In lieu of an abstract, here is a brief excerpt of the content:

IA BIg PICTuRE of BIg PICTuRES of LIfE’S HISToRy Brett Calcott and Kim Sterelny In the introduction, we suggested that the single most important feature of Maynard Smith and Szathmáry’s Major Transitions was its dynamic approach: The major changes are those that affect the key elements in the process of evolution itself. Even if this is right, it still does not isolate a single line of investigation about major transitions, nor a single way of understanding how and why they might occur. The chapters in this section sample a number of approaches to the major transitions. Each chapter critiques or extends the major transitions framework in some way, but not in the same way, nor with the same goal. Okasha , for example, takes the existing framework for granted, and argue that it entails a conceptual shift in the way we think of organisms. McShea and Simpson, in contrast, are skeptical that there is unity within the major transitions as they are currently laid out. Some of these different approaches reflect ambiguities within the major transitions literature itself (McShea and Simpson do a particularly good job of identifying some of these problems ). But the different approaches also reveal the fertile ground that exists for integrating, assessing, and applying work done on the major transitions with other ideas, both in biology (such as evolvability) and in philosophy of science (such as unification, and the nature of explanation). McShea and Simpson argue that Maynard Smith and Szathmáry do not provide a coherent , well-motivated framework for thinking about the history of life. Their specific transitions do not cohere with their advertised framework, nor can the framework be modified in a principled way to fit their list of canonical major transitions. The chief problem they see is that the final transition to human societies is an outlier; whatever it is that unifies the other transitions, it is simply not the same thing going on in this final, human, case. McShea and Simpson survey a number of earlier, lesser known, attempts to find some property that underlies and unifies large-scale evolutionary change, contrasting Maynard Smith and Szathm áry’s Major Transitions with Julian Huxley’s investigation of higher and lower organisms and Stebbin’s eight levels of organization. Each of these various frameworks is found wanting. McShea and Simpson don’t simply dismiss such frameworks because they might be thinly disguised versions of a “great chain of being,” which places humans at the topmost rung. They take seriously the idea that, in principle, there could be some property that 16 Part I does increase over time, and is maximized in some way with humans. In their assessment, however, none of these frameworks captures a consistent, measurable property that justifies such an ordering. They conclude by suggesting we treat more seriously the demand for theoretical consistency in any such broad-sweeping framework. Calcott argues that the major transitions literature has been too focused on identifying conditions in which there is selection for cooperation, despite the threat of defection. While this is undoubtedly important, Calcott proposes that there are alternative resources we can draw upon to help understand these transitions. Mayr, Tinbergen, and others have remarked that there are different kinds of explanation in biology, and Calcott suggests that these other kinds of explanation reveal different ways of identifying theoretical unity across major transitions (Mayr 1961; Tinbergen 1963). Using examples from the evolution of multicellularity in Volvox carteri, a green algae, he shows how different researchers have deployed very different kinds of explanation to pick out different factors important in enabling this particular transition. This model system may exemplify the distinctive selective pressures necessary for a major transition, but it also exemplifies the engineering challenges involved in an expansion of vertical complexity. In this case, the factors that allow these challenges to be met are specific to V. carteri; however, they suggest more general conditions, involving similar structural and organizational challenges, that are present across the major transitions . Identifying these organizational prerequisites for a growth in complexity, and understanding how they might interact with the more familiar levels of selection problems, provides one way of extending work on major transitions. Okasha’s chapter explores the implications of a framework that acknowledges multiple levels of organization, arguing for a displacement of the organism as a privileged level of analysis in evolutionary biology. Much work in multilevel selection is still conceptually anchored to the organism, conceptualizing genetic and cellular evolution as evolution “below the...

Share