NA turb: 



49 



THE SIGNIFICANCE AND SCOPE OF 



NATURAL SELECTION. 



Ueber Bedeutung und Tragweile des Darwin' schen Selec- 



tionsprincips. Von L. Plate, Privatdozent an der 



Universitat Berlin. Pp. 1-153. (Leipzig : W. 



Engelmann, 1900.) 

 T^HE great merit of this interesting and thorough 

 piece of work is its explicit recognition of the 

 principle of selection as an indispensable element in 

 organic evolution. We are in some degree prepared for 

 the author's attitude on this question by the last sentence 

 of his preface, in which he asserts that the principle of 

 selection affords at the present time the only scientific 

 explanation of the harmony existing between the endow- 

 ments of an organism, whether structural or functional, 

 and its surrounding conditions. From this statement it 

 might be supposed that the author not only holds selec- 

 tion to be an essential agent in organic evolution, but 

 that he is also prepared to dispense with the Lamarckian 

 factors, which have certainly been appealed to as fur- 

 nishing an alternative or concurrent explanation of the 

 same harmonious relations between organism and en- 

 vironment. Such, however, as will be seen later, is not 

 the case. 



Nothing could be better than the impartial and judicial 

 spirit of the opening pages, in which the author moves 

 methodically on from point to point, clearing the ground 

 of misconceptions, and disposing conclusively of a long 

 series of well-known but futile objections to the theory of 

 natural selection. Presently he takes in hand the case of 

 the superior oblique muscle of the orbit, and shows 

 admirably how the difficulties disappear on reference to 

 the facts of comparative anatomy. But at this point he 

 lets fall an obiter diction which, in view of his opening 

 declaration, is somewhat startling. The development of 

 a muscle-tendon, he thinks, may be explained as the con- 

 sequence of a pull exercised in a certain direction 

 through many generations. We are thus confronted with 

 a re-entry of Lamarckism ; and, reading on, we find 

 abundant proof that Plate, so far from really holding that 

 the phenomena of adaptation are only to be explained 

 by selection, thinks it necessary to supplement that 

 principle by the hereditary transmission of acquired 

 characters. Thus the parachute-like membranes of the 

 flying squirrels, Galeopithecus, flying lizards, and the like, 

 are considered by him to have originated from a stimulus 

 exercised by the outstretched limbs upon the skin of the 

 sides of the body, the effects of which accumulated for 

 many generations (p. 31). The ischial callosities of 

 monkeys were produced by the sitting posture (p. 36). 

 The loss of hair and development of blubber in the 

 whales may be due to the direct action of water on the 

 skin and subcutaneous connective tissue (pp. 1 1 1, 142). In 

 short, the author leaves us no room to doubt that he 

 believes in use-inheritance, and in the possibility of the 

 transmission of characters however acquired. 



On turning to the grounds for his belief, we find them 

 stated as follows (p. 55) :— (i) All or almost all of the 

 somatic cells may be supposed to contain germ-plasm ; 

 NO. 1646, VOL. 64] 



this is made probable by the phenomena of regenera- 

 tion. Moreover, the whole of the germ-plasm, whether 

 of the somatic or genital cells, may be conceived of as 

 forming a network whose nodes are situated in the nuclei 

 of the different cells. A peripherally-started impulse 

 would be propagated along such a network in all direc- 

 tions, and in this way a somatogenic character might 

 become transmissible by descent. (2) Use-inheritance 

 forms the simplest explanation of co-adaptation. (3) 

 Many phenomena can only be understood by reference 

 to orthogenesis, i.e., the cumulative effect of a stimulus 

 acting through many generations. (4) The gradual 

 dwindling of rudimentary (vestigial) organs must be 

 accounted for by inheritance of the effects of disuse. 



Of these, the first is mainly speculative ; moreover, , 

 were the initial assumptions granted, it would still be far 

 from clearing up the actual mode of the supposed trans- 

 mission. Two of the others have no doubt been felt as 

 difficulties by some of the upholders of natural selection, 

 and have already been pressed home by Herbert Spencer ; 

 but there are other ways of accounting for these and 

 similar phenomena which seem more satisfactory than 

 the recourse to Lamarckians' explanations. Plate very 

 candidly admits that there is at present no direct proof of 

 the transmission of acquired characters, and it is unfortu- 

 nate that he burdens his argument for selection with the 

 unnecessary weight of an unproved and improbable 

 hypothesis. His real reason for declining to rank him- 

 self with the anti-Lamarckian is probably the difficulty 

 that he finds, in common with many others, in assigning 

 selection-value to the early stages of variation. But, as 

 Wallace and others have shown, when the actual varia- 

 tions come to be fairly examined, it appears that ample 

 material for selection exists from the outset. It is 

 worthy of note that Plate himself, in discussing Cunning- 

 ham's strictures on Weldon's experiments with crabs, 

 admits that the latter has virtually shown the selection- 

 value of slight differences of structure. 



A large portion of the treatise is devoted to the subject of 

 sexual selection. An excellent classification of secondary 

 sexual characters is given, and the whole question is treated 

 on broad and generally rational lines. It is to be regretted, 

 however, that the author, in emphasising the slenderness 

 of the evidence for female choice that at present exists, 

 has failed to do justice to the statements of some 

 opponents. An instance of this occurs in the case of an 

 observation of Poulton's, whom Plate represents as having 

 watched the female of such a moth as Saturnia carpini 

 resting motionless amidst a crowd of fluttering males, all 

 of them most eager to pair, but unable to do so until the 

 female, in some way imperceptible to the observer, made 

 her choice. Poulton's interpretation of the facts is some- 

 what curtly rejected, and the subject is dismissed. A 

 reference, however, to the original account will show that 

 the argument is inaccurately given. The moth specified 

 is not Saturnia carpini or one of its allies, but the widely 

 removed Charaeas graminis. On the other hand, 

 Poulton expressly says that the female of Saturnia 

 carpini " in its present condition is certainly passive, and 

 probably always accepts the attention of the first male to 

 arrive.'' The slip would matter little were it not that it 

 has the effect of obscuring Poulton's argument, which 

 rests on the observed facts that the females of some moths 



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