Rachael Louise Brown

Evolutionarily minded psychologists and philosophers routinely invoke gradualism when theorising about human cognition, assuming human cognitive evolution evolved via a series of gradual phenotypic steps from an ancestral trait to the trait of interest. I argue this assumption is neither theoretically required nor empirically well supported. Evolutionary biology provides clear cases where major phenotypic shifts occur rapidly, and there is no principled reason to exempt cognition from this pattern. Acknowledging this leads to a more nuanced view of what makes explanations of human psychology evolutionarily plausible, and of what a successful evolutionary approach to psychology should aim to provide.

Birch’s formulation is persuasive but not nuanced enough to capture at least one situation where it is reasonable to invoke the precautionary principle (PP): when we have multiple, weak, but convergent, lines of evidence that a species is sentient, but no statistically significant evidence of a single credible indicator of sentience within the order as required by BAR. I respond to the worry that if we include such cases in our framework for applying the PP, we open ourselves to the charge of being “unscientific.”

Made famous by Ernst Mayr (1961), the distinction between proximate and ultimate causation in biological explanation is widely seen as a key tenet of evolutionary theory and a central organizing principle for evolutionary research. The study of immediate, individual-level mechanistic causes of development or physiology (“proximate causation”) is distinguished from the study of historical, population-level statistical causes in evolutionary biology (“ultimate causation”). Since evolutionary developmental biology (evo-devo) is a field that explicitly uses so-called “proximate” sciences such as developmental biology, morphology, and embryology in the study of evolution, it challenges the standard construal of the proximate-ultimate distinction and its associated account of causation. The exact nature of the challenge and its ramifications for the viability of the distinction more broadly are contested, but these conceptual questions are central to the status and significance of evo-devo in contemporary evolutionary biology.

Historically, the empirical study of phenotypic diversification has fallen into two rough camps; (1) "structuralist approaches" focusing on developmental constraint, bias, and innovation (with evo-devo at the core); and (2) "adaptationist approaches" focusing on adaptation, and natural selection. Whilst debates, such as that surrounding the proposed "Extended" Evolutionary Synthesis, often juxtapose these two positions, this review focuses on the grey space in between. Specifically, here I present a novel analysis of structuralism which enables us to take a more nuanced look at the motivations behind the structuralist and adaptationist positions. This makes clear how the two approaches can conflict, and points of potential commensurability. The review clarifies (a) the value of the evo-devo approach to phenotypic diversity, but also (b) how it properly relates to other predominant approaches to the same issues in evolutionary biology more broadly.

In recent years, the concept of evolvability has been gaining in prominence both within evolutionary developmental biology (evo-devo) and the broader field of evolutionary biology. Despite this, there remains considerable disagreement about what evolvability is. This article offers a solution to this problem. I argue that, in focusing too closely on the role played by evolvability as an explanandum in evo-devo, existing philosophical attempts to clarify the evolvability concept have been overly narrow. Within evolutionary biology more broadly, evolvability offers a robust explanation for the evolutionary trajectories of populations. Evolvability is an abstract, robust, dispositional property of populations, which captures the joint causal influence of their internal features on the outcomes of evolution (as opposed to the causal influence of selection, which is often characterized as external). When considering the nature of the physical basis of this disposition, it becomes clear that the many existing definitions of evolvability at play within evo-devo should be understood as capturing only aspects of a much broader phenomenon. 1 Introduction2 The Problem of Evolvability3 The Theoretical Role of Evolvability in Evolutionary Biology3.1 The explanatory targets of evolutionary biology3.2 Selection-based explanations3.3 Lineage explanations3.4 Evolvability-based explanations3.5 What properties must evolvability have?4 What Evolvability Really Is4.1 Making sense of ft4.2 Making sense of x and b5 What of the Limbs? The Power of E6 Conclusion.