Figure 4.

Evolutionary dynamics of OC, OB and MM cell types. Vertices mean that cell population is monotypic. Bone homoeostasis occurs in the absence of MM (OC–OB line), remaining stable in the presence of MM if β < 1 (a) and unstable otherwise (b,c). Whenever β < 1 but β + δ > 1 (b), a saddle point appears in the interior of the simplex, which maintains normal homoeostasis as a possible outcome of the coevolution of the three cells types. Unfortunately, most of the existing scenarios suggest that β > 1 is the rule, which means that the scenario depicted in panel (c) applies, even in the limit when δ = 0 (see main text for details).