 It was once thought that each science must have laws in order to offer explanations (see the entry on  scientific explanations),  but now this is seen as unnecessary (Giere 1999; Woodward 2003). The expectation that a science have a theory to accomplish the task of organizing and guiding inquiry is of similar vintage. It derives from an intuitive expectation of what counts as a mature science in the first place. Even if we find empirically successful and coherent traditions of research without a systematic theoretical framework providing guidance, then the science cannot be mature. One might shrug off these quasi-positivist appeals to maturity by invoking more flexible conceptions of theory and theory structure. But why retain the expectation that theories should accomplish the same epistemic tasks? It is a preconception about knowledge structure that is not plausible in light of the diversity of research practices found across the sciences. The few scientists who favor this philosophical response have different motivations. Instead of maturity, other reasons are salient, such as guidance in the face of a welter of biochemical detail or the need to forge a synthesis between evolution and  development.[5]