THE HISTORY OF ANIMAL LIFE 395 



While it has been impossible to show by experimental methods 

 that acquired characters are inherited in the Lamarckian sense, still 

 some biologists hold, and rightly so, that the experience of any one 

 man, or for that matter the period of observation embracing the 

 whole history of human intelligence, constitutes only an exceedingly 

 minute fraction of the whole time during which evolution has been 

 in progress. They further point out that Man cannot repeat this nat- 

 ural sequence of geological and climatic change and that therefore 

 the most reliable evidence for evolution must be drawn by inference 

 from paleontological and anatomical comparisons. This leads them 

 to a Lamarckian interpretation of evolution. 



Orthogenesis. Still another aspect of the problem of the nature 

 of evolution concerns us, namely, that of orthogenesis, or of defi- 

 nitely directed evolution. This aspect of evolution was first pre- 

 sented in 1898 by Eimer. Briefly stated, this interpretation points 

 out that the evolution of modern forms has followed a perfectly 

 determined direction, complex forms arising in an orderly sequence 

 as a complex adult arises in the development of an individual from 

 the egg. In its first form Eimer adopted a Lamarckian interpretation 

 of orthogenesis. The theory is capable of being easily converted into 

 a vitalistic interpretation by assuming that the directive influence is 

 a supernatural power. 



Limitations of the Theories. One must distinguish sharply 

 between the theories of the mechanism of evolution and the facts 

 that constitute the record of evolution. The theories represent pos- 

 sible interpretations of the mechanism in the light of the facts of 

 evolution. The facts are not open to question; they may be exam- 

 ined by anyone who has the interest to do so. The record is clear. 

 The direction and pace of change from the simple toward the 

 complex are obvious when the evidence is examined. Intellectual 

 honesty forces an acceptance of the fact that evolution has occurred, 

 as it forces one to conclude that the present status of national life in 



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