596 TRANSACTIONS OF SECTION H. 
the forces of natural selection made one hand more apt to perform skilled move- 
ments than the other. Why precisely it was the right hand that was chosen in 
the majority of mankind we do not know, though scores of anatomists and 
others are ready with explanations. But probably some slight mechanical 
advantage in the circumstances of the limb, or perhaps even some factor affect- 
ing the motor area of the left side of the brain that controls its movements, may 
have inclined the balance in favour of the right arm; and the forces of heredity 
have continued to perpetuate a tendency long ago imprinted in Man’s structure 
when first he became human. 
The fact that a certain proportion of mankind is left-handed, and that such 
a tendency is transmitted to- some only of the descendants of a left-handed 
person, might perhaps suggest that one half of mankind was originally left- 
handed and the other right-handed, and that the former condition was recessive 
in the Mendelian sense, or that some infinitesimal advantage may have accrued to 
the right-handed part of the original community, which in time of stress spared 
them in preference to left-handed individuals; but the whole problem of why 
right-handedness should be rauch more common than left-handedness is still quite 
obscure. The superiority of one hand is as old as mankind, and is one of the 
factors incidental to the evolution of Man. 
It is easily comprehensible why one hand should become more expert than 
the other, as I have attempted to show; and the fact remains that it is the right 
hand, controlled by the left cerebral hemisphere, which is specially favoured in 
this respect. This heightened educability of the (left) motor centre (for the 
right hand) has an important influence upon the adjoining areas of the left motor 
cortex. When the Ape-Man attained a sufficient degree of intelligence to wish 
to communicate with his fellows other than by mere instinctive emotional cries 
and grimaces, such as all social groups of animals employ, the more cunning 
right hand would naturally play an important part in such gestures and signs; 
and, although the muscles of both sides of the face would be called into action 
in such movements of the features as were intended to convey information to 
another (and not merely to express the personal feelings of the individual), such 
bilateral movements would certainly be controlled by the left side of the brain, 
because it was already more highly educated. 
Up to this stage the means of communication with other individuals was 
practically confined to signs and gestures, controlled by the left brain of the 
signaller and appreciated by the visual apparatus of the receiver: and no doubt 
a special bond was established between the visual areas, in which the memories 
of such signs and their meanings were recorded, and the area in which the 
memories of the particular movements of arms and face were stored: and as 
the latter were controlled in the left hemisphere, the bond between the visuo- 
psychic and arm-head motor centres would be specially intimate in the left 
cerebral hemisphere. i 
The increased control acquired by the left motor centres (over the right hand 
and both sides of the face) also extended to the left centres that regulate the 
muscles of the tongue, palate, and larynx; and the skill that the primitive 
Ape-Man had acquired to perform delicately adjusted actions with the right hand 
and face naturally became extended to include these other muscles, the move- 
ments of which are regulated by the adjoining cortical area, and are also used 
to aid in expressing the ideas conveyed by the movements of the hand and face. 
Then he learned to make a much greater variety of sounds than he has inherited 
from his Gorilla-like and Gibbon-like ancestors. To the memories of the sounds 
of other animals and of the noises that occur in Nature, which had already 
become stored up in the sensorium of Apes, the primitive Ape-Man added a 
collection of records of the expressive sounds deliberately emitted by his fellows ; 
and in course of time the consciousness of these sounds was recorded, along with 
the memories of his gestures and grimaces, associating each with some meaning, 
which became a new way of communicating with his fellows. 
The perfection of the cortical mechanism for appreciating sounds and 
detecting a very wide range of qualities is associated in the human brain with 
a remarkable growth and differentiation of the auditory area of the cortex.** 
As intercommunication between members of a social group became a matter of 
“* Brodmann, op. cit., p. 144, 
