Perhaps nothing will so much hasten the time when body and mind will both be adequately cared for, as a diffusion of the belief that the preservation of health is a duty. Few seem conscious that there is such a thing as physical morality. Men's habitual words and acts imply the idea that they are at liberty to treat their bodies as they please. Disorders entailed by disobedience to nature's dictates, they regard simply as grievances; not as the effects of a conduct more or less flagitious. Though the evil consequences inflicted on their dependents, and on future generations, are often as great as those caused by time, yet they do not think themselves in any degree criminal. It is true that, in the case of drunkenness, the viciousness of a bodily transgression is recognised; but none appear to infer that, if this bodily transgression is vicious, so, too, is every bodily transgression. The fact is, that all breaches of the laws of health are physical sins. When this is generally seen, then, and perhaps not till then, will the physical training of the young receive the attention which it deserves.
In 1860 Spencer commenced a connected series of philosophical works, designed to unfold in their natural order the principles of biology, psychology, sociology and morality. "Principles of Biology" was published in 1864, and aims to set forth, the general truths of biology as illustrative of, and as interpreted by the laws of evolution. It was revised in 1899.
Proximate Definition of Life
To those who accept the general doctrine of evolution, it needs scarcely to be pointed out that classifications are subjective conceptions which have no absolute demarcations in nature corresponding to them. Consequently in attempting to define anything complex we can scarcely ever avoid including more than was intended, or leaving out something that should be taken in. Thus it happens that on seeking a definition of life there is great difficulty in finding one that is neither more nor less than sufficient. As the best mode of determining the general characteristics of vitality, let us compare its two most unlike kinds and see in what they agree.
Choosing assimilation, then, for our example of bodily life, and reasoning for our example of the life known as intelligence, it is first to be observed that they are both processes of change. Without change food cannot be taken into the blood nor transformed into tissue: neither can conclusions be obtained from premises. This conspicuous manifestation of change forms the substratum of our idea of life in general. Comparison shows this change to differ from non-vital changes in being made up of successive changes. The food must undergo mastication, digestion, etc., while an argument necessitates a long chain of states of consciousness, each implying a change of the preceding state. Vital change is further made up of many simultaneous changes. Assimilation and argument both include many actions going on together. Vital changes, both visceral and cerebral, also differ from other changes in their heterogeneity; neither the simultaneous nor the serial acts of digestion or of ratiocination are at all alike. They are again distinguished by the combination subsisting among their constituent changes. The acts that make up digestion are mutually dependent; as are those which compose a train of reasoning. Once more, they differ in being characterised by definiteness. Assimilation, respiration, and circulation, are definitely interdependent. These characterisations not only mark off the vital from the non-vital, but also creatures of high vitality from those of low vitality. Hence our formula reads thus:—Life is the definite combination of heterogeneous changes, both simultaneous and successive. Not a definite combination, allowing that there may be others, but the definite combination. This, however, omits its most distinctive peculiarity.
Correspondence Between Life and Its Circumstances
We habitually distinguish between a live object and a dead one by observing whether a change in the surrounding conditions is or is not followed by some perceptible and appropriate change in the object. Adding this all-important characteristic, our conception of life becomes—the definite combination of heterogeneous changes, both simultaneous and successive, in correspondence with external coexistences and sequences. Some illustrations may serve to show the significance of this addition.