We may note at the beginning, however, that the word _evolution_ has two distinct, though related, meanings. First, it usually means Darwin's doctrine of descent; secondly, it is used to designate Spencer's theory of universal evolution. Let us note somewhat in detail what evolution means in the first of these senses. The Darwinian Theory of Descent.--Darwin's theory of descent is the doctrine that all forms of life now existing or that have existed upon the earth have sprung from a few simple primitive types. According to this theory all forms of animals and plants have sprung from a few primitive stocks, though not necessarily one, because even in the beginning there may have existed a distinction at least between the plant and the animal types. So far as the animal world is concerned, then, this theory amounts to the assertion of the kinship of all life. From one or more simple primitive unicellular forms have arisen the great multitude of multicellular forms that now exist. Popularly, Darwin's theory is supposed to be that man sprang from the apes, but this, strictly speaking, is a misconception. Darwin's theory necessitates the belief, not that man sprang from any existing species of ape, but rather that the apes and man have sprung from some common stock. It is equally true, however, that man and many other of the lower animals, according to this theory, have come from a common stock. As was said above, the theory is not a theory of the descent of man from any particular animal type, but rather the theory of the kinship, the genetic relationship, of all animal species. It is evident that if we assume Darwin's theory of descent in sociology we must look for the beginnings of many peculiarly human things in the animal world below man. Human institutions, according to this theory, could not be supposed to have an independent origin, or human society in any of its forms to be a fact by itself, but rather all human things are connected with the whole world of animal life below man. Thus if we are, according to this theory, to look for the origin of the family, we should have to turn first of all to the habits of animals nearest man. This is only one of the many bearings which Darwin's theory has upon the study of social problems; but it is evident even from this that it revolutionizes sociology. So long as it was possible to look upon human society as a distinct creation, as something isolated, by itself in nature, it was possible to hold to intellectualistic views of the origin of human institutions.