largely at the bottom of the denial of any rôle whatsoever to the instincts in human social life. Drawing their conceptions of instinct from a crude animal psychology, many social thinkers seem to conceive of instinct as something hard and fast, as a definite, "crystallized" mode of activity, such as we find, to be sure, in the lower reaches of animal life, especially among the insects. Such thinkers conceive, accordingly, instinct as having something fatalistic and inevitable about it. But practically all psychologists are now united in repudiating such a conception of instinct. The instincts of all the higher animals, man included, are not of this hard and fast and definite type, but are modifiable through training and experience in many ways, even though they are influential in determining animal behavior. Let us see then what conception of instinct modern psychology has worked out. In man, as in all the higher animals, there is a highly developed nervous system, with multitudes of connections between its elements. These connections are pathways of nervous currents. Many of these connections are inborn and seem to be as much a part of the heredity of the individual and the race as stature, the color of eyes and hair, or any other physical characteristic. Hence the nervous system is characterized by a multitude of more or less perfectly developed preorganized reactions which are a part of the individual's heredity. These preorganized reactions have been established through the operation of selection, biologists tell us, upon variations in the hereditary elements, in the same way in which the bodily characteristics of the species have been established. In all the higher animals, and especially in man, on account of the complexity of his nervous system, these native reactions are not fixed and unalterable, but are subject in a large degree to modification or elimination according to changes in the environment. Nor are they always specific but they are often, as Thorndike says, indefinite and general.
Instincts are then inborn pathways of nervous currents, which have as their functional correlate inborn motor tendencies, and as their psychical correlate inborn psycho-physical dispositions. They are evidently the psychological aspect of racial heredity, and it is as inconceivable that the organic individual should exist without them as without the equipment or general bodily structure itself. As instincts are not acquired by the individual, but are given in the germ, they are transmitted from generation to generation, varying only as other biological characteristics of the stock also vary. Inasmuch as they are characteristics of the highest and most unstable portion of the organism, the nervous system, they probably vary more widely than the grosser physical traits. They are more modifiable and alterable, owing to the fact that only about one third of the connections in the nervous system are made at birth, the other two thirds being acquired by the individual
- Op. cit., pp. 189-190.