[Sidenote: 1. Adaptation to environment: necessary for life;] 1. The first condition of development, and even of life, is correspondence between an organism and its environment. The waste implied in the processes which constitute the life of an organised body has to be supplied by nutriment got from surrounding objects. It requires food, air, light, and heat in due proportions in order that its various organs may do their work. When these circumstances change, either it adapts itself to the new conditions or death ensues. Thus "we find that every animal is limited to a certain range of climate; every plant to certain zones of latitude and elevation,"[192]--though nothing differs more among different species than the extent of an organism's adaptability to varying conditions. A definite organism and a medium suitable to it are called by Comte the two "fundamental correlative conditions of life"; according to Mr Spencer they constitute life. "Conformity" is absolutely necessary between "the vital functions of any organism and the conditions in which it is placed." In this conformity there are varying degrees, and "the completeness of the life will be proportionate to the completeness of the correspondence."[193] Even when life is not altogether extinguished, it is impeded by imperfect adaptation. Where external circumstances make the attainment of nourishment difficult and precarious, life is shortened in extent, and, within its limits, more occupied with simply maintaining its necessary functions--less full, varied, and active. The same holds good whether the external circumstances are natural or social,--applies equally to those whose energies are exhausted in the production of a bare livelihood from a niggard soil and unpropitious climate, and to those who, under changed conditions, feel the hardship of adapting themselves to a new social medium. [Sidenote: spoken of as the ethical end;] [Sidenote: defines the notion of self-preservation.]