 It is clear that these different kinds of “alternatives” to reductionism successfully capture a number of features left untreated or ignored by theory reduction. However, it is an open question whether they supplant discussions of reduction or bear some complex relation to them (Craver 2005). Reasons in favor of the latter position include the continued use of “reductionist” language (for and against) in biological research, as well as the fact that a near universal reason for rejecting reduction and choosing an alternative is the problematic nature of theory reduction, which only represents a small space of the philosophical possibilities. One interpretation of some alternatives to reduction is that they are responding to the complexity of reduction that has become more apparent over the past two decades (e.g., seeing explanations as inherently interlevel), and the fact that biologists’ use of the term “reductionism” refers to different specific commitments in different cases and research contexts. Thus, for example, mechanisms approaches are another way to treat the heterogeneity of explanation (including reductive and non-reductive aspects), which was largely ignored in the literature on theory reduction, which assumed that a few select examples from biological research were representative. This heterogeneity is a pervasive feature of the history of biology; philosophical alternatives to reduction are responding in part to long-standing controversies among life science investigators about the legitimacy of reductionist research strategies and modes of explanation (see  Section 2).  The compatibility or conflict among these various alternatives and different accounts of explanation in biology is still being probed (e.g., Bechtel 2006, 40–44), but the traditional philosophical project of articulating a single notion of reduction to capture most essential aspects of theory structure and explanation across biology is unlikely to succeed.