DARWIN AND THE ORIGIN OF SPECIES 231 



there be 7,002 A's to start, the odds would be laid on the A's. 

 True, they stand a greater chance of being killed ; but then 

 they can better afford to be killed. The grain will only turn 

 the scales when these are very nicely balanced, and an advan- 

 tage in numbers counts for weight, even as an advantage in 

 structure. As the numbers of the favoured variety diminish, so 

 must its relative advantage increase, if the chance of its exist- 

 ence is to surpass the chance of its extinction, until hardly any 

 conceivable advantage would enable the descendants of a single 

 pair to exterminate the descendants of many thousands if they 

 and their descendants are supposed to breed freely with the 

 inferior variety, and so gradually lose their ascendency. If it 

 is impossible that any sport or accidental variation in a single 

 individual, however favourable to life, should be preserved and 

 transmitted by natural selection, still less can slight and imper- 

 ceptible variations, occurring in single individuals, be garnered 

 up and transmitted to continually increasing numbers ; for if a 

 very highly favoured white cannot blanch a nation of negroes, it 

 will hardly be contended that a comparatively very dull mulatto 

 has a good chance of producing a tawny tribe ; the idea, which 

 seems almost absurd when presented in connection with a practical 

 case, rests on a fallacy of exceedingly common occurrence in 

 mechanics and physics generally. When a man shows that a 

 tendency to produce a given effect exists, he often thinks he has 

 proved that the effect must follow. He does not take into 

 account the opposing tendencies, much less does he measure the 

 various forces, with a view to calculate the result. For instance, 

 there is a tendency on the part of a submarine cable to assume 

 a catenary curve, and very high authorities once said it would ; 

 but, in fact, forces neglected by them utterly alter the curve 

 from the catenary. There is a tendency on the part of the same 

 cables, as usually made, to untwist entirely ; luckily there are 

 opposing forces, and they untwist very little. These cases will 

 hardly seem obvious ; but what should we say to a man who 

 asserted that the centrifugal tendency of the earth must send it 

 off in a tangent ? One tendency is balanced or outbalanced by 

 others ; the advantage of structure possessed by an isolated 

 specimen is enormously outbalanced by the advantage of numbers 

 possessed by the others. 



