1896.] A New Factor in Evolution. 543 
movement tends to discharge motor energy into the chan- 
nels as near as may be to those necessary for that move- 
ment” (ref. 3). By this organic concentration and excess of 
movement many combinations and variations are rendered 
possible, from which the advantageous and adaptive move- 
ments may be selected for their utility. These then give 
renewed pleasure, excite pleasurable associations, and again 
stimulate the attention, and by these influences the adaptive move- 
ments thus struck are selected and held as permanent acquisitions. 
This form of concentration of energy upon stimulated locali- 
ties, with the resulting renewal by movements of conditions 
that are pleasure-giving and beneficial, and the subsequent 
repetitions of the movements, is called the “ circular reaction.”* 
(ref. 1, 2). Itis the selective property which Romanes pointed 
out as characterizing and differentiating life. It characterizes 
the responses of the organism, however low in the scale, to all 
stimulations—even those of a mechanical and chemical (phy- 
sico-genic) nature. Pfeffer has shown such a determination of 
energy toward the parts stimulated even in plants. And in 
the higher animals it finds itself exactly reproduced in the 
nervous reaction seen in imitation and—through processes of 
association, substitution, ete.—in all the higher mental acts of 
intelligence and volition. These are developed phylogeneti- 
cally as variations whose direction is constantly determined, by 
this form of adaptation.in ontogenesis. If this be true—and the 
biological facts seem fully to confirm it—this is the adaptive 
process in all life, and this process is that with which the devel- 
opment of mental life has been associated. 
It follows, accordingly, that the three forms of ontogenetic 
adaptation distinguished above—physico-genetic, neuro-gene- 
tic, psycho-genetic—all involve the sort of response on the part 
of the organism seen in this circular reaction with excess dis- 
charge; and we reach one general law of ontogenetic adap- 
tation and of Organic Selection. “The accommodation of 
an organism to a new stimulation is secured—not by the selec- 
tion of this stimulation beforehand (nor of the necessary move- 
* With the opposite (withdrawing, depressive affects) in injurious and painful 
conditions. 
