622 



SCIENCE 



[N. S. Vol. LI. Ko. 1330 



currents beyond the safe haven of calm and 

 well-considered evaluation of all factors in 

 the problem. 



Competent naturalists of wide experience in 

 many scientific fields are, however, continually 

 bringing forth new confirmatory evidence 

 that the direction of the evolutionary process 

 is to some extent and in some way determined 

 from within and that the course of differ- 

 entiation of organic forms is not in its en- 

 tirety directly and passively shaped by the 

 environmental mold. That these internal 

 factors are ultimately to be referred to the 

 reaction between the living substance and its 

 environment was clearly recognized by Eimer, 

 as is shown by the following quotation:* 



In my view development can taie place in only 

 a few directions because the constitution, the ma- 

 terial composition of the body, necessarily deter- 

 mines such directions and prevents indiscriminate 

 modification. But througi the agency of outward 

 influences the constitution must gradually get 

 changed. The organisms will thus acquire more 

 and more physiological individuality and respond to 

 outward influences more and more in a manner 

 harmonizing with their specific individuality — and 

 so new directions of development will be produced. 



Elmer's further contention that this con- 

 ception implies the unqualified acceptance of 

 the inheritance of acquired characters has 

 doubtless been an obstacle to the more general 

 approval of his views. To this point we shall 

 return. 



As the currents of thought regarding the 

 truth of evolution in general drifted more or 

 less impotently in a sea of speculation until 

 Lamarck, Darwin, DeVries and others con- 

 fined it within scientifically definable banks 

 by presenting plausible explanations of the 

 possible mechanism of the process, so ortho- 

 genesis has remained an ill-defined and at 

 times quasi-mystical hypothesis as long as 

 we had no comprehensible account of the 

 causative factors which may direct the course 

 of future differentiation. It may be regarded 

 as established that orthogenesis in some form 



5 "Senescence and Eejuvenescence," Chicago, 

 1915. 



* Loc. cit., p. 22 



is an evolutionary factor. But what of the 

 method ? 



ChiW has laid down some general prin- 

 ciples which point the way in this inquiry. 

 ITndifierentiated tissues with active metabo- 

 lism (termed tissues of the " young " type by 

 Child) contrast sharply with the more stable 

 and matm'e tissues whose protoplasm has as- 

 sumed characteristic structural patterns in 

 adaptation to specific functions (muscle, 

 gland, etc.). The tissue patterns of the latter 

 group not only maintain their individuality 

 during the life of the organism, but their 

 stability extends deeper into the hereditary 

 organization of the species and their char- 

 acteristic forms run true in successive gener- 

 ations. There is accordingly, as Child ex- 

 presses it, a secular change in the character 

 of protoplasmic organization in the direction 

 of a fixation or stabilization of the more 

 labile and metabolically active tissues of the 

 embryonic or generalized type into more 

 highly specialized and stable patterns. This 

 process of evolution of form is, of course, 

 concomitant with a differentiation and fix- 

 ation of heritable behavior patterns. 



The general physiological processes involved 

 here have been analyzed by Child and the 

 underlying physico-chemical apparatus has 

 been experimentally studied in an illumi- 

 nating series of researches on bio-electric 

 phenomena and their inorganic analogies by 

 E. S. Lillie." 



This process of progressive maturing of 

 tissue in the course of evolution is not differ- 

 ent in fundamental biological character from 

 that seen in the course of ontogenetic develop- 

 ment, and both are expressions of more efil- 

 cient adjustment of the living substance to 

 6 ' ' Transmission of Activation in Passive Metals 

 as a Model of the Protoplasmic or Nervous Type 

 of Transmission," Science, N. S., Vol. 48, 191i8, 

 pp. 51-60. "Heredity from the Physico-chemical 

 Point of View," Biol. Bui, Vol. 34, 1918, pp. 

 65-90. "Nervous and Other Forms of Proto- 

 plasmic Transmission, ' ' Soi. Mo., Vol. 8, 1919, pp. 

 456-474, 552-567. "Precipitation Structures Sim- 

 ulating Organic Growth. II. A Contribution to the 

 Physico-chemical Analysis of Growth and Hered- 

 ity, ' ' Biol. Bui, Vol. 36, 1919, pp. 225-273. 



