250 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
butterfly, Kallima, previously described (pp. 201, 202). In its present 
condition this animal has a strikingly detailed resemblance to a dried 
leaf, which is therefore doubtless of some value. But of what value 
would be the first tiny change in the direction of resemblance? Until 
its resemblance became close enough actually to deceive the enemies of 
butterflies, the critics claim, there would be no chance for selection to act. 
8. It is frequently objected that a vast number of characters of 
organs are useless or non-adaptive and, as such, could not have arisen 
through the instrumentality of natural selection. If these useless 
characters, which are sometimes quite large and prominent, are 
independent of natural selection, why do we need natural selection to 
explain adaptive characters? It is also claimed that a vast number 
of specific peculiarities are useless and therefore could not have helped 
in the differentiation of species. It should be said in defense that 
Darwin realized this difficulty quite as clearly as do his critics and 
was greatly puzzled by it. His idea of correlated variability, however, 
helps to answer it, for it may well be that many of these apparently 
useless characters are correlated, or linked in inheritance, with charac- 
ters of supreme selective value such as general hardiness or great 
fecundity. Darwin also points out that we are not in a position at 
present to pronounce judgment on the value of many structures or 
functions that have been adjudged non-adaptive. 
g. Certain characters in organisms, past and present, have been 
interpreted as overspecializations, organs that have evolved beyond 
the range of usefulness or that are more elaborate than is demanded 
for survival under the conditions of life. The case of the extinct Irish 
elk is often cited as an example of overspecialization. This group of 
animals went to extremes in the development of size and elaboration 
of horns far beyond the range of usefulness, so that it is said to have 
brought about the extinction of the race. Natural selection, which is 
supposed to have brought the horns up to the point of adaptive 
perfection, should have kept them within the bounds of usefulness. 
Again, the enormously overgrown and overspecialized dinosaurs 
of long ago are thought of as having followed their lines of evolution 
far beyond the point of greatest effectiveness and adaptability. 
io. The rudimentation of structures, which is such a common 
phenomenon in nature, is said to meet with no adequate explanation 
on a selection basis. The case of the whale’s vestigial hind limbs is 
a case in point. Darwin’s explanation would be that under aquatic 
conditions the first whale ancestors would be handicapped by hind 
