V 
NATURAL SELECTION 
105 
Divergence of Character . 
In species which have a wide range the struggle for exist¬ 
ence w ill often cause some individuals or groups of individuals 
to adopt new habits in order to seize upon vacant places in 
nature where the struggle is less severe. Some, living among 
extensive marshes, may adopt a more aquatic mode of life ; 
others, living where forests abound, may become more arboreal. 
In either case we cannot doubt that the changes of structure 
needed to adapt them to their new habits would soon be 
brought about, because we know that variations in all the 
external organs and all their separate parts arc very abundant 
and are also considerable in amount. That such divergence of 
character has actually occurred we have some direct evidence. 
Mr. Darwin informs us that in the Catskill Mountains in the 
United States there are two varieties of wolves, one with a 
light greyhound-like form which pursues deer, the other more 
bulky with shorter legs, which more frequently attacks sheep . 1 
Another good example is that of the insects in the island of 
Madeira, many of which have either lost their wings or have 
had them so much reduced as to be useless for bight, while the 
very same species on the continent of Europe possess fully 
developed wings. In other cases the wingless Madeira species 
are distinct from, but closely allied to, winged species of Europe. 
The explanation of this change is, that Madeira, like many 
oceanic islands in the temperate zone, is much exposed to 
sudden gales of wind, and as most of the fertile land is on the 
coast, insects which Hew much would be very liable to be 
blown out to sea and lost. Year after year, therefore, those 
individuals which had shorter wings, or which used them least, 
were preserved ; and thus, in time, terrestrial, wingless, or im¬ 
perfectly winged races or species have been produced. That 
this is the true explanation of this singular fact is proved by 
much corroborative evidence. There are some few flower- 
frequenting insects in Madeira to whom wings are essential, 
and in these the wings are somewhat larger than in the same 
species on the mainland. AYe thus see that there is no general 
tendency to the abortion of wings in Madeira, but that it is 
simply a case of adaptation to new conditions. Those insects 
1 Origin of Species, p. 71. 
