DEVELOPMENT 449 



in any way to that of other animals and plants, but because this human 

 nature goes far beyond that of these others and reaches values which 

 are probably both permanent and real. With all these more actual 

 human values biology as such has nothing to do save to recognize 

 their existence and to admit its own inadequacy as a science of human 

 nature. 



Fetal Life in a broad sense of the term includes the period of develop- 

 ment between the union of the nucleoplasm of the male and female 

 pronuclei and the completed birth of the child. This is the subject- 

 matter of human embryology, and partly because this science is con- 

 sidered a portion of anatomy rather than of physiology, we do not 

 discuss it here. 



Childhood. The fourteen years or so between birth and puberty we 

 may, although not technically, know as childhood. Its beginning is the 

 separation, for the most part, of the new individual from its mother's 

 body. Its other terminus is the commencement of the time when this 

 new being may in turn become mother or father to another generation. 

 In most all respects childhood merges into adulthood gradually. It is 

 only in the reproductive phase of bodily function that entirely new events 

 begin, although these widely pervade in one way or another both the 

 body and the mind. 



The commencement of childhood so far as the various bodily functions 

 go is likewise gradual in some respects. Yet the unique act of being 

 born, the beginning of respiration, of digestion, of excretion, the changes 

 in the circulation, and the beginning of action in most of the sense-organs 

 make the extra-uterine life sufficiently different from that within the 

 womb. Formerly the fetus was influenced from without itself almost 

 wholly (aside from mechanical impacts wholly) through the mother's 

 blood. Now, however, it begins a much more varied career and becomes 

 more nearly unified with its environment through many various channels 

 and in a large number of respects. As Fiske long ago pointed out, it is 

 because of man's uniquely long childhood more than anything else that 

 his general predominance in the world is due, for meanwhile he imitates 

 his parents. 



The ovum has increased in mass more than nine hundred million 

 times by the time the child is born, and has seen the "division of labor" 

 in case of its original functions go on in hundreds of directions and in 

 thousands of steps. The human animal when born (although made up of 

 cells basally like the ovum) has a cellular tissue-complexity and differen- 

 tiation beyond all understanding. At the birth of the individual these 

 myriad cells take on a new set of relations to each other. The child 

 begins a new group of developmental changes his long second step 

 toward maturity. Let us glance at the most important of these sorts of 

 growth. 



Weight. The average weight at birth of the female child of American 

 parents is about 3150 gm., or 7 Ibs., and that of the male child is 100 

 or 200 gm. more. Largely for the reason that the average infant assimi- 

 29 



