326 THE INDUCTIONS OF BIOLOGY. 



positive impediments to its growth which competing wild 

 plants before offered. An animal taken from woods or plains, 

 where it lived on wild food of its own procuring, and placed 

 ■under restraint while artificially supplied with food not quite 

 like what it had before, is an animal subject to new outer 

 actions to which its inner actions must be adjusted. From 

 the general law of equilibration we found it to follow that 

 "the maintenance of such a moving equilibrium" as an 

 organism displays, " requires the habitual genesis of internal 

 forces corresponding in number, directions, and amounts, to 

 the external incident forces — as many inner functions, single 

 or combined, as there are single or combined outer actions to 

 be met " {First Principles, § 173) ; and more recently (§27), 

 we have seen that Life itself is " the definite combination of 

 heterogeneous changes, both simultaneous and successive, in 

 correspondence with external co-existences and sequences." 

 Necessarily, therefore, an organism exposed to a permanent 

 change in the arrangement of outer forces must undergo a 

 permanent change in the arrangement of inner forces. The 

 old equilibrium has been destroyed; and a new equilibrium 

 must be established. There must be functional perturbations, 

 ending in a re-adjusted balance of functions. 



If, then, change of conditions is the only known cause by 

 which the original homogeneity of a species is destroyed; 

 and if change of conditions can affect an organism only by 

 altering its functions; it follows that alteration of func- 

 tions is the only known internal cause to which the com- 

 mencement of variation can be ascribed. That such minor 

 functional changes as parents undergo from year to year are 

 influential on the offspring, we have seen is proved by the 

 greater unlikeness that exists between children born to the 

 same parents at different times, than exists between twins. 

 And here we seem forced to conclude that the larger func- 

 tional variations produced by greater external changes, are 

 the initiators of those structural variations which, when 

 once commenced in a species, lead by their combinations and 



