolution, the enamel knot became the central component of a new paradigm in evolutionary developmental biology—one that, to this day, continues to provide a means of understanding the development and evolution of teeth. The intersection of cells and “the Darwinian tradition” is a complex relationship. This chapter offers an alternative history of the ways in which development, evolution, and cells were brought together throughout the twentieth century and challenges the common conception that genes are the sole locus of explanation for research at the intersection of development and evolution.