XXI 
MENTAL FACTORS IN EVOLUTION 
By C. Luoyp Morgan, LL.D., F.R.S. 
In developing his conception of organic evolution Charles Darwin 
was of necessity brought into contact with some of the problems of 
mental evolution. In The Origin of Species he devoted a chapter 
to “the diversities of instinct and of the other mental faculties in 
animals of the same class!” When he passed to the detailed con- 
sideration of The Descent of Man, it was part of his object to show 
“that there is no fundamental difference between man and the higher 
mammals in their mental faculties” “If no organic being excepting 
man,” he said, “had possessed any mental power, or if his powers had 
been of a wholly different nature from those of the lower animals, 
then we should never have been able to convince ourselves that our 
high faculties had been gradually developed®.” In his discussion of 
The Expression of the Emotions it was important for his purpose 
“fully to recognise that actions readily become associated with other 
actions and with various states of the mind‘.” His hypothesis of 
sexual selection is largely dependent upon the exercise of choice on 
the part of the female and her preference for “not only the more 
attractive but at the same time the more vigorous and victorious 
males®.” Mental processes and physiological processes were for 
Darwin closely correlated; and he accepted the conclusion “that 
the nervous system not only regulates most of the existing functions 
of the body, but has indirectly influenced the progressive develop- 
ment of various bodily structures and of certain mental qualities®.” 
Throughout his treatment, mental evolution was for Darwin in- 
cidental to and contributory to organic evolution. For specialised 
research in comparative and genetic psychology, as an independent 
field of investigation, he had neither the time nor the requisite 
training. None the less his writings and the spirit of his work have 
1 Origin of Species (6th edit.), p. 205. 
* Descent of Man (2nd edit. 1888), Vol. 1. p. 99; Popular edit. p. 99. 3 Ibid. p. 99. 
* The Expression of the Emotions (2nd edit.), p. 32. 
5 Descent of Man, Vol. 1. p. 435. § Ibid. pp. 487, 438. 
