190 APPENDIX II—INTENSIVE SEGREGATION. 
of at least a portion of their ancestry, and the correlation of these 
endowments must have been produced through the action of other 
principles. 
The prevalence of males in times of pressure, with the prevalence of 
females in times of plenty, is regarded by Dr. W. K. Brooks, of Johns 
Hopkins University, as a characteristic established by natural selec- 
tion, by which the organism acquires variability or fixity of type 
according as either character is most needed; for according to his 
observations the males represent the former and the females the latter 
element. ‘There can be no doubt that in many species the males are 
more variable than the females, and that in some of the same species 
the proportion of males increases with the degree of adversity; but 
this does not seem to be sufficient ground for maintaining that the 
increase in the proportion of males will increase the variability of 
the offspring. Increase in the number or amount of the variable 
element does not necessarily involve increase in the variability of 
either element or in the offspring of both. I find need of additional 
factors in order to bring these facts into any relation to the increase 
of variability. Granting that the sperm-cell is the source of variation 
and the germ-cell the source of fixity, and that increased tendency 
to variation in the offspring will be secured by an increased range 
of variation in the sperm-cells, it does not follow that increase in 
the relative number of males will increase the range of variation in 
the sperm-cells, and, therefore, in the offspring. But if conflict in the 
environment and the winnowing process of natural selection falls 
most heavily upon the males, there must be some advantage in having 
their relative numbers increased in times of adversity; and if the 
exposure of parents to hardships increases the variability of either 
male or female offspring, and especially if it increases the variability 
of both, plasticity will be increased. 
Professor Cope’s ‘‘ Doctrine of the Unspecialized’”’ (Origin of the 
Fittest, pp. 232-235) rests on the fact that the most highly specialized 
types, as well as individuals, are most likely to be exterminated by 
extraordinary changes in the environment; and Mr. Hyatt’s ‘‘Tera- 
tology’’ (Proceedings American Association, vol. Xxx, pp. 349-360) 
teaches that types that are being slowly exterminated usually assume 
forms resembling those produced by old age and disease in the indi- 
vidual. These and other laws in the growth and decay of types 
and individuals are of great interest, as they afford organic condi- 
tions under which the factors of transformation must act. 
