But the inequality of species cannot be adopted as the calculative basis of comparative virtue in the evolutionary scale, since the relative positions of organisms can only be determined by an examination of the degree of consciousness possessed by each in comparison with the others. For instance, although we say that a horse is a more highly organised creature than a rabbit, meaning thereby that according to our estimation he presents a more complicated mechanism, yet such a comparison of physical susceptibility is necessarily imperfect, because limited by the degree of our own discrimination. For since the correctness of our judicial opinions rests upon our ability properly to appreciate the true relation between intelligences and their environments different from our own, it follows that our criticism of their comparative complexity can be no criterion of intrinsic individual merit. The same inadequacy of human judgment applies to any attempt to estimate the degree of spiritual consciousness possessed by various organisms.[28] Such endeavour may be successful in establishing a comparative standard for a rational criticism of religious creeds in their relation to physical evolution; but it is powerless to affix a stationary standard of morality to differently constructed intelligences. The possession by creatures of faculties differing from those of others does not necessarily make for superiority or inferiority. That is to say, differentiation of type does not determine merit. A man is not superior to a horse because his structure and powers are unlike those of the horse; nor is a rabbit or a bird inferior either to a horse or to a man, since the organisation of all these creatures is adapted to different usage. Thus, the possession of a highly specialised brain does not in itself make of man a superior order of creation. The use or abuse of faculties, and the obedience or disobedience to the laws of being, offer the only standard by which the comparative superiority, inferiority, or equality of creatures of different organisation can be fairly estimated.[29] And only by a similar comparison of the response to spiritual environment displayed by the followers of religious creeds can an approximate idea of their value be formed.