2 INTRODUCTION. 



who both knew of my work — the latter having read my 

 sketch of 1844 — honored 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 

 may have crept in, though I hope I have always been cau- 

 tious 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 appar- 

 ently 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 is here impossible. 



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, 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 conceiv- 

 able that a naturalist, reflecting on the mutual affinities of 

 organic beings, on their embryological relations, their geo- 

 graphical distribution, geological succession, and other such 

 facts, might come to the conclusion that 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 justly excites our admira- 

 tion. Naturalists continually refer to external conditions, 

 such as climate, food, etc., as the only possible cause of 

 variation. In one limited sense, as we shall hereafter see, 



