Hylomorphism is the theory (originating with Aristotle (322 BC)) that all things are a combination of matter and form. Aristotle was one of the first ancient writers to approach the subject of life in a scientific way. Biology was one of his main interests, and there is extensive biological material in his extant writings. According to him, all things in the material universe have both matter and form. The form of a living thing is its soul (Greek 'psyche', Latin 'anima'). There are three kinds of souls: the 'vegetative soul' of plants, which causes them to grow and decay and nourish themselves, but does not cause motion and sensation; the 'animal soul' which causes animals to move and feel; and the rational soul which is the source of consciousness and reasoning which (Aristotle believed) is found only in man. Each higher soul has all the attributes of the lower one. Aristotle believed that while matter can exist without form, form cannot exist without matter, and therefore the soul cannot exist without the body.
Consistent with this account is a teleological explanation of life. A teleological explanation accounts for phenomena in terms of their purpose or goal-directedness. Thus, the whiteness of the polar bear's coat is explained by its purpose of camouflage. The direction of causality is the other way round from materialistic science, which explains the consequence in terms of a prior cause. Modern biologists now reject this functional view in terms of a material and causal one: biological features are to be explained not by looking forward to future optimal results, but by looking backwards to the past evolutionary history of a species, which led to the natural selection of the features in question.