Oh. X.] 1843—1858. 175 



require, in my case, some leisure and energy, [of] both of which 

 ingredients I have had none to spare, as writing my Geology 

 thoroughly expends both. I had always thought that I would 

 keep a journal and record everything, but in the way I now 

 live I find I observe nothing to record. Looking after my 

 garden and trees, and occasionally a very little walk in an idle 

 frame of my mind, fill up every afternoon in the same 

 manner. I am surprised that with all your parish affairs, you 

 have had time to do all that which you have done. I shall be 

 very glad to see your little work * (and proud should I have 

 been if I could have added a single fact to it;. My work on 

 the species question has impressed me very forcibly with the 

 importance of all such works as your intended one, containing 

 what people are pleased generally to call trifling facts. These 

 are the facts which make one understand the working or 

 economy of nature. There is one subject, on which I am very 

 curious, and which perhaps you may throw some light on, if 

 you have ever thought on it ; namely, what are the checks and 

 what the periods of life — by which the increase of any given 

 species is limited. Just calculate the increase of any bird, if 

 you assume that only half the young are reared, and these 

 breed : within the natural (i.e. if free from accidents) life of the 

 paronts the number of individuals will become enormous, and I 

 have been much surprised to think how great destruction must 

 annually or occasionally be falling on every species, yet the 

 means and period of such destruction are scarcely perceived by us. 

 I have continued steadily reading and collecting facts on 

 variation of domestic animals and plants, and on the question 

 of what are species. I have a grand body of facts, and I 

 think I can draw some sound conclusions. The general con- 

 clusions at which I have slowly been driven from a directly 

 opposite conviction, is that species are mutable, and that allied 

 species are co-descendants from common stocks. I know how 

 much I open myself to reproach for such a conclusion, but I 

 havo at least honestly and deliberately come to it. I shall 

 not publish on this subject for several years. 



C. Darwin to L. Jenyns.] Down [1845 ?]. 



With respect to my far distant work on species, I must have 

 expressed myself with singular inaccuracy if I led you to 



* Mr. Jenyns' Observations in Natural History. It is prefaced by an 

 Introduction on " Habits of observing as connected with the study of 

 Natural History," and followed by a " Calendar of Periodic Phenomena 

 in Natural History," with " Remarks on the importance of such Registers." 



t Rev. L. Blomefield. 



