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This chapter surveys the philosophical problems raised by two Darwinian claims: the existence of a "tree of life" and the explanatory power of natural selection. The first part explores philosophical issues concerning the process of evolution by natural selection. After laying out the nature of selectionist explanations, their conditions, and some of their correlated properties such as fitness, we present the epistemic issues raised by such explanations. These include the role of optimality considerations and dynamical modeling, as well as the respective contributions of analytical explanation and historical narratives to evolutionary understanding. Then the metaphysical aspects of natural selection are examined: whether it is a law or supports natural laws; whether it is a cause, and if so, the cause of what. The consequences of the answers to these questions for scientific practice, and especially for current controversies about a possible extension or revision of the Modern Synthesis, are highlighted. The chapter then presents two classical controversies regarding the target and the limits of selective explanations – units of selection, adaptationism – in both cases pointing out the promises of explanatory pluralism. The third section considers issues raised by evolutionary patterns: first, the interpretation of the nodes in the tree of life, where the notion of species is controversial; then, the question of the relationship between macro- and microevolution, and, relatedly, the connection between putative processes and plausible patterns. Consequences for the current controversy about the fate of the Modern Synthesis are also explained. We further explicate issues raised by general features of large-scale phylogenetic patterns, such as increases in complexity, and the question of evolutionary contingency, and discuss the chances of an empirical solution to these longstanding puzzles. The last section considers some consequences of evolutionary theory for philosophical questions about human nature, given the rise of hypotheses on the universality of selectionist explanations; it is mostly concerned with epistemology and psychology.

DOI: 10.1007/978-3-642-39979-4_2

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