We are thus able to see more clearly how it is that the theory of evolution may be thought to give rise to two different ethical ends. The first of these is the theory already criticised, "adaptation to environment," which corresponds to the notion of self-preservation. But this end, as we have seen, only takes one side of the theory of evolution into consideration--neglects the tendency to variation which evolution postulates, and which, in the higher organisms, becomes purposed. The other end which seems to be suggested by the theory of evolution takes account of this tendency to variation, and may be said to correspond to the notion of self-development; but this end it is harder to define. Adaptation we can easily understand by a reference to the environment to which life is to be adapted. This involves a knowledge of the conditions of the environment, but nothing more. Development can be measured by no such standard. On the one hand it implies an independent, or relatively independent, tendency to variation. On the other hand, however, it is necessary that the disharmony with environment, in which this tendency to variation may begin, should not be excessive and should not be permanent; for without a certain amount of adaptation to environment no organism can live. The extent of initial disharmony which is possible, or is useful, varies according to the versatility of the faculties of each individual organism, and to its place in the scale of being; but throughout all existence it is true that want of adaptation beyond a certain varying degree is fatal: "a mode of action entirely alien to the prevailing modes of action, cannot be successfully persisted in--must eventuate in death of self, or posterity, or both."[230] [Sidenote: (_b_) Standard for measuring development]