There is "only one scientific method, the method of the natural sciences,"[433] and we apply this method also "in the sciences that relate to man,"[434] particularly in the "science of society."[435] Now, a mighty revolution is at present taking place[436] in the entire realm of science; it is the result of the "philosophy of evolution."[437] "The idea hitherto prevalent, that everything in nature stands fast, is fallen, destroyed, annihilated. Everything in nature changes; nothing remains: neither the rock which appears to us to be immovable and the continent which we call _terra firma_, nor the inhabitants, their customs, habits, and thoughts. All that we see about us is a transitory phenomenon, and must change, because motionlessness would be death."[438] In the case of organisms this evolution is progress, in consequence of "their admirable adaptivity to their conditions of life. They develop such faculties as render more complete both the adaptations of the aggregates to their surroundings and those of each of the constituent parts of the aggregate to the needs of free co-operation."[439] "This is the 'struggle for existence,' which, therefore, must not be conceived merely in its restricted sense of a struggle between individuals for the means of subsistence."[440] "Evolution never advances so slowly and evenly as has been asserted. Evolution and revolution alternate, and the revolutions--that is, the times of accelerated evolution--belong to the unity of nature just as much as do the times in which evolution takes place more slowly."[441] "Order is the free equilibrium of all forces that operate upon the same point; if any of these forces are interfered with in their operation by a human will, they operate none the less, but their effects accumulate till some day they break the artificial dam and provoke a revolution."[442] Kropotkin applies these general propositions to the social life of men.[443] "A society is an aggregation of organisms trying to combine the wants of the individual with those of co-operation for the welfare of the species";[444] it is "a whole which serves toward the purpose of attaining the largest possible amount of happiness at the least possible expense of human force."[445] Now human societies evolve,[446] and one may try to determine the direction of this evolution.[447] Societies advance from lower to higher forms of organization;[448] but the goal of this evolution--that is, the point towards which it directs itself--consists in "establishing the best conditions for realizing the greatest happiness of humanity."[449] What we call progress is the right path to this goal;[450] humanity may for the time err from this path, but will always be brought back to it at last.[451]