  Within the context of PVA, Shaffer's classification—though usually with “random catastrophe” replacing “natural catastrophe”—became canonical within both ecology and conservation  biology.[25]  However, the philosophical question remains as to whether it makes sense—classification, as many philosophers have pointed out, is not innocent of substantive theoretical assumptions. The first point to note is that genetic stochasticity is not even the same type of mechanism as the other three: its presence makes Shaffer's classification oddly heterogeneous. The reason for this is that genetic stochasticity is a consequence of demographic stochasticity: in small populations, a particular allele may reach fixation purely by chance reproductive events. It is even possible that stochasticity increases the rate at which a beneficial allele may go to fixation in a small population provided that the initial frequency of that allele is already high.