Origin of Different Kinds of Adaptations 379 
Nevertheless, it seems to be true in the case of morphine and 
of arsenic, and probably for some other substances as well, 
that if their use is suddenly stopped the individual may die 
in consequence. In this respect the organism behaves ex- 
actly as it does to an environment to which it has become 
adapted. 
REGENERATION 
Many animals are able to replace lost parts, and all of 
them can heal wounds and mend injuries. This power is 
obviously of great advantage to them, and it has been sup- 
posed by Darwin, and more especially by his followers, that 
the power has been acquired through natural selection. It 
is not difficult to show that regeneration could not, in many 
cases, and presumably in none, have been acquired in this 
way. Since I have treated this subject at some length 
recently in my book on “Regeneration,” I shall attempt to 
do no more here than indicate the outline of the argument. 
The Darwinians believe that, if some individuals of a 
species have the power to replace a part that is lost better 
than have other individuals, it would follow that those would 
survive that regenerate best, and in this way after a time the 
power to regenerate perfectly would be acquired. 
But the matter is by no means so simple as may appear 
from this statement. In the first place, it is a matter of 
common observation that all the individuals of a species are 
never injured in the same part of the body at the same time. 
In those cases in which it is known that a special part is 
often injured, an examination has shown that there are not 
more than ten per cent of individuals that are injured at any 
one time, and in the case of the vast majority of animals 
this estimate is much too great. Thus there will be very 
little chance for competition of the injured individuals in 
each generation with each other, and the effects that are 
imagined to be gained as a result would be entirely lost 
