Figure 2

General outline of the approach. What we are aiming for with our analysis is an explicit description of how the fate of individual cell lineages (their stemness) is related to the fate of the tissue. By a "cross-level principle" we refer to a rule by which the stemness of lineages constituting a tissue can be related to the fate of that tissue. The stemness is assessed in terms of the capacity of the cell lineages to contribute towards a tissue fate. The mathematical implementation uses order relations. A specific instance of a cross-level principle will be encoded formally by a function, called "lineage-tissue mapping". xP _i y denotes that x is more feasible than y, that is, the propensity of x is greater than that of y. The subscript i refers to a particular lineage, while P without the subscript refers to the tissue.