GERMINAL SELECTION. 13 



the great explanatory principles by which we seek 

 to approach nearer to the secrets of nature. 



I am not of that opinion. I see in the growth of 

 doubts regarding the principle of selection and in 

 the pronounced and frequently bitter opposition which 

 it encounters, a transient depression only of the wave 

 of opinion, in which every scientific theory must de- 

 scend after having been exalted, here perhaps with 

 undue swiftness, to the highest pitch of recognition. 

 It is the natural reaction from its overestimation, 

 which is now followed by an equally exaggerated 

 underestimation. The principle of selection was not 

 overrated in the sense of ascribing to it too much 

 explanatory efficacy, or of extending too far its sphere 

 of operation, but in the sense that naturalists imag- 

 ined that they perfectly understood its ways of work- 

 ing and had a distinct comprehension of its factors, 

 which was not so. On the contrary, the deeper they 

 penetrated into its workings the clearer it appeared 

 that something was lacking, that the action of the 

 principle, though upon the whole clear and representa- 

 ble, yet when carefully looked into encountered numer- 

 ous difficulties, which were formidable, for the reason 

 that we were unsuccessful in tracing out the actual 

 details of the individual process, and, therefore, in 

 iixing the phenomenon as it actually occurred. We 

 can state in no single case how great a variation must 

 be to have selective value, nor how frequently it must 

 occur to acquire stability. We do not know when 

 and whether a desired useful variation really occurs, 

 nor on what its appearance depends; and we have no 

 means of ascertaining the space of time required for 

 the fulfilment of the selective processes of nature, and 

 hence cannot calculate the exact number of such proc- 



