The evolutionist explanation of the natural world as applied to sociology found its fullest exponent in Herbert Spencer (1820-1903), who studied the anatomy of the social frame. He derived the principles of sociology from the principles of psychology and of biology, and regarded social development as a super-organic evolution. But all these earlier attempts to discover a social science were speculative rather than practical. The solid foundations of inductive sociology were laid by Bachofen, Morgan, J. F. McLennan, and others. [Sidenote: =Bachofen, Morgan, McLennan, and others.=] Bachofen (1861) was the first to study the system of filiation through the mother, or mother-right, which was widely distributed among ancient peoples, and still occurs in many regions in a more or less developed condition. McLennan frankly states that “the honour of that discovery, the importance of which, as affording a new starting-point for all history, cannot be over-estimated, must, without stint or qualification, be assigned to him” (1876, p. 421). Independently, however, J. F. McLennan (1827-1881), in his _Primitive Marriage_ (1865), arrived at the conclusion “that the most ancient system in which the idea of blood-relationship was embodied was a system of kinship through females only.”[102] He points out more than once that “Mr. Maine seems not to have been able to conceive of any social order more primitive than the patriarchal.”[103] This book was reprinted with additions in 1876, and his two other books were published posthumously (1885, 1896). In these and more fugitive writings McLennan was a keen controversialist, and with unnecessary vigour and animus attacked Morgan, Sir Henry Maine, and Dr. Howitt. McLennan’s attitude may be partly explained by the fact that he was a lawyer and a theorist, but he possessed great enthusiasm, with which he infused those who came into contact with him, and his labours served to advance the study of sociology. Footnote 102: P. 124 of 1876 ed. Footnote 103: P. 181, _ibid._ “From the time of Plato downwards, theories of human society have been current in which the family living under the headship of a father is accepted as the ultimate social unit. These theories have taken various shapes ... with Sir Henry Maine (_Ancient Law_, 1861) the theory becomes a theory of the origin of society, or at least of the earliest stage of society in which Comparative Jurisprudence is called upon to take interest.”[104] Footnote 104: D. McLennan, _The Patriarchal Theory_, 1885, p. x.