C. Lloyd Morgan 345 



tions of the bodily tissues, due to innate plasticity and variations 

 of germinal origin in similar adaptive directions, we may revert 

 to the pendulum analogy. Assuming that variations do tend 

 to occur in a great number of divergent directions, we may liken 

 each to a pendulum which tends to swing, — nay, which is swing- 

 ing through a small arc. The organism, so far as variation is 

 concerned, is a complex aggregate of such pendulums. Sup- 

 pose, then, that it has reached congenital harmony with its 

 environment. The pendulums are all swinging through the 

 small arcs implied by the slight variations which occur even 

 among the offspring of the same parents. No pendulum can 

 materially increase its swing ; for since the organism has reached 

 congenital harmony with its environment, any marked variation 

 wall be out of harmony, and the individual in which it occurs 

 will be eliminated. Natural selection then will insure the 

 damping down of the swing of all the pendulums in compara- 

 tively narrow limits. 



" But now suppose that the environment somewhat rapidly 

 changes. Congenital variations of germinal origin will not be 

 equal to the occasion. The swing of the pendulums concerned 

 cannot be rapidly augmented. Here individual plasticity steps 

 in to save some members of the race from extinction. They 

 adapt themselves to the changed conditions through a modifica- 

 tion of the bodily tissues. If no members of the race have 

 sufficient innate plasticity to effect this accommodation, that race 

 will become extinct, as has indeed occurred again and again in 

 the course of geological history. The rigid races have suc- 

 cumbed ; the plastic races have survived. Let us grant, then, 

 that certain organisms accommodate themselves to the new con- 

 ditions by plastic modifications of the bodily tissues — say by the 

 adaptive strengthening of some bony structure. What is the 

 effect on congenital variations ? Whereas all the other pendu- 

 lums are still damped down by natural selection as before, the 

 oscillation of the pendulum which represents variation in this 

 bony structure is no longer checked. It is free to swing as 

 much as it can. Congenital variations in the same direction as 

 the adaptive modification will be so much to the good of the 



