It is thus impossible to tell as yet with any security or precision the biological components of any single mental trait. The evidence at our disposal, however, does confirm us in the belief that one of the most significant and certain causes of individual differences, whether physical or mental, is immediate ancestry or family. Individuals are made by what they are initially, and, as we shall presently see, therefore largely by their inheritance. With the latter, environment can do just so much, and no more. And the most significant and effective part of an individual's inheritance is his family for some generations back, rather than the race to which he belongs. THE INFLUENCE OF THE ENVIRONMENT. Those factors so far discussed which determine individual differences are independent of the particular conditions of life in which an individual happens to be placed. An individual's race, sex, family are beyond modification by anything that happens to him after birth. Maturity, in so far as it is mere growth independent of training, is also largely a fixed and unmodifiable condition. The original nature, determined by race, sex, and immediate ancestry, with which a man starts life is subject to modification by his social environment, by the ideas, customs, companions, beliefs, by which he is surrounded, and with which he comes continuously in contact. Commonly the influence of environment is held to be very high. It is difficult, however, accurately to distinguish between effects which are due to original nature and effects which are due to environment. Differences in training are important, but the results vary with the natures trained. Precisely the same environment will not have the same consequences for two different natures. Two approximately same natures will show something like the same effects in dissimilar environments. Human beings are certainly differentiated by the customs, laws, ideals, friends, and occupations to which they are exposed. But what the net result will be in a specific case, depends on the individual's equipment to start with, an equipment that is fixed before the environment has had a chance to act at all. The kindliness and indulgence that save some children demoralize others. In some people a soft answer turneth away wrath; in others it will kindle it. Andrew Carnegie starts as a bobbin boy, and becomes a millionaire; but there were many other bobbin boys. The sunset that stirs in one man a lyric, leaves another cold. The same course in biology arouses in one student a passion for a life of science; it leaves another hoping never to see a microscope again. On the other hand, the same types of original capacity thrown into different environments will yet attain somewhat comparable results, in the way of character and achievement. The biographies of a few poets, painters, philosophers, and scientists chosen at random, show the most diverse antecedents.[1]