BRAIN DEVELOPMENT AND EVOLUTION. 529 



wliicli the brain surface is increased, do furnish a better index. 

 Second, that this physical co-ordination with increased mental 

 and emotional activity, this physical manifestation of developing 

 mind, has already taken place in the brains of apes, and is fore- 

 shadowed in the lower species of quadrumana.* Furthermore, 

 from an intelligent standpoint this is precisely what might have 

 been expected. 



Let us bear in mind that out of all the innumerable, almost 

 infinite number of variations, eccentricities, and oddities, how- 

 ever slight, found by examining each individual microscopically 

 (if such a thing were possible), those minute changes and pecul- 

 iarities, and those only, will be preserved in the long run, and 

 after many generations, which are of such a character as to 

 secure for their possessors more vigor and longevity than those 

 without them can possibly have, simply because vigor and lon- 

 gevity vastly increase the opportunities of heredity. 



Now the size and weight of the brain in proportion to the size 

 and weight of the body is just one of those important propor- 

 tions of parts which would make for or against the vigor and 

 long life of the individual in a marked degree. One other con- 

 current condition, however, Avould perhaps be of even greater 

 importance, and it is this : that the height, size, form, and weight 

 of the whole body should have the fittest adaptation to its* cir- 

 cumstances and to the work required of it, in order to secure the 

 greatest vigor and longest life, and so at last to become the 

 characteristic of every member of the species. So it is plain that 

 the brain as to size and weight must stand two tests. It must 

 not only bear the best possible proportion to the body, but that 

 body must be of the fittest size and weight to meet successfully, 

 and for the longest period, all that it is compelled to encounter, 

 and thus to succeed above all other less fortunate individuals in 

 finally making this double due proportion the property and the 

 universal characteristic of the species. Within these limitations 

 and conditions, but not otherwise, the size and weight of the 

 brain and consequent cranial capacity are doubtless subject to 

 the amount of mental instinctive, receptive and emotional activ- 

 ity demanded of it, and carried on within it. In shorter phrase, 



* Functions of the Brain, by David Terrier, M. D., F. R. S., Professor of Forensic Medi- 

 cine, King's College, London, published by Smith, Elder &Co., 51 Waterloo Place, London, p. 

 297 : " The brain of man is constructed on the same type as that of the monkey, and essen- 

 tially the same primary fissures and convolutions are recognizable in both, the chief differ- 

 ences consisting in the greater complexity of the convolutional arrangement of the human 

 brain, caused by the development of the numerous secondary and tertiary gyri, which tend 

 to obscure the simple type of the simian brain. These differences are more marked in the 

 adult and highly developed brain, but are less pronounced in the foetal human brain." See, 

 also, Ecker on the Convolutions of the Human Brain, translated by Gallon, etc. 

 VOL. XLVI. 38 



