Alison K. McConwell

‘Gouldian arguments’ appeal to the contingency of a scientific domain to establish that domain’s autonomy from some body of theory. For instance, pointing to evolutionary contingency, Stephen Jay Gould suggested that natural selection alone is insufficient to explain life on the macroevolutionary scale. In analysing contingency, philosophers have provided source-independent accounts, understanding how events and processes structure history without attending to the nature of those events and processes. But Gouldian Arguments require source-dependent notions of contingency. An account of contingency is source-dependent when it is indexed to some pattern and some process. Positions like Gould’s do not turn on the mere fact of life’s contingency—that life’s shape could have been different due to its sensitivity to initial conditions, path-dependence or stochasticity. Rather, Gouldian arguments require that the contingency is due to particular kinds of processes: in this case, those which microevolutionary theory cannot account for. This source-dependent perspective clarifies both debates about the nature and importance of contingency, and empirical routes for testing Gould’s thesis.

What is the relationship between evolutionary contingency and diversity? The evolutionary contingency thesis emphasizes dependency relations and chance as the hallmarks of evolution. While contingency can be destructive of, for example, the fragile and complex dynamics in an ecosystem, I will mainly focus on the productive or causal aspect of contingency for a particular sort of diversity. There are many sorts of diversities: Gould is most famous for his diversity-to-decimation model, which includes disparate body plans distinguishing different phyla. However, structural diversity construed more broadly spans scales, such as organization in and among cells, structural arrangements and biomechanics on various scales, and even the profile of ancestor-descendent relationships or community structure of interactions within ecosystems. By focusing on stochastic processes in contingent evolution, I argue that contingency causes structural diversity. Specifically, I focus on the plurality of structural types of cells, genetic codes, and phyla diversity as case studies.

In this dissertation, I explore the reach of the Evolutionary Contingency Thesis—a view that emphasizes the role of dependency relations and chance in evolution. Contingency produces diverse biological entities, processes, and mechanisms. I analyze the implications of evolution’s contingency in three areas. First, I address the problem of evolutionary individuality, which concerns the nature of entities that selection acts on. If we accept Lewontin’s 1970 view that individuals are selected, then what exactly are these individuals? I argue that evolutionary contingency and its diversity of outcomes causes a plurality of individuality types. These types of individuals emerge, evolve, and disappear through evolution. Second, I defend a disunified model of major transitions in evolution. Major transitions mark pivotal turning points in life’s history, such as the transition from unicellularity to multicellularity. Philosophers and biologists aim to unify evolution’s transitions by establishing a property all major events share. I argue that evolutionary contingency’s emphasis on diversity supports a disunified model of transitions. That is, we should expect numerous kinds of major transitions given the diverse sets of outcomes caused by evolutionary contingency. Finally, I extend the contingency analysis to a topic in philosophy of medicine: The nature of cancer. It is common to view cancer as a by-product of our evolution as multicelled creatures. However, Lean and Plutynski argue that cancer is also a direct product of evolution by selection. In both cases, cancer is characterized in terms of how it functions as an object of selection. I argue that the diversity among cancers suggests philosophers should shift their focus to cancers’ structural differences rather than only their functional similarities.

George G. Simpson (1902–1984) and Stephen J. Gould (1941–2002) were both engaged with the normative – i.e., social, cultural, political, and even ethical – consequences of their evolutionary theorizing. However, there is a normative point of departure between Simpson and Gould’s work in that regard that has received little attention. Yet, their motivations converge into a larger program of resistance and social protection from misconstrued and illegitimate overreaches of the biological sciences leading up to and after the peak of the modern synthesis.