0 0.2 0.4 0.6 0.8 r$_{31}$ 0.005 0.01 0.015 0.02 P[N>0] Model C FIG. 7: Simulation results for model C with r$_{12}$ = 0 . 51. Black circles correspond to r$_{13}$ = 0 . 45 and red squares to r$_{13}$ = 0 . 25. Other parameter values: µ = 0 . 001, ϵ = 10 − $^{5}$, and α = 1. removed we calculate the probability that the population survives both with and without quiescence. This scenario is highly relevant to evolutionary escape from drugs which have a finite life-span. This particular escape problem was considered Iwasa et al.[1]. The corresponding results are shown in Figs. 5 and 6. Fig. 6 shows the survival probabil- ity, P [ N > 0], as a function of r$_{13}$ and, indeed, we observe that when quiescent individuals are not considered, i.e. r$_{13}$ = 0, the probability of surviving after the end of the activity period of the hostile agent is null. As r$_{13}$ increases, so does the corresponding survival prob- ability, thus further confirming that quiescence is a feasible mechanism to help biological populations to escape harsh environmental conditions. Moreover, Fig. 5, which show par- ticular realisations of the process with (panel (b)), and without (panel (a)), quiescence also helps to understand more about the mechanism whereby quiescence allows escape: as can be seen in Fig. 5, panel (b), during the period of activity of the hostile agent most of the population is actually quiescent with a little proportion of the population in types (1) and (2). This means that quiescence mediates survival by acting as a reservoir or buffer. An alternative model. Whilst the results discussed until here provide compelling evidence in favour of hypothesis that the presence of quiescence can induce escape without the need of an increase in the reproductive fitness of any particular type of organism, some doubt could be cast on our argument so far. One might feel inclined to argue that our model still relays on a multi-type population where one type (type 1) is effectively more fit than the others. To adress this possibility, we consider model C in diagram 1. This version is closely related to the current discussion concerning the response of cancer cells to oxygen starvation. This model is also formulated in terms of a GWMBP and characterised in terms 9