196 
REV. J. T. GULICK ON DIVERGENT EVOLUTION 
complex environment ; it is therefore with special pleasure that 
I observe that a law of very similar import may be derived by a 
wholly different method from the general laws of action and 
reaction in the physical world. It should, however, be noticed 
that in the brief references made to the subject in Spencer’s 
£ Principles of Biology ’ * it is assumed that “ Increasingly- 
definite distinctions among variations are produced, wherever 
there occur definitely-distinguished sets of conditions to which 
the varieties are respectively subject,” and. only where these 
occur ; for “ Vital actions remain constant so long as the external 
actions to which they correspond remain constant ; ” and no 
reference is anywhere made to the principle that whatever causes 
sexual separation between dissimilar members of one family, race, 
or species tends not only to perpetuate, but to increase their 
dissimilarity in the succeeding generations. The view maintained 
in the following paper is, I believe, in better accord with the 
fundamental principle that “ Unlike units of an aggregate are 
sorted into their kinds and parted when uniformly subject to the 
same incident forces,” + as is also the teaching of Spencer’s 
1 Principles of Biology ’ in one passage ; for I have recently dis- 
covered that in a single paragraph of this work it is maintained 
that, while exposed to the same external conditions, the members 
of the same species may be increasingly differentiated, “ until at 
length the divergence of constitutions and modes of life become 
great enough to lead to segregation of the varieties.” + If 
the segregation had been introduced as a necessary condition 
without which the divergence of families and races could not 
take place, the position taken in this paragraph would have been 
essentially the same as the one I have adopted. In the next 
section, however, he abandons the position, using the following 
words : — “ Through the process of differentiation and integration 
which of necessity brings together, or keeps together, like indi- 
viduals, and separates unlike ones from them, there must never- 
theless he maintained a tolerably uniform species , so long as there 
continues a tolerably uniform set of conditions in ivhich it may 
exist." [The italics are mine.] 
I trust my endeavour to contribute something toward the 
development of the theory of divergent evolution will not be 
* Compare §§ 91, 156, 169, 170. 
t See Spencer’s ‘ First Principles,’ § 166, near the end ; also a fuller state- 
ment in § 169. J See § 90. 
