392 GROWTH OF THE 'ORIGIN.' [1845 



C. Darwin to L. Jenyns {Blome field}. 



Down, Oct. I2th, [1845]. 



MY DEAR JENYNS, Thanks for your note. I am sorry to 

 say I have not even the tail-end of a fact in English Zoology 

 to communicate. I have found that even trifling observations 

 require, in my case, some leisure and energy, 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 mind, fills up every afternoon in the same man- 

 ner. 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, contain- 

 ing 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 acci- 

 dents) life of the parents the number of individuals will be- 

 come enormous, and I have been much surprised to think 

 how great destruction must annually or occasionally be falling 



* 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." 

 My father seems to be alluding to this Register in the P.S. to the letter 

 dated Oct. 17, 1846. 



