INTENSIVE SEGHIEQATIOK. 345 



possessed by tlie same forms of variation in separate sections ot the 

 species. — Eelative Fecundity is propagation according to degrees 

 of fertility. As it involves not only the superior propagation o£ 

 tlie more fertile, but the inferior propagation of the less fertile 

 and the non-propagation of the least fertile, it may be de- 

 scribed as the exclusive propagation of the more fertile, through 

 the failure to propagate of the less fertile. It would avail 

 nothing in determining the form that is to prevail in succeeding 

 generations if it did not in some degree preclude the crossing of 

 the less fertile with the more ; but, as it is evident that, so long 

 as increased fertility is not a disadvantage, the more fertile halt 

 of the species will leave a larger number of oflspriug than the 

 less iertile half, it follows that when the offspring have come to 

 maturity a larger portion of the fertile will consort with the 

 fertile than in the previous generation, and so the fertdity of the 

 following generation will be still further increased. The chief 

 check to this law of Omnulative Fertility is found in the antago- 

 nistic law of Cumulative Adaptation through Adaptational Selec- 

 tion. The combined action of these two laws results in the 

 triumphant development of tbe most fertile of the best fitted, or 

 the best fitted of the most fertile. 



Another result from the combined action of these two laws is 

 that in species that are well adjusted to the environment the 

 typical, that is the average, form of the species is not only the 

 best adapted, but it is the most fertile ; and this correlation 

 between fertility and adaptation in the average form of the species 

 or race is a strongly conservative principle, tending to prevent 

 the rapid transformation of the race or species. Griants, dwarfs, 

 and extreme departures from the type of other kinds are more 

 likely to be sterile than the typical form of the species; and 

 therefore if, through change in the environment or in the social 

 conditions, some extreme form has an advaiitage in gaining sub- 

 sistence, it will usually fail of propagating its kind with the rela- 

 tive rapidity of the less-favom-ed average form. This is at present 

 true of highly intellectiial variations of civilized man. Those of 

 moderate capacities are more ]n-olific, and aecordingly persist, 

 though less successful in other respects than the intellectual. 

 But so long as the most successful individuals are those surpassing 

 the average in intellectual endowment, so long will the average 

 endowment be more or less steadily advancing ; for, of intellectual 

 families, those that are fairly fertile will leave more impress on 



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