ment and organization, to the direct influences it exerts by furnishing an adequate theory of the social unit—Man. For, while Biology is mediately connected with Sociology by a certain parallelism between the groups of phenomena they deal with, it is immediately connected with Sociology by having within its limits this creature whose properties originate social evolution. The human being is at once the terminal problem of Biology and the initial factor of Sociology.
If Man were uniform and unchangeable, so that those attributes of him which lead to social phenomena could be learned and dealt with as constant, it would not much concern the sociologist to make himself master of other biological truths than those cardinal ones above dwelt upon. But, since, in common with every other creature, Man is modifiable—since his modifications, like those of every other creature, are ultimately determined by surrounding conditions—and since surrounding conditions are in part constituted by social arrangements—it becomes requisite that the sociologist should acquaint himself with the laws of modification to which organized beings in general conform. Unless he does this he must continually err, both in thought and deed. As thinker, he will fail to understand the continual action and reaction of institutions and character, each slowly modifying the other through successive generations. As actor, his furtherance of this or that public policy, being unguided by a true theory of the effects wrought on citizens, will probably be mischievous rather than beneficial; since there are more ways of going wrong than of going right. How needful is enlightenment on this point will be seen, on remembering that scarcely anywhere is attention given to the modifications which a new agency, political or other, will produce in men's natures. Immediate influence on actions is alone contemplated, and the immeasurably more important influence on the bodies and minds of future generations is wholly ignored.
Yet the biological truths which should check this random political speculation and rash political action are conspicuous, and might, one would have thought, have been recognized by every one, even without special preparation in Biology. That faculties and powers of all orders, while they grow by exercise, dwindle when not used, and that alterations of nature descend to posterity, are facts continually thrust on men's attention, and more or less admitted by all. Though the evidence of heredity, when looked at in detail, seems obscure, because of the multitudinous differences of parents and of ancestors, which all take their varying shares in each new product, yet, when looked at in the mass, the evidence is overwhelming. Not to dwell on the countless proofs furnished by domesticated animals of many kinds as modified by breeders, the proofs furnished by the human races themselves are amply sufficient. That each variety of man goes on so reproducing itself that adjacent generations are nearly alike, however appreciable may sometimes be the divergence in a long series of gen-