392 GROWTH OF THE 'ORIGIN.' [1845. 



C. Darwin to L. Jenyns i^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 (/. ^., 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. 



