When we turn to man and note the way in which he overcomes the difficulties of his environment, we find them to be mainly of a different order. His instruments are not personal, in the sense of being a part of his organic structure. We may say they do not belong to him so much as they do to the race; while they are certainly transmitted from generation to generation irrespective of individuals. Instead of achieving conquest of his environment by developing an organic structure, man creates an inorganic tool. In a sense he subdues and moulds the environment to his needs, rather than modifies his structure in order to cope with the environment. Against extremes of temperature he fashions clothing and builds habitations. He discovers fire, probably the most important discovery ever made by mankind. He adds to his strength in defence and attack by inventing weapons. He guards himself from starvation by planting seeds, and so harnesses the productive forces of nature to his needs. He tames animals and so secures living engines of labour. Later, he compensates for his bodily weaknesses by inventing instruments which aid sight, hearing, etc. Inventions are multiplied, methods of locomotion and transportation are discovered, and the difficulties of space and time are steadily minimized. The net result of all this is that as a mere biologic phenomenon man's evolution is checked. The biologic modifications that still go on are of comparatively small importance, except, probably, in the case of evolution against disease. The developments that take place are mainly mental in form and are social in their incidence.