 Since the 1970s, theorizing about macroevolution has focused on several important ideas: punctuated equilibria, species selection, hierarchical theory, historical contingency, passive vs. driven evolutionary trends, major evolutionary transitions, and more recently the zero-force evolutionary law (or ZFEL) defended by McShea and Brandon (2010). One philosophical challenge is to understand the relationships among these ideas; another is to work out what they might mean for the relationship between macro- and microevolution.