  Shaffer went on to argue that all these factors increase in importance as the population size decreases—a claim that will be questioned below—and, therefore, that their effects are hard to distinguish. Finally, he defined a minimum viable population (MVP): “A minimum viable population for any given species in any given habitat is the smallest population having at least a 95% chance of remaining extant for 100 years despite the foreseeable effects of demographic, environmental, and genetic stochasticity, and natural  catastrophes.”[22]  Both numbers (95% and 100 years) are conventional, and to be determined by social choice, rather than by biological factors, a point that Shaffer explicitly recognized.