The word nature stems from the Latin natura, whose meaning ranges from "birth" to "the order of things." In English, nature comprises all plants, animals, and ecosystems, as well as the biological and nonbiological materials and processes of our planet. This range of meaning narrows if we consider the use of the word natural. Something is natural if it is not artificial, if it pertains to or comes from the natural world. When we speak of bears, mountains, or evolution and say, "they are natural," we mean they are neither human nor created by humans. Thus the concept of nature is often restricted to beings, things, or processes which are not human in origin.

Conceptual and empirical inquiries into nature loosely center on eight questions. The first question is a scientific one, which simply asks what constitutes nature: What are its essential properties and how shall we classify...