30 SCIENCE FROM AN EASY CHAIR 



mental breeding in all kinds of living things by hundreds 

 of careful observers who have published the records of 

 their studies, we come to the step where Darwin makes 

 use of supposition or hypothesis. The question is, " Does 

 the one which, out of the thousands of slightly different 

 varieties, survives do so by haphazard ? or is there a neces- 

 sarily acting state of things which selects that one special 

 variety for survival ? " Gardeners and breeders of pigeons, 

 dogs, and cattle deliberately select the variations which 

 they desire, breed from them, and so carry on by inherit- 

 ance the special variation whilst they ruthlessly destroy 

 or restrain from breeding the numerous other variations 

 in their " stock " which they do not desire. " If," said 

 Darwin, " there is any necessarily selective mechanism in 

 Nature which could act as the breeder does, new varieties 

 might be ' naturally ' selected, and changes of form and 

 appearance naturally established, which in the course of 

 long ages would amount to such marked differences as 

 separate what we call one species from another." He 

 showed that there is a natural mechanism of the required 

 kind. "Since," he says, "the competition among the 

 members of any one kind or species for a place in life is 

 so very severe, and the hostile circumstances so varied, 

 and since all the competing offspring differ by ' variation ' 

 ever so little from one another, those varieties which are 

 better suited in even the smallest degree to hold their own 

 not merely in fighting with the others, but in withstanding 

 injurious influences, in escaping enemies, and in procuring 

 food, will be the ones which will survive, when a large 

 number of cases, many thousands, extending over a large 

 area and many years, are considered. Those which are 

 ' best fitted ' to get through the exceedingly numerous 

 dangers and difficulties of life will be the survivors." 

 Hence we get the survival of the fit the fit variations 

 by natural selection in the struggle for life. This, it 



