3. The ethics of evolution--in whatever form we have as yet found it--has always proceeded on the assumption that life is desirable, and that it has a value which makes its pursuit and promotion a reasonable moral end. How this fundamental ethical assumption[248] is to be justified, I do not at present inquire. But the question must now be faced--What is meant by "life" when we say that its "increase" or "development" is the moral end, and speak of its "greatest totality" in a way that implies that it admits of quantitative measurement? The biological definition of life is itself matter of dispute. But, even were such a definition as that proposed by Mr Spencer agreed to, it would be insufficient to provide a standard for human conduct. The very generality which may make it fit to stand as a definition, or at least abstract description, of life, renders it at the same time incapable of serving as a criterion by which the various modes of the manifestation of life may be judged. One point, however, generally emphasised by the theory of evolution, may be admitted. The life which human conduct "ought" to increase is not merely that of one individual man, but the whole life of the community--"self, offspring, and fellow-men"--with which the individual life is bound up. Evolution has shown how the growth of the individual has been so dependent upon that of the whole body of society that it is impossible to separate their interests. At the same time, no complete identity has been brought about, and it remains one of the greatest difficulties of any empirical theory to harmonise their competing claims. For argument's sake, however, and to admit of the quality of the end being investigated apart from considerations as to the method of distribution, the question may be discussed as if natural selection had produced complete solidarity between the life of the individual and that of the race. What criterion have we, then, of the development of human nature or life? The answer at once suggests itself that the higher evolution of life can be accurately measured by the amount of pleasure got by living beings. But this view has been examined in the preceding chapter, and found to be unsupported by sufficient evidence; so that we are driven to seek for some non-hedonistic criterion that will give meaning to the phrase "development" or "increase of life," when prescribed as the ethical end. [Sidenote: Health as the end either used to interpret pleasure,]