Now the inborn characters (excepting modifications _in utero_) are admittedly heritable, for inborn characters must exist potentially in the germ-plasm. The belief that acquired characters are also inherited, therefore, involves belief that in some way the trait acquired by the parent is incorporated in the germ-plasm of the parent, to be handed on to the child and reappear in the course of the child's development. The impress on the parental _body_ must in some way be transferred to the parental _germ-plasm_; and not as a general influence, but as a specific one which can be reproduced by the germ-plasm. This idea was held almost without question by the biologists of the past, from Aristotle on. Questionings indeed arose from time to time, but they were vague and carried no weight, until a generation ago several able men elaborated them. For many years, it was the question of chief dispute in the study of heredity. The last word has not yet been said on it. It has theoretical bearings of immense importance; for our conception of the process of evolution will be shaped according to the belief that acquired characters are or are not inherited. Herbert Spencer went so far as to say, "Close contemplation of the facts impresses me more strongly than ever with two alternatives--either that there has been inheritance of acquired characters, or there has been no evolution." But its practical bearings are no less momentous. Again to quote Spencer: "Considering the width and depth of the effects which the acceptance or non-acceptance of one or the other of these hypotheses must have on our views of life, the question, Which of them is true? demands beyond all other questions whatever the attention of scientific men. A grave responsibility rests on biologists in respect of the general question, since wrong answers lead, among other effects, to wrong belief about social affairs and to disastrous social actions." Biologists certainly have not shirked this "grave responsibility" during the last 30 years, and they have, in our opinion, satisfactorily answered the general question. The answer they give is not the answer Herbert Spencer gave.