132 THE DOCTRINE OF DESCENT, 
opponents of the great inquirer endeavour to suppress 
his merits and authority by maintaining that he is pro- 
perly a mere dilettante, dealing with general abstrac- 
tions,** a stranger to the keen observation which takes 
full account of facts. How Darwin arrived at the idea 
which has made an epoch in science, he has himself 
made known in the introduction to his first work on 
the doctrine of Descent, namely, the “Origin of 
Species ;”” and in more detail in a letter to Haeckel, 
published by the latter in his “ History of Creation” 
(Natiirlichen Schépfungsgeschichte). 
“Having reflected much on the foregoing facts, it 
seemed to me probable that allied species were de- 
scended from a common ancestor. But during several 
years I could not conceive how each form could have 
been modified so as to become admirably adapted to 
its place in nature. I began, therefore, to study do- 
mesticated animals and cultivated plants, and after 
a time perceived that man’s power of selecting and 
breeding from certain individuals was the most power- 
ful of all means in the production of new races. Having 
attended to the habits of animals and their refations to 
the surrounding conditions, I was able to realize the 
severe struggle for existence to which all organisms are 
subjected ; and my geological observations had allowed 
me to appreciate to a certain extent the duration of 
past geological periods. With my mind thus prepared 
I fortunately happened to read Malthus’s “Essay on 
Population ;” and the idea of natural selection through 
the struggle for existence at once occurred tome. Of 
all the subordinate points in the theory, the last which 
I understood was the cause of the tendency in the 
