MODERN EVOLUTION. 



133 



monograph on earthworms. With bad health, ap- 

 parently due to gouty tendencies aggravated by 

 chronic sea-sickness during his voyage; with nights 

 that never gave unbroken sleep; and days that were 

 never passed without prostrating pain; he might 

 well have felt justified in doing nothing whatever. 

 But he was saved from the accursed monotony of a 

 wealthy invalid's life by his insatiate delight in 

 searching for that solution of the problem of the 

 mutability of species which time would not fail to 

 bring. In this, he tells us, he forgot his " daily dis- 

 comfort," and thus was delivered from morbid intro- 

 spection. 



Darwin worked at his rough notes on the varia- 

 tion of animals and plants under domestication, add- 

 ing facts collected by " printed enquiries, by con- 

 versations with skilful breeders and gardeners, and 

 by extensive reading," gleams of light coming till 

 he says that he is " almost convinced that species 

 are not (it is like confessing a murder) immutable." 

 But he was still groping in the dark as to the appli- 

 cation of selection to wild plants and animals, until, 

 as remarked above, the chance reading of Malthus 

 suggested a working theory. A brief sketch of this 

 theory, written out in pencil in 1842, was elaborated 

 in 1844 into an essay of two hundred and thirty 

 pages. The importance attached to this was shown 

 in a letter which Darwin then addressed to his wife, 

 charging her, in the event of his death, to apply 

 400 to the expense of publication. He also named 



