42 The Recapitulation Theory and Human Infancy 



depreciation of the inheritance of acquired characters which 

 took place in the latter part of the last century, and the appli- 

 cation of experimental methods to the facts of growth and de- 

 velopment (Experimental Zoology, Experimental Embryology, 

 The Mechanics of Development, Experimental Morphology). 

 The inheritance of acquired characters favored a conception 

 of variation at the adult end of ontogeny in response to the 

 direct action of the environment. It was one of the chief in- 

 terests of Hyatt to show how these latest acquisitions in devel- 

 opment became successively inherited in such fashion that 

 they left in the ontogeny a true record of the changes in descent, 

 and it is well known that the three men whose authority gave 

 the greatest prestige to recapitulation, Darwin, 67 Haeckel, 

 and Spencer, all acknowledged the direct action of the environ- 

 ment as a source of variation. 



With the progress of the study of development the complex- 

 ity of the whole matter of growth and differentiation of struc- 

 ture became apparent, and the implications for the dominant 

 idea of recapitulation were pointed out. Wilhelm His, in 1874, 

 in "Unserer Korperform," gave expression to his dissatisfac- 

 tion with HaeckePs view of phylogeny as the mechanical cause 

 of ontogeny, and introduced the idea of forces inherent in the 

 process of growth itself to account for its changes of form. His 

 words are as follows: 



"In the entire series of forms which a developing organism 

 runs through, each form is the necessary antecedent step of the 

 following. If the embryo is to reach the complicated end-forms, 

 it must pass, step by step, through the simpler ones. Each 

 step of the series is the physiological consequence of the preceding 

 stage and the necessary condition of the following. Jumps, or 

 short cuts, of the development process, are unknown in the 

 physiological process of development. If embryonic forms are 

 the inevitable precedents of the mature forms, because the more 

 complicated forms must pass through the simpler, we can under- 

 stand the fact that paleontological forms are so often like the 

 embryonic forms of today. The paleontological forms are 

 embryonal, because they have remained at the lower stage of 



7 " Whatever influence long-continued use or disuse may have had in modifying 

 the limbs or other parts of any species, this will chiefly or solely have effected it 

 when nearly mature, when it was compelled to use its full powers to gain its own liv- 

 ing; and the effects thus produced will have been transmitted to the offspring at a 

 corresponding nearly mature age." Origin of Species, II, 6th ed., London, 1902, 

 p. 613. 



