Page Two 



EVOLUTION 



April, 1928 



Ernst Haeckel and the Ontogenetic Law 



By Alexander Goldenweiser 



IF Darwin was the father of evohition, Huxley was its 

 war horse, but Haeckel. the great German Darwinian, 

 was its knight in shining armor. Haeckel's greatest con- 

 tribution to evolutionary theory was probably his ''fun- 

 damental ontogenetic law" which stated that ontogeny 

 recapitulates phylogeny. 

 This meant that every or- 

 ganism in its pre-natal 

 embryonic development 

 recapitulates the stages 

 through which the species 

 of organism had passed 

 in their phylogenetic suc- 

 cession. 

 ' Haeckel's work on this 

 subject was built on the 

 foundation laid down by 

 Karl Ernst von Baer, an 

 Esthonian, who in his 

 "Development of Ani- 

 mals" (published about 

 1828) first made known 

 the facts upon which his 

 own and later Haeckel's 

 theory were based. Baer 

 taught that the many spe- 

 cialized parts of the adult 

 organism, such as the 

 nervous system, the ali- 

 mentary canal and the 

 body wall, developed 

 from embryonic leaf-like 

 layers, four in number 

 (by later investigation re- 

 duced to three), which 

 were identical in all the 

 higher animals. Baer also 

 determined the chief sta- 

 ges of embryonic devel- 

 opment, to wit: first the fertilized egg and its differen- 

 tiation, then the germ-layers, and last the specialized 

 tissues and organs. This sweeping generalization was 

 fully borne out by later investigations. 



While the details of Baer's theory were greatly modi- 

 fied in the course of the intensive biological researches 

 of the middle nineteenth century, its basic kernel with- 

 stood the test of time. In his "General Morphology" 

 (1866), Haeckel was able to set down the features of 

 the ontogenetic law in forty-four theses of which the most 

 important were the following: 1. The development of 

 organisms is a physiological process, depending on me- 

 chanical causes, or physico-chemical movements; 2. On- 

 togenesis, or the development of the organic individual, 

 is directly determined by phylogenesis, or the evolution 

 of the organic stem [phylon) to which it belongs; 3. On- 

 togenesis is a brief and rapid recapitulation of phylogen- 

 sis, determined by the physiological functions of hered- 



ity and adaptation. 



Of these three theses, the second and third are ac- 

 cepted in all modern evolutionary biology, whereas the 

 first has led to much discussion and controversy since 

 the emergence of the vitalists (such as the Berlin em- 



bryologist, Oscar Hert- 

 wig, Hans Driesch the 

 biologist, the philosopher 

 B e r g s o n and many 

 others) who claim that 

 the phenomena of life 

 cannot be wholly explain- 

 ed by physico-chemical 

 laws but require the pos- 

 tulation of a specific vital 

 principle. 



Haeckel, who was at- 

 tacked on all sides — by 

 scientists and theolog- 

 ians alike — spent much 

 time and effort in elabor- 

 ating and substantiating 

 the second and third 

 theses of his theory. In 

 his "Studies of the Gas- 

 trea Theory" (1872-1877) 

 he showed that in all 

 tissue-animals, from the 

 lowest sponges and pol- 

 yps to the highest articu- 

 lata and vertebrata, the 

 multicellular organism 

 developed from the same 

 primitive embryonic form 

 (the gastrula), and that 

 this was the ontogenetic 

 repetition, in virtue of 

 heredity, of a correspond- 

 ing stem-form (the gn^- 

 trea). But Haeckel went further and in his "Anthro- 

 pogeny"' (1874) he illustrated the recapitulation theory 

 on the human organism. In this work he attempted to 

 explain the complex process of individual development, 

 for the whole frame and every part of it, by causal con- 

 nection with the stem-history of the animal ancestry of 

 man. In the last edition of his book Haeckel demonstrated 

 this theory with thirty plates, five hundred engravings 

 and sixty genetic tables. 



In answering his numerous critics, Haeckel also tried 

 to make clear that the ontogenetic process must not be 

 conceived as an exact duplication of the phylogenetic 

 one, but that the former was an abbreviated recapitula- 

 tion of the latter, complicated by condensation, distur- 

 bance or falsification. The biogenetic law, when prop- 

 erly understood, thus comprises two factors, one posi- 

 tive, one negative. The positive factor — palingenesis — 

 reproduced a part of the original history of the stem; 



Ernst Haeckel 



