It may be impossible to prove that there ever was a uniform primitive state. "So long as we are within the sphere of experience," says Starcke, "we cannot begin by assuming that there was at any time only a single human community. Experience begins with a plurality of communities, and the single community of which we are in search must be found on the indeterminate boundary between man and animals."[267] Indeed, it seems certain that if we are ever to understand the character of the earliest forms of human marriage and the human family, we must begin by studying the family and marriage as they exist among other and less advanced members of the animal world.[268] Biology, declares Letourneau, is the starting-point of sociology.[269] In this view Starcke coincides. "We have no reason to regard the social life of man as a recent form. Not only do the same psychical forces which influence gregarious man also influence the gregarious animal; probability also leads us to infer that the primitive communities of mankind are derived from those of animals. Since man in so many respects only goes on to develop the previous achievements of animal experience, it may be supposed that he made use of the social experience of animals as the firm foundation of his higher advancement." Besides, "there are human communities which are far less firmly established than those of animals;" and "it may even be asserted that the social faculty is positive in animals and negative in man," for man is "less subservient to instinct."[270] "If we want to find out the origin of marriage," says Westermarck, "we have to strike into another path, the only one which can lead to the truth, but a path which is open to him alone who regards organic nature as one continued chain, the last and most perfect link of which is man. For we can no more stop within the limits of our own species, when trying to find the root of our psychical and social life, than we can understand the physical condition of the human race without taking into consideration that of the lower animals."[271] [267] _Primitive Family_, 7, 8. [268] See LETOURNEAU, _L'évolution du mariage_, chap. ii, on "Le mariage et la famille chez les animaux;" and his _Sociology_, 327-30, 380-82. [269] _L'évolution du mariage_, chap. i. [270] STARCKE, _op. cit._, 8, 9. [271] _Human Marriage_, 9. See also _ibid._, chap. iii, on the "Antiquity of Human Marriage." Accordingly three principal arguments against the existence at any time of a general state of promiscuity have been advanced: