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SCIENCE 



[N. S. Vol. XL. No. 1024 



size and proportions of parts serve to distin- 

 guish them. Yet they are so distinct genet- 

 ically that they never cross naturally and all 

 attempts to cross them artificially have thus 

 far failed. No one would, I think, advocate 

 the idea that one had arisen from the other 

 by unit character variations, such as distin- 

 guish M. rattus from M. alexandrinus or 

 striking tame varieties of the Norway rat 

 from the wild species. The differences in 

 these latter cases are unquestionable, and their 

 genetic behavior clear, but if we call forms so 

 distinguished species it is evident that we are 

 applying the term on the basis of very; differ- 

 ent phenomena from those which serve to dis- 

 tinguish M. alexandrinus from M. norvegicus 

 or M. musculus. In these cases the observ- 

 able differences are quantitative and their 

 genetic behavior unljnovsm. There is small 

 reason for considering them unit character 

 differences. It is of course possible so to re- 

 gard them if one conceives of unit characters 

 or factors in such cases as very numerous and 

 singly with small effect, in accordance with 

 the principle of ISTilsson-Ehle. But so to con- 

 ceive of a unit character is to rob it entirely 

 of that which the theory of discontinuity in 

 the evolution of species requires and which 

 Bateson seeks to establish. Multiple unit 

 characters presenting an apparently continu- 

 ous series would also have no selectional value 

 superior to that of a.. truly continuous series 

 of variations, the conception which Bateson 

 combats. 



Bateson devotes one of the most valuable 

 chapters of his book to the subject of adapta- 

 tion, without either reaching or attempting to 

 reach any explanation of it. Indeed he rather 

 deplores the fact that so much attention has been 

 devoted to the adaptation of species before we 

 have arrived at any clear notion as to what 

 species are or how they arise. The chief value 

 of Bateson's discussion of this question lies in 

 the destructive criticism which he offers of 

 the attempted explanation of adaptation as a 

 direct response of the organism perpetuated 

 by heredity. He passes over the earlier dis- 

 cussions concerning the inheritance of ac- 

 quired characters, but deals with its recent 



vigorous renewal by Semon, who regards 

 heredity as analogous with memory or habit. 

 Bateson holds that an analogy with psychic 

 phenomena is no explanation, among other 

 reasons because the explanation is necessarily 

 more complicated than the thing explained. 

 The evidence on which Semon relies to estab- 

 lish the inheritance of acquired characters, 

 Bateson deals with at some length. He shows 

 the inadequacy of the oft-cited temperature 

 experiments with lepidoptera to show either an 

 increased variability due to experiment or its 

 inheritance. The case of Schubeler's wheat 

 adapting itseH automatically to the shorter 

 season of Norway is subjected to destructive 

 criticism, as is also the case of Brown- 

 Sequard's guinea-pigs, so often brought for- 

 ward, so often shown to be of no consequence. 

 Special attention is given to the recent work 

 of Kammerer at Vienna upon salamanders, on 

 which Semon places great reliance. By keep- 

 ing land salamanders in water and vice versa, 

 Kammerer claims to have modified the struc- 

 ture and habits of these animals permanently, 

 the young inheriting the acquired modifica- 

 tions of the parents even when restored to nor- 

 mal conditions, and the inherited effect in- 

 creasing from generation to generation upon 

 continuation of the experimental conditions. 

 Bateson shows that these extensive claims are 

 based on wholly inadequate experiments, that 

 the author is unable or unwilling to produce 

 specimens of the modified structures which he 

 claims to have obtained, and that unless his 

 observations are independently confirmed it 

 is " easier to believe that mistakes of observa- 

 tion or of interpretation have been made than 

 that any genuine transmission of acquired 

 characters has been witnessed." 



" Meanwhile there is no denying that the 

 origin of adaptational features is a very 

 grave difficulty. With the lapse of time since 

 evolutionary conceptions have become a uni- 

 versal subject of study that difficulty has, so 

 far as I see, been in no wise diminished. But 

 I find nothing in the evidence recently put 

 forward which justifies departure from the 

 agnostic position which most of us have felt 

 obliged to assume." 



