54 ANIMAL ACTIVITIES. 
it is not closely related in structure or in mode of 
growth (Figs. 54 and 55). 
Such imitations of other animals less likely to suffer 
from enemies are common throughout the animal king- 
dom. In these cases, neither the mimic nor the animal 
mimicked is supposed to act consciously. No intelli- 
gence on the part of the animal itself is shown by such 
mimicry, for even if it intelligently wished to change 
its color, no butterfly could do so. 
The theory which is now generally believed by 
scientists to account for these protective devices and 
the thousands of others that have been observed may 
be briefly illustrated by considering the family history 
of the moth whose wings resemble birch-bark. 
Natural Selection. It is supposed that the earlier 
members of this family did not have the outer wings 
so marked, but that from a brood of caterpillars there 
hatched moths like the parent moths, yet varying to 
some extent on account of unknown causes. Some of 
these varying moths had markings on the outer wings 
which made them resemble in some slight degree the 
birch-tree on which they were accustomed to alight. 
It is evident that these protected moths would be less 
likely to be eaten than those not resembling the birch- 
tree; hence they would be preserved to deposit eggs, 
while their less fortunate brothers and sisters would be 
eaten. The next brood of moths, resembling their 
parents as they must, would be likely to include a 
greater number of protected individuals, and probably 
some even better protected than their parents. Those 
best protected would be allowed to produce offspring, 
while the less favored would be destroyed. In this 
way after many generations the protective resemblance 
becomes more and more pronounced. This process 
has been called ‘‘ natural selection’’. It is thought 
to explain many of the changes which have taken place 
in the history of both animals and plants. It is easy 
to see that there is really no rational selection on the 
