A recurrent theme in the philosophical interpretation of biology has been the claim that the biological sciences are distinguished in some radical way from the physical sciences, and in particular from physics and chemistry. It used to be said by adherents of this view that the difference lay in the fact that the subject-matter of the life sciences was of a fundamentally different sort (e.g., a distinct kind of substance or force) from that dealt with by the physical sciences. And this difference was alleged to be radical in the sense that the sorts of substances or forces which are the special concern of biology operate according to laws (if indeed they operate according to any laws at all) which are different from and irreducible to those governing mere physical or chemical bodies. In more recent times, however, such positions have tended to be abandoned in favor of ones that located the distinction in some fundamental methodological or epistemological difference. Some have maintained, for example, that the distinctness of biology from physics (and chemistry) lies in the different mode or modes of explanation employed by the former, as opposed or in addition to those employed by the latter. This type of view of the difference, like the earlier type, is claimed by many of its adherents to imply the "irreducibility" of biology to physics.
Views of the latter sort have had many advocates and have taken many specific forms. One version has been presented by Professor G. G. Simpson in his fascinating book, This View of Life. According to Simpson, the differences between the physical and the biological sciences can be expressed in terms of kinds of scientific explanations and kinds of questions that elicit them. "How?" is the typical question in the physical sciences. There it is often the only meaningful or allowable one. It must also be asked in biology, and the answers can often be put in terms of the physical sci-