304 



SCIENCE. 



[N. S. Vol. XXIV. No. 610. 



The word evolution is often used as the 

 name of the whole study of development — a 

 branch of biology which includes' the consid- 

 eration of all the attendant factors or groups 

 of phenomena. This generalized use is often 

 convenient and wholly unobjectionable, but as 

 soon as the question of the causes of evolution 

 is raised the word obtains a much more ex- 

 plicit sense, serving then to designate the con- 

 crete physiological process in which the char- 

 acters of species are changed. To insist that 

 the progressive transformation of species be 

 called variation, and not evolution, introduces 

 a merely gratuitous confusion of words, since 

 it removes both these terms, variation and 

 evolution, from their primary significations. 



The essential idea of variation is in its 

 application to differences caused by the en- 

 vironment, that is, to transverse contempo- 

 raneous displacements among the individual 

 members of a species, and not to the progress- 

 ive, chronologically extended, longitudinal 

 changes which represent the evolution of the 

 species as a whole. These are two distinct 

 modes of organic motion. To call them both 

 variation does not prove that they are the 

 same; it only facilitates such an assumption 

 and tempts the unwary to take it for granted 

 that anything which can modify or displace 

 individual organisms in the transverse direc- 

 tion of variation, can also cause species to 

 move in the longitudinal direction of evolu- 

 tion. 



The kinetic conception avoids the verbal 

 pit-fall and finds fundamental differences be- 

 tween the transverse contemporaneous varia- 

 tion of individuals and the longitudinal suc- 

 cession or gradual modification of form or 

 structure in the species as a whole. Other 

 forms of expression become necessary in order 

 that the two kinds of phenomena formerly 

 covered by the variation blanket can be com- 

 pared and contrasted. 



At such points the interests of general lit- 

 erature and of professional science often di- 

 verge widely. Specialists who are unwilling 

 to use the word evolution in a definite physi- 

 ological sense would have preferred some more 

 technical means of designating this process 



of change in species. It might have been 

 called, for example, symbasic prostholysis, in 

 allusion to the fact that it is accomplished 

 through the association of organisms into in- 

 terbreeding groups rather than as a result of 

 the environmental influences which induce 

 variations. The species, and not the indi- 

 vidual, is the unit of evolution; there are as 

 many evolutions as there are segregated 

 groups of organisms. 



* The whole process of development of the 

 organic world, from its beginning to its end,' 

 which Dr. Ortmann prefers to call evolution, 

 is a merely historical conception and not a 

 biological process at all, except as it is made 

 up of the separate evolutions of the millions 

 of species of which the ' organic world ' is 

 composed. What is to be gained of clearness 

 of thought or of expression by calling the 

 general aggregate evolution, while denying 

 this name to the specific units of development, 

 is not easy to perceive. Dr. Ortmann would 

 scarcely have thought to beguile us with the 

 hollow formula that species change by varia- 

 tion and that variation therefore causes evolu- 

 tion. But why otherwise should it have ap- 

 peared so astonishing to find the word evolu- 

 tion used in a particular as well as in a gen- 

 eral sense? It is necessary here to fully re- 

 ciprocate with Dr. Ortmann and 'positively 

 decline to accept ' his conception of evolution, 

 if, as now appears, it is something which takes 

 place in the organic world at large, but does 

 not appear in the component species. 



The jury must decide who has meditated the 

 greater violence to the English language. It 

 is certainly Dr. Ortmann who proposes the 

 greater restriction of the word evolution, for 

 he would permit its use only in the general 

 and indefinite sense, as applying to the or- 

 ganic cosmogony as a whole, while I would 

 recognize in addition a definite physiological 

 meaning, when questions of evolutionary 

 causes are being discussed. 



The conception of spontaneous change in 

 the characters of species may not be correct, 

 but it is at least a conception, and it permits 

 evolution to be thought of as a phenomenon 

 separate and distinct from accidents of en- 



