ABSTRACT
L ife on our planet has undergone tremendous and dramatic changes since its beginning, both in the natural world into which we are born and the social world we have created and in which we live. What do we mean by the natural and the social worlds? Clearly, at birth all living things enter a physical world that is not of their own making. Plants and animals either adapt to this ready-made environment or die out. They cannot change the nature of their habitat, for on planet Earth all living organisms exist in an environment shaped by forces and governed by laws that are only partially and imperfectly understood and only minimally amenable to change or control. Early humans did not understand this world, so they attributed many phenomena to spirits and supernatural beings. Today, the natural world is studied by the methods of science in such disciplines as biology, physics, chemistry, ecology, and so on. These disciplines are the so-called natural or exact sciences and are not within the realm of our inquiry in this text.
