FECUNDAL SELECTION. 91 



the same as in the body of the original species, the average form of the 

 isolated group will in a few generations become different from the 

 average form in the original stock, even though the environment sur- 

 rounding each is the same. I also noted that "the chief check to this 

 law of cumulative fertility is found in the antagonistic (that is, rival, 

 and sometimes severely competing) law of cumulative adaptation 

 through adaptational selection." [See Appendix II, sec. I, 8, (15).] 

 I also referred to the cooperation of the two factors in the fol- 

 lowing words: 



The combined action of these two laws results in the triumphant development 

 of the most fertile of the best fitted or the best fitted of the most fertile. Another 

 result from their combined action is that in species well adjusted to the environ- 

 ment 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 adap- 

 tation in the average form of the species or race is a strongly conservative principle, 

 tending to prevent the over-rapid transformation of the race or species. 



In the more exact definition of fecundal selection given above I 

 point out that the chief condition restraining the action of this prin- 

 ciple is found in the average power of parents for parental nourishing 

 and postnatal rearing and training of offspring. The initial fertility 

 depends on the abundance of the ova and the proportionate correla- 

 tion between the numbers of the ova and the fertilizing cells ; while 

 the final fertility must depend, not only on these correlations produc- 

 ing initial fertility, but on that form of filio-parental selection which 

 secures the correlation between initial fertility and the power of the 

 parents to nourish and develop the ova after fertilization and to rear 

 and train the young till they are capable of independent life. If the 

 degree of initial fertility overtaxes the power for producing or rearing 

 offspring, the final fertility may fall far below the need for survival, 

 while if the young could only reach maturity in good condition the 

 fertility would be far above the need. 



Certain domestic breeds show clearly the nature of the disaster that 

 would come to any species under natural conditions if filio-parental 

 selection were so far suspended as to break down the coordination 

 between the initial fertility and the power of the parents to bring the 

 young to maturity. The Leghorn hen lays from 1 50 to 200 eggs in a 

 year, and seldom cares to set. It is evident that such a race would 

 run great risk of extinction if separated from the care of those who are 

 in the habit of providing methods for the hatching and rearing of the 

 young. Even if some of the race should regain the instincts required 

 for hatching out and rearing their young, how impossible would be the 

 task of hatching and raising twelve or thirteen full broods in a year. 



