Darwin’s discovery of descent with modification was inaugurated by a shift in perspective that Ernst Mayr (1975) has dubbed “population thinking.” Darwin realized that the explanation of the fit and diversity of organic form should be approached as a question about the constitution of populations. Rather than ask how individual organisms come to acquire their remarkable features—their complexity, their functional integration, their exquisite adaptedness to their conditions of existence—we should ask how populations come to comprise such individuals.

Organisms are like nothing else in the natural world. They are agents. Methodological vitalism is a view according to which the difference that organisms make to the natural world cannot be captured wholly if we treat them as mere objects. Understanding agency calls for a different kind of theory, an agent theory.

Jacques Monod’s Chance and Necessity poses a paradox for modern biology: Organisms both must be and cannot be purposive systems. To resolve the paradox we must explain purpose by appeals to invariance or invariance by appeal to purpose. The methodology of modern science, however, allows no unreduced appeals to purpose. Monod traces the modern synthesis commitment to ineluctable chance back to its animadversion to teleology. He credits the pre- Socratic Atomist philosopher Democritus with holding that everything in the world is the fruit of chance and necessity. It is becoming increasingly obvious that their purposiveness is pivotal to the dynamics of evolution. This chapter outlines a ‘neo-Aristotelian’ alternative to the neo-Democritean commitments of modern synthesis biology, one that accords the purposiveness of organisms a central explanatory role in evolution.

Walsh, D. M. The central insight of Darwin's Origin of Species is that evolution is an ecological phenomenon, arising from the activities of organisms in the 'struggle for life'. By contrast, the Modern Synthesis theory of evolution, which rose to prominence in the...