Ethics properly involves a consideration of the conduct of animals as well as of human beings, for the primary subject-matter of Ethics is conduct considered as producing good and bad results to self or others, or both, not, as most people believe, conduct as calling forth approbation or disapprobation. And even on this latter view, Ethics includes Animal Ethics, since we feel approbation or disapprobation with regard to many actions of animals. Animal Ethics includes, as its two cardinal principles, the opposed classes of altruistic and egoistic acts. For preservation of the species, benefits received must be, during immaturity, inversely proportionate to merit or capacities possessed, merit being measured by powers of self-sustentation, and after maturity, directly proportionate to worth as measured by fitness to the conditions of existence. Furthermore, though the species is made up of individuals, many of these individuals may disappear and the species still be preserved, whereas its disappearance as a whole involves absolute failure in achieving the end, so that, where preservation of individuals conflicts with preservation of the species, the individuals must be sacrificed. The principle that among adults benefits must be in proportion to merits, implies in its biological aspect survival of the fittest. Its violation involves double harm to the species by sacrifice of the superior to the inferior, and consequent increase of the inferior. "Interpreted in ethical terms, it is that each individual ought to be subject to the effects of its own nature and resulting conduct"; and throughout sub-human life this rule holds without qualification. The same principle is displayed in the mutual relations of the parts of organisms, every part being nourished in proportion to its use or function, a balancing of the relative powers of the parts being thus effected, and the organism "fitted as a whole to its existence by having its parts continuously proportioned to the requirements." In a parallel manner, the species as a whole is fitted to its environment by the greater prosperity to self and offspring that comes to those better adapted. But sub-human justice is extremely imperfect, alike in general and in detail.