94 



£^CIENGE 



[N. S. Vol. XXXIII. No. 838 



'organic response '^ 

 Kecent events in the field of evolution 

 comprehend a number of movements and 

 accomplishments of extraordinary interest. 

 The rediscovery of the facts of alternative 

 inheritance, the formulation of the con- 

 cepts of equivalent, balanced, paired or 

 differential characters, the results of sta- 

 tistical studies of variability, the analyses 

 of species of various constitution by pedi- 

 gree cultures, in which the value of fertili- 

 zation from various sources is carefully 

 measured, the distinction of the biotype or 

 genotype as a hereditary entity, the recog- 

 nition of the possibilities in the action of 

 pure lines vs'ithin a specific group, the cyto- 

 logical contributions of fact and forecast 

 upon the physical aspects of heredity, and 

 lastly the presentation of the facts and 

 allowable generalizations identified with 

 the mutation theory, comprise a series of 

 advances, of accretions to knowledge, fur- 

 nish a broadened foundation for biological 

 science and disclose additional possibilities 

 in all lines of experimental research with 

 living things, besides opening up new 

 realms for speculative thought and stimu- 

 lating the scientific imagination to renewed 

 fruitfulness. 



The pressure of undisciplined evidence 

 bearing upon almost all phases of evolution 

 has awakened a freshened chorus of 

 voices crying the virtues of special inter- 

 ests and extolling the sufficiency of theories 

 dignified by age and more or less weighty 

 with authority. Those busy with vitalism 

 of various patterns have spun a moiety to 

 mend the breaks in the fragile web of their 

 gossamer tissue made by the impact of new 

 facts. Isolation and geographical distri- 

 bution have again been elaborated to ac- 

 count for all differentiation and what their 

 ^Abstract of presidential address, Society of 

 American Naturalists, Ithaca, New York, Decem- 

 ber 29, 1910. For full text see American Nat- 

 uralist for January, 1911. 



exponents are pleased to term speciation. 

 The anticipatory formation of structures 

 in a rudimentary condition with a long 

 prefunetional progress, guided by the mor- 

 phological possibilities and actuated by in- 

 ternal impulses, has again been offered to 

 us, fortified by some facts and much clever 

 logic, in such manner as to avoid most of 

 the serious objections offered, except those 

 of physiological morphology. 



Natural selection with diverse meanings 

 and manifold implications, has been made 

 to explain development, differentiation and 

 general evolutionary progress, and the 

 tumult is still great about the idea of mu- 

 tation. Undeniable occurrences of salta- 

 tory changes in hereditary lines are 

 numerous and well known, yet it is prob- 

 able that the importance of mutation as a 

 general procedure varies in different 

 groups of organisms and certain that many 

 shades of opinion as to its exact part in 

 the evoltition of living things will always 

 be held. 



The situation with regard to the theory 

 which predicates direct adjustment of the 

 organism, quickly or slowly, as the case 

 may be, to environic factors, and the full 

 inheritance of the alterations constituting 

 such variations is far more serious. The 

 various corollaries of this theory have the 

 force of a certain obviousness, its assump- 

 tions have been of ready service to the 

 systematist and biogeographer, and its con- 

 clusions have long been tolerated in the 

 absence of decisive tests which are not to 

 be easily made or readily carried out. The 

 time has now arrived, however, when the 

 claimants for Neo-Lamarckianism and all 

 of its conclusions must show cause for its 

 further consideration, or else allow it to 

 drop from the position of being seriously 

 taken as a possible method of evolutionary 

 advance. That no subject is the center of 

 a wider interest is amply demonstrated by 



