 A different strategy is integrative pluralism (Mitchell 2002). This involves a two-step procedure for explaining complex phenomena whose features are the result of multiple causes: (a) formulate idealized models where particular causal factors operate in isolation (“theoretical modeling”); and, (b) integrate idealized models to explain how particular, concrete phenomena originate from these causes in combination. This model is suggestive but also has key drawbacks that include the fact that genetic causal reasoning in developmental biology does not typically involve theoretical modeling and the precise nature of the integration is underspecified. Integration of genetic and physical difference makers in a single mechanism offers a further possibility (Darden 2006; Craver 2007). Although this valuably highlights the productive continuity between difference makers through stages in a sequence (i.e., their reciprocal interplay), it also has handicaps. These include: