Rethinking the role of chance in the explanation of cell differentiation

How does it happen that populations of clonal cells show cell-to-cell variability even when their environment is kept homogeneous and constant? Until the mid-twenty century, isogenic populations of cells were treated as ideal gases, so that phenotypic variability among genetically identical cells that are placed in the same environment was being faded away. Today, cell-to-cell nongenetic variability has been acknowledged and shown to be due to stochastic fluctuations during the process of gene expression, what has started to be called “noise.” Such variability is thus considered simply as an error, a random deviation with respect to what is expected when one knows their genotype and the environment they grow in. In this context, chance is not considered as an explanatory element of the developmental process. Despite this predominant viewpoint, there is now more and more evidence that stochasticity can also play a role in the development of biological systems, sometimes even a functional one, rather than always being a mere nuisance. This opens the possibility for it to enter into biological explanations alongside acknowledged deterministic processes. In this chapter, we take these recent research results seriously. In their light, we argue that stochasticity affecting various biological processes involved in cell functioning and organism development can actually play a positive, constructive role, and should thus be conceived as more than just noise. We thus argue for a positive conception of chance, which is intended to enrich and augment the current, mostly negative, epistemology of chance that characterizes the biological discourse since the 1970s. More explicitly, we argue that chance can enter in descriptions and explanations of cellular and developmental processes as a specific biological parameter which, with other factors, characterizes and accounts for the behavior of biological systems.