24 The Recapitulation Theory and Human Infancy 



"We have endeavored to demonstrate that a natural classifi- 

 cation can be made by means of a system of analysis in which 

 the individual is the unit of comparison, because its life in all 

 its phases, morphological and physiological, embryo, larva, ado- 

 lescent, adult, and old (ontogeny), correlates with the morpholog- 

 ical and physiological history of the group to which it belongs 

 (phylogeny). 



"All modifications and variations in progressive series tend 

 to appear first in the adolescent stages of growth, and then to be 

 inherited in successive descendants at earlier and earlier stages 

 according to the law of acceleration, until they either become 

 embryonic or are crowded out of the organization and replaced 

 in the development by characteristics of later origin." 32 



The term acceleration is not to be understood as implying neces- 

 sarily a quicker development. On the contrary, "an animal 

 having accelerated development of characteristics does not 

 necessarily have a quick development, but may grow, so far 

 as time is concerned, even more slowly than others of its own 

 group." 33 The accelerated characteristic merely takes a new 

 relative position in the whole ontogeny by reason of the omis- 

 sion or suppression of the earliest or older stages and the addition 

 of adaptive phases at the adult end. 



The evolutionary explanation of the law is as follows: 



"We can fully understand the phenomena of acceleration 

 in development only when we begin by assuming that the char- 

 acteristics last introduced in the history of any type were more 

 suitable to the new conditions of life on the horizon of occurrence 

 of the species than those which characterized the same stock 

 in preceding horizons. These characters would then necessarily, 

 on account of their greater usefulness and superior adaptability, 

 interfere with the development of the less useful ancestral stages,, 

 and thus tend to replace them." 34 



Two important additions to this law of acceleration were 

 made by the distinguished American naturalist, Cope, who* 

 presented an independent formulation of the law itself in the 

 year 1866 35 — a year significant for recapitulation, for as has 

 been noted, it gave expression to three original statements of 

 the law, namely, those of Haeckel, Hyatt, and Cope. One of 



" Genesis of the Arietidae, Smithsonian Contributions to Knowledge, 1890, pref- 

 ace 



"IUd., p. 40, footnote. 



"Ibid., pp. 44, 45. 



it Primary Factors of Evolution, 1896, p. 9. 



