2 66 THE POPULAR SCIENCE MONTHLY 



largely at the bottom of the denial of any role whatsoever to the in- 

 stincts 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, ac- 

 cordingly, 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 modi- 

 fiable 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 connec- 

 tions 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 multi- 

 tude 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 evi- 

 dently the psychological aspect of racial heredity, and it is as incon- 

 ceivable that the organic individual should exist without them as with- 

 out 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 biolog- 

 ical characteristics of the stock also vary. Inasmuch as they are char- 

 acteristics of the highest and most unstable portion of the organism, the 

 nervous system, they probably vary more widely than the grosser phys- 

 ical 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. 



