Biological analysis may enrich our understanding of morality, but it is also limited. Science is not able to discover ethical principles in nature. Nor to justify them. Nor to evaluate them, say, based on evolutionary history. Nor even to develop them based on some presumed universal or "objective" principle of "human nature." Many have tried. All have failed (Farber 1994, Bradie 1994). Rather, the achievable aim is to explain how organisms such as humans evolved moral capacities, to form moral concepts and to act on them in particular environments. That may also involve describing how, as organisms, they are able to do so (neurologically, cognitively, emotionally, socially). To describe morality as a practice is not to prescribe any particular moral rule. To explain the behavior is not to justify it. Facts and values (is and ought) are conceptually distinct. Charles Darwin, in his own presentation, notably limited the scope of his analysis to the "natural history" of ethics (1871, p.71). Still, knowing how and why (historically) we value things may fruitfully guide reflections on the process. Having introduced these caveats, then, let us consider what biologists have discovered about morality as an evolved form of behavior.