32 SCIENCE FROM AN EASY CHAIR 



important to turn the scale in favour of survival or non- 

 survival. It is not easy for a man who is not a determined 

 naturalist, constantly observing the ways of wild living 

 things, to appreciate the evidence as to the efficacy of 

 small variations, even were I able here to submit it to 

 him. It is to be found in the published works of an army 

 of investigators. In any case it is granted that effective 

 variations whether small or great occur in nature, and 

 that natural selection favours and perpetuates the new 

 and fitter variety to the exclusion of the less fit. 



The real difficulty to most people comes in the 

 supposition next made by Mr. Darwin namely, that this 

 slow process of change by natural selection of favoured 

 variations and their transmission and perpetuation by 

 inheritance is sufficient to effect by its continued opera- 

 tion through enormous ages of time the conversion of a 

 race of ancestral three-toed zebras into the one-toed horse 

 of to-day ; before that, of five-toed beasts into three-toed ; 

 at an earlier stage of fishlike creatures into four-footed 

 land animals, and so on. You have to picture the whole 

 series of animals and of plants which are now or ever 

 have been, as two gigantic family trees or pedigrees, 

 meeting in common ancestors of the simplest grade of 

 microscopic life. All the diverging branches and twigs of 

 these great " family trees " have been determined by the 

 adaptation of living form to the endlessly varied condi- 

 tions of life on this planet, by the natural selection or 

 survival of variations and the transmission and accumula- 

 tion of those variations from parent to offspring. This is 

 a tremendous demand on the imagination. It is, however, 

 not a difficult one to concede, when one is acquainted with 

 the facts and conclusions of geology. The history of the 

 crust of the earth was explained twenty years before 

 the date of Darwin's theory by Charles Lyell as due to the 

 continued action through immense periods of time of the 



