66 The Recapitulation Theory and Human Infancy 



for their exercise and adult determination, and brings with it 

 coincidently a corresponding amount of helplessness on the part 

 of the young, demanding parental care and protection. Con- 

 sciousness is especially associated with these complex and intri- 

 cate connections of the higher ganglia, and very little or not at 

 all with the mechanical reactions of the lower centers. Thus 

 arises conscious intelligence with its differentiation in emotion, 

 memory, perception and reasoning, and volition. In the case 

 of man this whole evolution has reached its acme, so that brain 

 tissues are largest, convolutions of the cerebral surface are most 

 noticeable, the highest psychic powers are manifested, the period 

 of infancy is longest, and parental solicitude most intense. The 

 process has been continued from savagery to civilization. Paren- 

 tal care first provided by the mother alone, is later assumed by 

 the father also, and as the succession of maturing young prolongs 

 the period of conjugal association, with its incidental fostering- 

 of family sympathy and feelings of attachment, the family 

 is born, its elaboration giving rise to social as contrasted with 

 merely gregarious relationships. Thus the omission in Darwin's 

 account of the descent of man is made good, as Fiske believed, 

 and the helpless babe is shown to be the instrument of man's 

 peculiarly social and humane endowment. 



Fiske's later statements added little to the original one, but 

 other students have illustrated and elaborated certain features of 

 the theory, while certain contributions must be regarded as posi- 

 tive additions to it. The American naturalist, Marsh, had found 

 from a study of fossil remains evidence of a marked increase in 

 cerebral substance in recent mammals as compared with their re- 

 latives of the lower tertiary epochs. Eocene brains were small, 

 hardly larger than those of the reptiles in some cases. There was 

 a gradual increase in the size of the mammalian brain through the 

 tertiary period, generally in the cerebral hemispheres. The same 

 law holds good for birds and reptiles from the Jurassic to the 

 present. The brain of a vigorous progressing race was relatively 

 large, that of a declining race relatively small. The brain 

 size of young was found to be proportionately greater than that 

 of adult. This brain increase was regarded by Marsh as an 

 important element in survival. 6 



*Amer. Journ. of Sci., Vol. VIII, 1874; abstract in Nature, Vol. XXXII, p. 562. 



