But the popular mind frequently lags a generation behind, in its grasp of the work of science, and it must be said that in this case the popular mind is still largely under the influence of Herbert Spencer and his school. _Whether they know it or not_, most people who have not made a particular study of the question still tacitly assume that the acquirements of one generation form part of the inborn heritage of the next, and the present social and educational systems are founded in large part on this false foundation. Most philanthropy starts out unquestioningly with the assumption that by modifying the individual for the better, it will thereby improve the germinal quality of the race. Even a self-styled eugenist asks, "Can prospective parents who have thoroughly and systematically disciplined themselves, physically, mentally and morally, transmit to their offspring the traits or tendencies which they have developed?" and answers the question with the astounding statement, "It seems reasonable to suppose that they have this power, it being simply a phase of heredity, the tendency of like to beget like." The right understanding of this famous problem is therefore fraught with the most important consequences to eugenics. The huge mass of experimental evidence that has been accumulated during the last quarter of a century has, necessarily, been almost wholly based on work with plants and lower animals. Even though we can not attempt to present a general review of this evidence, for which the reader must consult one of the standard works on biology or genetics, we shall point out some of the considerations underlying the problem and its solution.