A State of Uncertainty: Stemness and the Roles of Theory

Abstract

The stem cell uncertainty principle shows that evidential significance of stem cell experiments hinges on details of the method used (Chapter 3). Insofar as they are empirically-confirmed, hypotheses about single stem cells are relative to organismal source, characters measured, and manipulations performed within a temporal duration of interest. Evidence for population-level models also depends on such hypotheses. These evidential constraints create serious challenges for a research program aimed at prospectively identifying stem cells on the basis of ‘signature’ traits. To overcome these limitations, a number of stem cell researchers propose a conceptual revision: replace the notion of ‘the stem cell’ as cellular entity with that of a cell state, ‘stemness.’ The idea of a cell state is usefully contrasted with that of a cell type.⁶⁶ A cell type is defined by a set of character values, such that a cell is classified as a particular type in virtue of having all (or most) of those character values. Characters in the set vary, ranging from structural to functional, morphological to biochemical, features of the cell as a whole, the cell surface, molecules, and internal structures. All, however, are conceived as characters of the cell. In contrast, a state is a functional role taken by a cell, within some larger process.