§ 70. Under its biological aspect this proposition cannot be contested by those who agree in the doctrine of Evolution; but probably they will not at once allow that admission of it under its ethical aspect is equally unavoidable. While, as respects development of life, the well-working of the universal principle described is sufficiently manifest; the well-working of it as respects increase of happiness may not be seen at once. But the two cannot be disjoined. Incapacity of every kind and of whatever degree causes unhappiness directly and indirectly--directly by the pain consequent on the overtaxing of inadequate faculty, and indirectly by the non-fulfillment, or imperfect fulfillment, of certain conditions to welfare. Conversely, capacity of every kind sufficient for the requirement conduces to happiness immediately and remotely--immediately by the pleasure accompanying the normal exercise of each power that is up to its work, and remotely by the pleasures which are furthered by the ends achieved. A creature that is weak or slow of foot, and so gets food only by exhausting efforts, or escapes enemies with difficulty, suffers the pains of over-strained powers, of unsatisfied appetites, of distressed emotions; while the strong and swift creature of the same species delights in its efficient activities, gains more fully the satisfactions yielded by food as well as the renewed vivacity this gives, and has to bear fewer and smaller pains in defending itself against foes or escaping from them. Similarly with duller and keener senses, or higher and lower degrees of sagacity. The mentally-inferior individual of any race suffers negative and positive miseries; while the mentally-superior individual receives negative and positive gratifications. Inevitably, then, this law in conformity with which each member of a species takes the consequences of its own nature; and in virtue of which the progeny of each member, participating in its nature, also takes such consequences; is one that tends ever to raise the aggregate happiness of the species, by furthering the multiplication of the happier and hindering that of the less happy. All this is true of human beings as of other beings. The conclusion forced on us is that the pursuit of individual happiness within those limits prescribed by social conditions, is the first requisite to the attainment of the greatest general happiness. To see this it needs but to contrast one whose self-regard has maintained bodily well-being, with one whose regardlessness of self has brought its natural results; and then to ask what must be the contrast between two societies formed of two such kinds of individuals.