By now, however, we can see more clearly the way in which the various sciences with which we are concerned, of whose relations we had something to say at the beginning of this essay, properly interlock. They interlock thus. The physico-chemical sciences are basic to biology. Organisms are made of the same substances as are non-living compounds; their processes are therefore conformable to certain physico-chemical laws, such as the indestructibility of matter, the conservation of energy, and so forth; and in so far as we analyse the material aspect of life, physico-chemical concepts are _adequate_. On the other hand, physico-chemical concepts--or at least our present ones--are not _all-sufficient_. In the first place, the very complicated arrangement of matter which is found in living substance has not been yet sufficiently analysed by physics and chemistry: accordingly we find many processes occurring in biology--such as the directional changes in evolution of which we have spoken--which could not have been foretold on our present physico-chemical knowledge, but must be investigated separately as adding to our store of facts and principles, in the confident hope that a synthesis will one day be possible. Secondly, a whole new category of phenomena, the psychological, is first met with in biology, and to this we cannot as yet apply physical or chemical ideas at all. For a combination of these two reasons, biology deals with certain concepts which are not implicit in current physico-chemical ideas. Physics and chemistry are basic for biology, but they are not exhaustive. In a very similar way, biology is basic for sociology, but again not exhaustive. Certain limits are set to human life through man’s organic nature. Certain of his activities can be completely analysed in terms of biology. But other of his activities, especially those concerned with his new type of mental organization, find no counterpart in the rest of the biological kingdoms, and must be studied in and for themselves. Bergson would have us believe that evolution is creative. It is better to say, with Lloyd Morgan, that it is emergent. With new degrees of complexity, new qualitative differences emerge. Thus the sciences are a hierarchy, the subject-matter of one constituting the foundation for the next in the series. All that biology can do for sociology is to help her to build her foundations solidly and correctly: but we all know that without good foundations no building is safe. BIBLIOGRAPHY Bury, J. B., ’20. “The Idea of Progress.” London, 1920. Carr-Saunders, A. M., ’22. “The Population Problem.” Oxford, 1922. Hobhouse, L. T., ’01. “Mind in Evolution.” London, 1901. Huxley, J. S., ’12. “The Individual in the Animal Kingdom.” Cambridge, 1912. Keyser, ’21. “Science” (N.S.) New York, 1921. Kropotkin, Prince, ’08. “Mutual Aid, A Factor in Evolution.” London, 1908.