216 ADAPTATION AND PROGRESS 
brain. The plastic period of adolescence, lengthened in civilized 
man until it has come to cover more than one-third of his life- 
time, is thus the guaranty of his boundless progressiveness. . . .! 
In its crude beginnings the psychical life was but an appendage 
to the body, in fully-developed humanity the body is but the 
vehicle for the soul.” ? 
Fiske goes on to show the necessity of prolongation of infancy 
with the development of higher forms of animal life, in order that 
the organism may adjust itself to the ever increasing complexity 
of its environment. In lower forms the reactions are automatic 
or instinctive, but such are not sufficient for higher forms which 
must learn by experience, and a prolonged infancy affords a 
period of training so that when independent life is entered upon 
the organism will have a fair chance of survival. ‘ While the 
nervous connections accompanying a simple intelligence are 
already organized at birth,” he says, ‘“‘ the nervous connections 
accompanying a complex intelligence are chiefly organized after 
birth. . . . Infancy, psychologically considered, is the period 
during which the nerve connections and correlative ideal associa- 
tions necessary for self-maintenance are becoming permanently 
established. Now this period, which only begins to exist when 
the intelligence is considerably complex, becomes longer and 
longer as the intelligence increases in complexity. In the human 
race it is much longer than in any other race of mammals, and it is 
much longer in the civilized man than in the savage.” 3 
According to our author this prolongation of infancy had a 
profound sociological effect in uniting the parents in a more 
permanent family life required for the protection of the helpless 
infant, in this way developing sympathy, the basis of sociality. 
“ Thus we cross the chasm which divides animality from human- 
ity, gregariousness from sociality, hedonism from morality, the 
sense of pleasure and pain from the sense of right and wrong.” 4 
The prolongation of infancy is of vital importance, then, not only 
in the development of the nervous system and its acquirement of 
modes of activity making for adaptation, but in the establish- 
1 Destiny of Man, pp. 30, 56. 8 Cosmic Philosophy, ii, p. 342. 
2 Tbid., p. 65. 4 Tbid., p. 346. 
