which was, in reality, nothing but a further development of the
ideas expressed by Darwin himself in The Descent of Man--seemed
to me so correct and of so great an importance, that since I
became acquainted with it (in 1883) I began to collect materials
for further developing the idea, which Kessler had only cursorily
sketched in his lecture, but had not lived to develop. He died in
1881.

In one point only I could not entirely endorse Kessler's
views. Kessler alluded to "parental feeling" and care for progeny
(see below, Chapter I) as to the source of mutual inclinations in
animals. However, to determine how far these two feelings have
really been at work in the evolution of sociable instincts, and
how far other instincts have been at work in the same direction,
seems to me a quite distinct and a very wide question, which we
hardly can discuss yet. It will be only after we have well
established the facts of mutual aid in different classes of
animals, and their importance for evolution, that we shall be
able to study what belongs in the evolution of sociable feelings,
to parental feelings, and what to sociability proper--the
latter having evidently its origin at the earliest stages of the
evolution of the animal world, perhaps even at the
"colony-stages." I consequently directed my chief attention to
establishing first of all, the importance of the Mutual Aid
factor of evolution, leaving to ulterior research the task of
discovering the origin of the Mutual Aid instinct in Nature.

The importance of the Mutual Aid factor--"if its generality
could only be demonstrated"--did not escape the naturalist's
genius so manifest in Goethe. When Eckermann told once to Goethe--