If, when tested, they should be found correct, they would be sufficient answer to several of the theories of right-handedness heretofore urged, as has been already remarked. The rise of the phenomenon must be sought, therefore, in more deep-going facts of physiology than such theories supply. Furthermore, if we go lower in the animal scale than man, analogies for the kinds of experience which are urged as reasons for right-handedness are not present; animals do not carry their young, nor pat them to sleep, nor do animals shake hands!
A full discussion would lead us to the conclusion that dextrality is due to a difference in development in the two hemispheres of the brain, that these differences are hereditary, and that they show themselves toward the end of the first year.
It is a singular circumstance that right-handedness and speech are controlled by the same hemisphere of the brain and from contiguous areas. It would explain this--and at the same time it seems probable from other considerations--if we found that right-handedness was first used for expression before speech; and that speech has arisen from the setting aside, for further development, of the area in the brain first used for right-handedness. Musical expression has its seat in or near the same lobe of the brain.
_The Child's Mental Development in General_.--The actual development of the child, as observations from many sources indicate it, may be sketched very briefly in its main outlines. It is probable that the earliest consciousness is simply a mass of touch and muscular sensations experienced in part before birth. Shortly after birth the child begins to connect his impressions with one another and to show Memory. But both memory and Association are very weak, and depend upon intense stimulations, such as bright lights, loud noises, etc. The things which most effect him at these early stages are those which bring him into conditions of sharp physical pain or give him acute pleasure. Yet it is a remarkable fact that at birth the pain reflex is wanting. His whole life up to about the fourth month turns upon his organic and vegetative needs. At three months the young child will forget his mother or nurse after a very few days. Attention begins to arise about the end of the first quarter year, appearing first in response to bright lights and loud sounds, and being for a considerable time purely reflex, drawn here and there by the successive impressions which the environment makes. With lights and sounds, however, movements also attract the infant's attention very early; and the passage from reflex attention to a sort of vague interest seems to arise first in connection with the movements of the persons about him. This interest goes on to develop very rapidly in the second half year, in connection more particularly with the movements which are associated with the child's own comfort and discomfort. The association of muscular sensations with those of touch and sight serves to give him his first clear indications of the positions of his own members and of other objects. His discrimination of what belongs to his own body is probably aided by so-called "double touch"--the fact that when he touches his own body, as in touching his foot with the hand, he has two sensations, one in the foot and the other in the hand. This is not the case when he touches other objects, and he soon learns the distinction, getting the outlines of his own body marked out in a vague way. The learning of the localities on his body which he can not see, however, lags far behind. The movements of his limbs in active exploration, accompanied by sight, enables him to build up his knowledge of the world about him. Learning this he soon falls to "experimenting" with the things of space. Thus he begins to find out how things fit together, and what their uses are.