 Yet even this is perhaps too strong, given that some parts of a mechanism might become unstable when removed from their mechanistic context. Later, Glennan (2002: S345) says that the properties of a part must be stable in the absence of interventions, or that parts must be stable enough to be called objects. This notion is perhaps too strong to accommodate the more ephemeral parts of some biochemical mechanisms or of the mechanisms of natural selection (Skipper and Millstein 2005; but see Illari and Williamson 2010).