noured me by thinking it advisable to publish, with Mr. Wallace's
excellent memoir, some brief extracts from my manuscripts.

This Abstract, which I now publish, must necessarily be imperfect. I cannot
here give references and authorities for my several statements; and I must
trust to the reader reposing some confidence in my accuracy. No doubt
errors will have crept in, though I hope I have always been cautious in
trusting to good authorities alone. I can here give only the general
conclusions at which I have arrived, with a few facts in illustration, but
which, I hope, in most cases will suffice. No one can feel more sensible
than I do of the necessity of hereafter publishing in detail all the facts,
with references, on which my conclusions have been grounded; and I hope in
a future work to do this. For I am well aware that scarcely a single point
is discussed in this volume on which facts cannot be adduced, often
apparently leading to conclusions directly opposite to those at which I
have arrived. A fair result can be obtained only by fully stating and
balancing the facts and arguments on both sides of each question; and this
cannot possibly be here done.

I much regret that want of space prevents my having the satisfaction of
acknowledging the generous assistance which I have received from very many
naturalists, some of them personally unknown to me. I cannot, however, {3}
let this opportunity pass without expressing my deep obligations to Dr.
Hooker, who for the last fifteen years has aided me in every possible way
by his large stores of knowledge and his excellent judgment.

In considering the Origin of Species, it is quite conceivable that a
naturalist, reflecting on the mutual affinities of organic beings, on their
embryological relations, their geographical distribution, geological
succession, and other such facts, might come to the conclusion that each
species had not been independently created, but had descended, like
varieties, from other species. Nevertheless, such a conclusion, even if
well founded, would be unsatisfactory, until it could be shown how the
innumerable species inhabiting this world have been modified, so as to
acquire that perfection of structure and coadaptation which most justly
excites our admiration. Naturalists continually refer to external
conditions, such as climate, food, &c., as the only possible cause of
variation. In one very limited sense, as we shall hereafter see, this may
be