E. E. Just's broad, yet hidden, influence on modern cell and developmental biology

This year, 2019, marks the centennial of embryologist E. E. Just's discovery of what is known as the fast block to polyspermy. Just's observation of the subtle changes that occur at the egg's surface during fertilization (and in experimental parthenogenesis) led him to postulate that the egg, and indeed every cell, possesses a property he called independent irritability, which represents the cell's ability to respond in a physiologically-relevant way to a variety of signals or triggers. In this paper, I argue that Just's concept of independent irritability informed his contemporary Johannes Holtfreter as Holtfreter attempted to explain the phenomena of embryonic induction and competence and that Holtfreter, in turn, influenced Marc Kirschner and John Gerhart in their formulation of the theory of facilitated variation. Just's influence is especially evident in Gerhart and Kirschner's presentations of what they call weak linkage-a property of living systems that allows core processes and components to be mixed and matched in different ways to generate novel traits. Unfortunately, the connection between Holtfreter's work and Just's has remained hidden. This paper gives examples of phenomena that exhibit weak linkage, and it lays out the case that Just's concept of independent irritability, through Holtfreter, Gerhart, and Kirschner, has broadly infiltrated modern cell and developmental biology.