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 IJ, sec. I, 8, (15).] 
I also referred to the codperation 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 inzteal 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 150 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. 
