474 LAWS OF MULTIPLICATION. 



Each increment of evolution entails a decrement of r^ 

 production that is not accurately proportionate, but somewhat 

 less than proportionate. The gain in the one direction is not 

 wholly canceled by a loss in the other direction, but only 

 partially canceled : leaving a margin of profit to the species. 

 Though augmented power of self-maintenance habitually 

 necessitates diminished power of race- propagation, yet the 

 product of the two factors is greater than before ; so that the 

 forces preservative of race become, thereafter, in excess of the 

 forces destructive of race, and the race spreads. We shall 

 soon see why this happens. 



Each advance in evolution implies an economy. That any 

 increase in bulk, or structure, or activity, may become esta 

 blished, the life of the organism must be to some extent 

 facilitated by the change the cost of self-support must be, 

 on the average, reduced. If the greater complexity, or the 

 larger size, or the more agile movement, entails on the in 

 dividual an outlay that is not repaid in food more-easily 

 obtained, or danger more-easily escaped ; then the individual 

 will be at a relative disadvantage, and its diminished posterity 

 will disappear. If the extra outlay is but just made good 

 by the extra advantage, the modified individual will not sur 

 vive longer, or leave more descendants, than the unmodified 

 individuals. Consequently, it is only when the expense of 

 greater individuation is out-balanced by a subsequent saving, 

 that it can tend to subserve the preservation of the indi 

 vidual ; or, by implication, the preservation of the race 

 The vital capital invested in the alteration must bring 

 a more than equivalent return. A few instances 



will show that, whether the change results from direct 

 equilibration or from indirect equilibration, this must happen. 

 Suppose a creature takes to performing some act in an un 

 usual way leaps where ordinarily its kindred crawl, elude? 

 pursuit by diving instead of, like others of its kind, by swim 

 ming along the surface, escapes by doubling instead of by sheet 

 speed. Clearly, perseverance in the modified habit will, other 



