VARIATIONS. 225 



will, on the whole, be intermediate between the 

 average individual and the sport. The odds in 

 favor of one of this generation will be, say, one and 

 a half to one, as compared with the average indi- 

 vidual ; the odds in their favor will be less than that 

 of their parent. But, owing to their greater number, 

 the chances are that about one and a half would 

 survive. Unless these breed together, a most im- 

 probable event, their progeny would again approach 

 the average individual. There would be one hun- 

 dred and fifty of them, and their superiority would 

 be, say, in the ratio of one and a quarter to one." 

 In the next generation the superiority by further 

 crossing would be even less ; and thus the variation 

 which appears so strong in the first individual will 

 dwindle away, and in a few generations practically 

 disappear. While natural selection would have a ten- 

 dency to select the favored individual, the necessity 

 of cross-breeding would have a much more powerful 

 effect in causing the variation to disappear. 



To this difficulty no one has suggested any suffi- 

 cient answer. Darwin acknowledged its full force, 

 and admitted that very rarely is it possible for a 

 single variation to be preserved. He thinks, how- 

 ever, that if a third, a fifth, or even a tenth part of 

 the individuals be simultaneously modified by some 

 cause (such as similar conditions affecting different 

 individuals in a similar way), and if the variation 

 should be of a beneficial nature, the original form 

 would soon be supplanted by the modified form 

 through the survival of the fittest. This will prob- 

 ably be admitted by all, but it is evident that with 



