 An alternative to comparative process tracing that has been proposed is extrapolation by knowledge of causal capacities. If C has a causal capacity to bring about E, then C causes E in a somewhat stable or invariant manner. Specifically, C will then continue to contribute to the production of E even when disturbing factors are present (Cartwright 1989). To establish that C has the causal capacity to cause E therefore means to show that C’s causing E is independent of the background in which C and E occur to some extent. And therefore, if C causes E in a model species or population and C has the causal capacity to bring about E, then there is some reason to believe that C causes E also in the target species or population (for a defense, see Cartwright 2011).