594 TRANSACTIONS OF SECTION H. 
In coinparison with the Apes, Man has an enormously enhanced faculty of 
profiting by experience, and of controlling the impulse to respond to every 
sensory stimulus in his environment by recalling the consequences of such 
responses on previous occasions. We may correlate these contrasts in behaviour 
with the striking differences in the cerebral cortex. In the Ape the activity of 
the greater part of the neopallium is to a large extent controlled by impressions 
streaming into its various parts from one or other of the sense-organs or other 
sensitive structures in the body. In the course of evolution of the human brain 
there is added to this cortex of Man’s Simian progenitor a mass of tissue, roughly, 
about five hundred cubic centimetres, bigger than the whole of the Gorilla’s 
brain; and as the sensory areas of the human brain are practically equal to 
those of the Gorilla, all this enormous increase goes to swell the dimensions 
of those parts of the cortex which do not receive sensory impressions directly. 
These neopallial areas are at least six times as large in the human brain as they 
are in the Gorilla’s. ‘lo put these facts into a slightly different form, in the 
Simian brain the sensory areas predominate, and the behaviour of the animal is 
to be looked upon as the response to the immediate sensory impressions of the 
moment : in the human brain the great association areas have grown far beyond 
the dimensions of the sensory areas, and experience, the effects of education, 
and knowledge assume the dominant rdle in influencing conduct. 
In the series of Primates it is fotnd that the size of the cortical area con- 
trolling skilled movements increases as we ascend the scale, and the variety, 
complexity, and skilled nature of the movements become markedly increased. 
The extent to which the Anthropoid Apes can be trained to remember and per- 
form the most complex actions must be familiar to everyone who has visited 
the modern ‘ music-hall’ or travelling menagerie. % 
Thus it happens when the brain reaches the stage in its evolution to impel its 
possessor to attempt complex purposive acts directed toward the accomplishment 
of some intelligent aim, the hand and arm are not only ready and free from 
the duty of progression, but they already have attained in great measure the 
skill and the cunning to perform what the intelligent will requires of them. 
What more favourable conditions could be imagined than these for the forces 
of natural selection to seize hold of, to fix and establish more definitely the erect 
attitude, to make the hand a more delicate and exact instrument capable of per- 
forming infinitely more complex and varied skilled actions, to make the leg a 
more efficient support, and thereby simultaneously to give still more freedom to 
the all-important hand, while the growing brain is all the time becoming more 
richly endowed with the potentialities of the conscious memory, reciprocally 
stimulating and being stimulated by the motor centres, which, by directing the 
performance of new manceuvres, add to the storehouse of consciousness new 
elements of experience of cause and effect? 
The erect attitude, infinitely more ancient than Man himself, is not the real 
cause of man’s emergence from the Simian stage; but it is one of the factors made 
use of by the expanding brain as a prop still further to extend its growing 
dominion, and by fixing and establishing in a more decided way this erectness it 
liberates the hand to become the chief instrument of Man’s further progress. 
In learning to execute movements of a degree of delicacy and precision to 
which no Ape could ever attain, and which the primitive Ape-man could only 
attempt once his arm was completely emancipated from the necessity of being 
an instrument of progression, that cortical area which seemed to serve for the 
phenomena of attention became enhanced in importance. Hence the prefrontal 
region, where the activities of the cortex as a whole are, as it were, focussed 
and regulated, began to grow until eventually it became the most distinctive 
characteristic of the human brain, gradually filling out the front of the cranium 
and producing the distinctively human forehead. In the diminutive prefrontal 
area of Pithecanthropus,*' and, to a less marked degree, Neanderthal man,**, we 
see illustrations of lower human types, bearing the impress of their lowly state 
in receding foreheads and great brow-ridges. However large the brain may be 
41 Eug. Dubois, ‘Remarks upon the Brain-cast of Pithecanthropus,’ Proc. 
Fourth Internat. Cong. Zool., August 1898, published Camb., 1899, p. 81. 
* Boule and Anthony, ‘ L’encéphale de l'homme fossile de la Chapelle-aux- 
Saints,’ L’Anthropologie, tome xxii., No, 2, 1911, p. 50, 
