Experimental Study of Growth 249 
the structure and functions of an organism are adapted to its en- 
vironment,”’ i.e. by natural selection of individual differences. 
Weismann believes that “in regulating the duration of life, 
the advantage to the species, and not alone to the individual, is 
of any importance.” The purpose of the individual is the per- 
petuation of the species, and its length of life has been regulated 
accordingly. As soon as the individual has performed this 
purpose, it “has fulfilled its duty” and may die.? 
Weismann believes that death is essential to the species, be- 
cause the individuals become injured and must be replaced by 
new and more perfect forms. From this, he says, follows the 
necessity of reproduction and the utility of death. He points 
out that worn-out individuals are even harmful to the species, 
for they consume the food that sound and reproducing indi- 
viduals might make use of. Death ‘is not a primary necessity 
but . . . has been secondarily acquired as an adaptation.” 
Plausible as this conclusion may be made to appear when 
stated in this abstract and general way, it will not, I believe, bear 
critical examination. Without attempting an elaborate refuta- 
tion of Weismann’s conclusion the following objections may be 
briefly stated :— 
(1) To put the problem of senescence and death in a different 
category from other physiological processes, seems entirely arbi- 
trary. Weismann’s contention that death has been imposed 
upon each species not by internal physiological changes, but 
from without by natural selection, is not only paradoxical, as he 
states, but it seems to me a confused point of view. 
(2) Is it not putting the cart in front of the horse to argue that 
the length of life is adjusted to the power of reproduction? 
It seems more reasonable to assume, if we must make some as- 
sumption, that if there is any connection between the two things, 
the length of life determines in a general way the cessation of re- 
production; for the general decline that leads finally to a “‘natu- 
ral death”? may at its inception affect the reproductive organs. 
1 This includes the idea not only of giving birth to the new individuals, but 
in some cases caring for them or in protecting them during their immaturity. 
