442 
DARWINISM 
CHA1>. 
Much of the mystery of instinct arises from the persistent 
refusal to recognise the agency of imitation, memory, observa¬ 
tion, and reason as often forming part of it. Yet there is 
ample evidence that such agency must be taken into account. 
Both Wilson and Leroy state that young birds build inferior 
nests to old ones, and the latter author observes that the best 
nests are made by birds whose young remain longest in the 
nest. So, migration is now well ascertained to be effected by 
means of vision, long flights being made on bright moonlight 
nights when the birds fly very high, while on cloudy nights 
they fly low, and then often lose their way. Thousands 
annually fly out to sea and perish, showing that the instinct 
1 to migrate is imperfect, and is not a good substitute for reason 
and observation. 
Again, much of the perfection of instinct is due to the 
extreme severity of the selection during its development, any 
failure involving destruction. The chick which cannot break 
the eggshell, the caterpillar that fails to suspend itself properly 
or to spin a safe cocoon, the bees that lose their way or that 
fail to store honey, inevitably perish. So the birds that fail 
to feed and protect their young, or the butterflies that lay 
their eggs on the wrong food-plant, leave no offspring, and 
the race with imperfect instincts perishes. Now, during the 
long and very slow course of development of each organism, 
this rigid selection at every step of progress has led to the 
preservation of every detail of structure, faculty, or habit that 
lias been necessary for the preservation of the race, and has 
thus gradually built up the various instincts which seem so 
marvellous to us, but which can yet be shown to be in many 
cases still imperfect. Here, as everywhere else in nature, we 
find comparative, not absolute perfection, with every gradation 
from what is clearly due to imitation or reason up to what 
seems to us perfect instinct— that in which a complex action 
is performed without any previous experience or instruction. 1 
1 Weismann explains instinct on similar lines, and gives many interesting 
illustrations (see Essays on Heredity). He holds “that all instinct is entirely 
due to the operation of natural selection, and has its foundation, not upon 
inherited experiences, but upon variations of the germ.” Many interesting 
and difficult cases of instinct are discussed by Darwin in Chapter VIII of the 
Origin of Species, which should be read in connection with the above remarks. 
Since this chapter was written my attention has been directed to Mr. 
