In 1956, in his Principles of Embryology, Conrad Hal Waddington explained that the word “epigenetics” should be used to translate and update Wilhelm Roux’ German notion of “Entwicklungsmechanik” to qualify the studies focusing on the mechanisms of development. When Waddington mentioned it in 1956, the notion of epigenetics was not yet popular, as it would become from the 1980s. However, Waddington referred first to the notion in the late 1930s. While his late allusion clearly reveals that Waddington readily associated the (...) notion of epigenetics with the developmental process, in the contemporary uses of the notion this developmental connotation seems to have disappeared. The advent and success of molecular biology have probably contributed to focusing biologists’ attention on the “genetic” or the “non-genetic” over the “developmental”. In the present paper, I first examine the links that exist, in Waddington’s work, between the classical notion of epigenesis in embryology and those of epigenetics that Waddington proposed to connect, and even synthesize, data both from embryology and genetics. Second, I show that Waddington’s own view of epigenetics has changed over time and I analyze how these changes appear through his many representations of the relationships between genetic signals and developmental processes. (shrink)

Morphogenesis is one of the fundamental processes of developing life. Gastrulation, especially, marks a period of major translocations and bustling rearrangements of cells that give rise to the three germ layers. It was also one of the earliest fields in biology where cell movement and behaviour in living specimens were investigated. This article examines scientific attempts to understand gastrulation from the point of view of cells in motion. It argues that the study of morphogenesis in the twentieth century faced a (...) major dilemma, both epistemological and pictorial: representing form and understanding movement are mutually exclusive, as are understanding form and representing movement. The article follows various ways of modelling, imaging, and simulating gastrular processes, from the early twentieth century to present-day systems biology. The first section examines the tactile modelling of shape changes, the second cell cinematography, mainly the pioneering work of the German embryologists Friedrich Kopsch and Ernst Ludwig Gräper in the 1920s but also a series of classic, yet not widely known, studies of the 1960s. The third section deals with the changes that computer simulation and live-cell imaging introduced to the modelling of shape change and the study of cell movement at the turn of the twenty-first century. Although live-cell imaging promises to experiment upon and represent the living body simultaneously, I argue that the new visuals are an obstacle rather than a solution to the puzzle of understanding cell motion. (shrink)