24 THE METHOD OF DEVELOPMENT 



as infant, as well as in the adult stage. Progressive variations, 

 occurring at the end of the development, add to the parental total 

 of development : retrogressive variations subtract from it ; both 

 kinds, occurring during development interpolated into it render it 

 inaccurate, and, in the process of many generations, very inaccurate. 



43. But, if the child recapitulates the development of the parent, 

 the latter also recapitulated that of the grandparent, who in turn 

 recapitulated that of the great-grandparent, and so on up to the 

 first multicellular ancestor. Consider, now, the simplest conceiv- 

 able case of progressive evolution followed by retrogression. 

 Imagine a line of individuals A, B . . . L, M, in whom a structure 

 undergoes uninterrupted increase in a single direction as it were 

 in a straight line by successive progressive variations occurring 

 at the end of the development of each successive individual. 

 Suppose the structure began in B as a variation from A, and 

 underwent evolution by successive steps in C, D, . . . till it reached 

 its culmination in M. Suppose also that it began to retrogress in 

 N, and that it continued to do so uninterruptedly till it quite 

 disappeared in Z. 



44. Consider first the progression. Clearly, since each individual 

 down to M recapitulates the development of his parent and makes 

 in addition another step, the development of B must consist in a 

 recapitulation of A, followed by his own variation. C, again, since 

 he recapitulates B, must first recapitulate A, then proceed to B's 

 variation, and then to his own. D in turn must recapitulate A, 

 then the variations in order of B and C, and then, and then only, 

 proceed to his own variation. M, the last of the race in whom a 

 progressive variation occurs, must found his variation on a re- 

 capitulation of A, plus a recapitulation in orderly succession of the 

 variations of all the intervening ancestors. In other words the 

 development of the structure in M is a recapitulation of its evolution 

 in the race. In no other way that can be conceived could the 

 structure have been evolved. Apply this reasoning to every 

 structure and character in the body, and we perceive that the 

 theory that every individual in his own development climbs his 

 own genealogical tree must necessarily be true. Given the un- 

 questionable fact that the child recapitulates the development of 

 the parent, any method of development other than by a recapitula- 

 tion of the life-history of the race is, not only impossible, but 

 actually unthinkable. One truth necessarily involves the other. 



45. But to say that development is a recapitulation of the life- 

 history is one thing. To say that in every instance it presents a 



