In the immediate aftermath of Darwin's work, the idea that the theory of evolution had ethical consequences became quite widespread. Perhaps what makes this idea appealing is the popular notion that the theory of evolution in some way displaces or supplants religion. Religion is, after all, often seen as the source of moral teachings. If the theory of evolution significantly weakens the case for religious beliefs then, it might be thought, it had better generate moral teachings of its own. The alternative might be to be left with no moral teachings at all. However, there are a great many philosophers who think that ethics does not in any way depend on religion for its justification. Many of the early attempts to derive ethical consequences from evolution seem, from today's perspective, misguided. But the idea that we can learn something about ethics from evolution has not gone away.

Fitness as a normative concept

Evolution provides an account of how it is that living things have parts that are purposeful, that are for something. A world of purely physical entities, devoid of life, would presumably also be a world devoid of purposes. Those who are committed to a purely physicalist view of the world, then, are seemingly also committed to the view that purposes came into the world by means of evolution. Evolution explains why hearts, eyes and so on are for something.