circumstances. On my return I continued slowly writing. By August
1877 I considered that I had to all intents and purposes completed my
book. My first proof bears date October 13, 1877.

At this time I had not been able to find that anything like what I
was advancing had been said already. I asked many friends, but not
one of them knew of anything more than I did; to them, as to me, it
seemed an idea so new as to be almost preposterous; but knowing how
things turn up after one has written, of the existence of which one
had not known before, I was particularly careful to guard against
being supposed to claim originality. I neither claimed it nor wished
for it; for if a theory has any truth in it, it is almost sure to
occur to several people much about the same time, and a reasonable
person will look upon his work with great suspicion unless he can
confirm it with the support of others who have gone before him.
Still I knew of nothing in the least resembling it, and was so afraid
of what I was doing, that though I could see no flaw in the argument,
nor any loophole for escape from the conclusion it led to, yet I did
not dare to put it forward with the seriousness and sobriety with
which I should have treated the subject if I had not been in
continual fear of a mine being sprung upon me from some unexpected
quarter. I am exceedingly glad now that I knew nothing of Professor
Hering's lecture, for it is much better that two people should think
a thing out as far as they can independently before they become aware
of each other's works but if I had seen it, I should either, as is
most likely, not have written at all, or I should have pitched my
book in another key.

Among the additions I intended making while the book was in the
press, was a chapter on Mr. Darwin's provisional theory of