that more time has elapsed, I have endeavoured to profit by the fiery
ordeal through which the book has passed, and have taken advantage of all
the criticisms which seem to me sound. I am also greatly indebted to a
large number of correspondents for the communication of a surprising number
of new facts and remarks. These have been so numerous, that I have been
able to use only the more important ones; and of these, as well as of the
more important corrections, I will append a list. Some new illustrations
have been introduced, and four of the old drawings have been replaced by
better ones, done from life by Mr. T.W. Wood. I must especially call
attention to some observations which I owe to the kindness of Prof. Huxley
(given as a supplement at the end of Part I.), on the nature of the
differences between the brains of man and the higher apes. I have been
particularly glad to give these observations, because during the last few
years several memoirs on the subject have appeared on the Continent, and
their importance has been, in some cases, greatly exaggerated by popular
writers.

I may take this opportunity of remarking that my critics frequently assume
that I attribute all changes of corporeal structure and mental power
exclusively to the natural selection of such variations as are often called
spontaneous; whereas, even in the first edition of the 'Origin of Species,'
I distinctly stated that great weight must be attributed to the inherited
effects of use and disuse, with respect both to the body and mind. I also
attributed some amount of modification to the direct and prolonged action
of changed conditions of life. Some allowance, too, must be made for
occasional reversions of structure; nor must we forget what I have called
"correlated" growth, meaning, thereby, that various parts of the
organisation are in some unknown manner so connected, that when one part
varies, so do others; and if variations in the one are accumulated by
selection, other parts will be modified. Again, it has been said by