  Embryogenesis, the process by which an organism forms and develops, has long
been and still is a major field of investigation in the natural sciences. By
which means, which forces, are embryonic cells and tissues assembled, deformed,
and eventually organized into an animal? Because embryogenesis deeply questions
our understanding of the mechanisms of life, it has motivated many scientific
theories and philosophies over the course of history. While genetics now seems
to have emerged as a natural background to study embryogenesis, it was intuited
long ago that it should also rely on mechanical forces and on the physical
properties of cells and tissues. In the early 20th century, Stephane Leduc
proposed that biology was merely a subset of fluid physics, and argued that
biology should focus on how forces act on living matter. Rejecting vitalism and
life-specific approaches, he designed naive experiments based on osmosis and
diffusion to mimic shapes and phenomena found in living systems, in order to
identify physical mechanisms that could support the development of the embryo.
While Leduc's ideas then had some impact in the field, notably on later
acclaimed D'Arcy Thompson, they fell into oblivion during the later 20th
century. In this article I give an overview of Stephane Leduc's physical
approach to life, and show that the paradigm that he introduced, although long
forsaken, becomes more and more topical today, as developmental biology
increasingly turns to physics and self-organization theories to study the
mechanisms of embryogenesis. His story, I suggest, bears witness to our
reluctance to abandon life-specific approaches in biology.
