September 26, 19 12] 



NATURE 



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 

 €rectness it liberated 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 the primitive ape-man could only 

 attempt once his arm was completely emancipated 

 from the necessity of being an instrument of pro- 

 gression, 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 

 Pitliecanthropus,'" and to a less marked degree, 

 Xeanderthal 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 in Homo primi- 

 geniiis, his small prefrontal region, if we accept Boule 

 and .Anthony's statements, is sufficient evidence of 

 his lowly state of intelligence and reason for liis 

 failure in the competition with the rest of mankind. 



Tlie growth in intelligence and in the powers of 

 discrimination no doubt led to a definite cultivation of 

 the a?sthetic sense, which, operating through sexual 

 selection, brought about a gradual refinement of the 

 features, added grace to the general build of the 

 body, and demolished the greater part of its hairy 

 covering. It also led to an intensification of the 

 sexual distinctions, especially by developing in the 

 female 'ocalised deposits of fatty tissue, not found in 

 the apes, which produced profound alterations in the 

 general form of the body. 



Right-handedness. 



To one who considers what precisely it means to 

 fix the attention and attempt the performance of 

 some delicately adjusted and precise action it must 

 be evident that one hand only can be usefully employed 

 in executing the consciously skilled part in any given 

 movement. The other hand, like the rest of the 

 muscles of the whole body, can be only auxiliary 

 to it, assisting, under the influence of attention, either 

 passively or actively, in steadying the body or helping 

 the dominant hand. Moreover, it is clear that if one 

 hand is constantly employed for doing the more 

 skilled work, it will learn to perform it more orecisely 

 and more successfully than either would if both were 

 trained, in spite of what ambidextral enthusiasts may 

 say. Hence it happened that when nature was 

 fashioning man the forces of natural selection made 

 one hand more apt to perform skilled movements 

 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 affecting 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 



^- Eut;. Dubois, 

 'roc. Fourth I 

 899, p. 81. 



l-'_F!ouIeaml Anthony, " 1 

 'nts," L'Atitfiro/iolfgi 



NO. 2239, VOL. 90] 



narks nron the Brain-cast of Pithecanthropus," 

 Cong. Zool., August, 1898, published Camb.. 



; fossile de la Chapelle- 

 II, p. 50. 



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 man- 

 kind 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 much more common than left-handedness is still 

 quite obscure. The superiority of one hand is as old 

 ns 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 at- 

 tempted 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 ad- 

 joining 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. 



The Origin of Speech. 



[This argument was elaborated to explain the origin 

 of speech. The increasing ability to perform actions 

 demanding skill and delicacy received a great impetus 

 when the hands were liberated for the exclusive cul- 

 tivation of such skill : this perfection of cerebral con- 

 trol over muscular actions made it possible for the 

 ape-man to learn to imitate the sounds around him, 

 for the act of learning is a training not only of the 

 motor centres and the muscles concerned, but also of 

 the attention, and the benefits that accrued from 

 educating the hands added to the power of controlling 

 other muscles, such as those concerned with articulate 

 speech. 



The usefulness of such power of imitating sounds 

 could be fully realised in primitive man, not only 

 because he had developed the parts of the brain which 

 made the acquisition of such skill possible, but also 

 because he had acquired, in virtue of the development 

 of other cortical areas, the ability to realise the sig- 

 nificance and learn the meaning of the sounds heard.] 



I do not propose to discuss the tremendous impetus 

 that the invention of speech must have given to 

 human progress and intellectual development, in 

 enabling the knowledge acquired by each individual 

 to become the property of the community and be 

 handed on to future generations, as well as by supply- 

 ing in words the very symbols and the indispensable 

 elements of the higher mental processes. 



We are apt to forget the immensity of the heritage 

 that has come down to us from former generations of 

 man, until we begin dimly to realise that for the vast 

 majority of mankind almost the sum-total of their 

 mental activities consists of imitation or acquiring and 

 using the common stock of beliefs. For this 

 accumulation of knowledge and its transmission to 

 our generation we are almost wholly indebted to the 

 use of speech. In our forgetfulness of these facts 



