tween their mental and moral processes and their modes
of exhibiting them and our own; while visits were made by him to the
Zoological Gardens with the same object. By reading and correspondence
also, an enormous mass of notes was collected, and on February 4th,
1868, having seen his great work on Variation under Domestication
published, Darwin was able to make the entry in his diary, 'Began work
on Man.'

As was usual with most of his works, Darwin underestimated the time
required to complete it. Through all the years 1867--'68, '69 and '70 we
find the entries in his diary 'working at _Descent of Man_,' and only
early in the year 1871 was the book finished. His original plan of
compressing his notes on the expression of the Emotions into a chapter
at the end of the book proved to be impracticable, and the material was
reserved for a new work. This work, _The Expression of the Emotions in
Man and Animals_, was commenced directly the _Descent of Man_ was out of
hand, a rough copy was finished by April 27th, 1871, but the last proofs
were not corrected till August 23rd, 1873.

In dealing with the question of the origin of the human race, Darwin
was led to propound his views concerning Sexual selection, the results
of the preferences shown by males and females, respectively, not only
among mankind, but in various other animals. It was with respect to some
of the conclusions contained in this work that Wallace found himself
unable to follow Darwin. Wallace maintained that while man's body could
have been developed by Natural Selection, his intellectual and moral
nature must have had a different origin. He also declined to adopt the
theory of sexual selection, so far as it depends on preferences
exhibited by females for beauty in the males. Wallace, however, in some
respects has always been disposed to attach more importance to Natural
Selection, as the greatest, if not the only factor in evolution, than
Darwin himself.

It will be seen that although Darwin had in all probability thought out
all his important theoretical conclusions before 1869, when he reached
the 'fatal age,' yet, owing to various delays, the books, in which he
embodied his views, had not all appeared till more than four years
later.

Lyell, who was a convinced evolutionist before the publication of the
_Principles of Geology_, as is shown by his letters,--and the fact is
strongly insisted on both by Huxley and Haeckel[141],--was slow in
coming into _