64 
C. L. Herrick 
reflect the fundamental law of motion of the species. Such are 
sexual elements. 
The great difficulty which has hitherto existed in construing 
natural selection has been the necessity of discovering some cause 
for variation. According to a dynamic hypothesis the core of 
energy constitutes a nucleus of spontaneity or unconditioned 
activity. The form of expression of this activity will be deter- 
mined in part by the structure’’ of the organism and this is 
dependent on its phylogeny, and in part by the extraneous 
impressions (environment). Unconditioned spontaneity has in 
the course of phylogeny become conditioned by its own past as 
well as the present of its environment; yet there is the element 
of spontaneity, and what is to be explained is not why it takes 
such or such a form or direction but why it does not take any of 
all other directions. The original unconditioned spontaneity 
was, then, a tendency to express itself in all ways or, in other 
words, infinite variability. This variability is no longer infinite 
in so far as the results of previous activity have precluded many 
forms of expression. The mathematical expression for the activity 
of any organism is composed of a vast number of factors mostly 
too complex for our analysis. Heredity is a comprehensive term 
for those factors connected with past activities which have modi- 
fied the figure of present activity. If we could comprehend the 
expression for the existing activities in any organism we might hope 
to predict the range of its variability and the effect of changes of 
environment on such variability, or, in other words, the actual 
variation. 
In attempting to understand the effect of selection one must 
have regard: (I) to the status presens of the organic activity and 
its cyclical alterations ; (2) to the balance of element with element 
or part with part which will be disturbed when any new force 
enters the environment; (3) the direct tendency of that force. 
For example, a condition of darkness may directly interrupt 
certain visual processes and alter the circulatory and nervous 
equilibrium, but indirectly it may cause compensatory changes 
in nutrition of other organs ; or the development of antlers in one 
part may be correlated with changes in other parts of the integu- 
ment quite independent of the necessary changes in muscular 
control due to the added weight. In such matters as the forma- 
tion of color-patterns this law may be very important. 
