THE 



AMERICAN NATURALIST 



Vol. LV I. March-April No. 643 



ORTHOGENESIS 



SYMPOSIUM ON ORTHOGENESIS BEFOEE THE AMEKICAN 

 SOCIETY OF ZOOLOGISTS, TOEONTO, DECEMBER, 1921 



ORTHOGENESIS FROM THE STANDPOINT OF 

 THE BIOCHEMIST . 



PROFESSOR L. J. HENDERSO^^ 

 Harvard Uxn-ERSiiy 

 It does not seem likely that physical science should 

 have much to say about the theory of orthogenesis. In 

 the first place, it is hard to see what the term means if 

 one adopts a physico-chemical standpoint. In the second 

 place, organic evolution is more remarkable in its morpho- 

 logical aspects than in its chemical and physico-chemical 

 aspects. 



The first point. may be dismissed with a few remarks. 

 Orthogenesis presumably means that evolution has taken 

 place in a straight line or in a very restricted path, and 

 that the straightness of the line depends, at least partly, 

 upon something which is internal to the organism, 

 though, of course, the process may be released by a stim- 

 ulus from the environment. The straightness of the proc- 

 ess must be largely a matter of definition. Physico- 

 chemically, it could hardly mean more than that quanti- 

 tative changes have steadily the same sign over a con- 

 siderable period of time. 



One might, perhaps, adopt such a view, if one c 

 believe, as has been often suggested, that variation is 

 expression of a process which is approaching a condition 

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