NA TURE 



445 



THURSDAY, SEPTEMBER 6, i{ 



A NEO-LAMARCKIAN THEORY OF 

 EVOLUTION. 

 A Theory of Development and Heredity. By Henry B. 

 Orr, Ph.D., Professor at the Tulane University of 

 Louisiana. (New York and London : Macmillan and 

 Co., 1893.) 



THE appearance of a new worlc on the causes of evo- 

 lution, by an American biologist, raised the hope 

 that more solid arguments would be forthcoming in 

 favour of the conclusions accepted by so many well- 

 known writers and workers on the other side of the 

 Atlantic. This hope was doomed to disappointment, 

 the evidence adduced being even more slender than 

 usual, and the conclusions even more rash. 



.'Vccording to a view which has been recently put for- 

 w.ird by Lamarckian writers, the facts of adaptation are 

 explained by the supposition that organisms possess such 

 a constitution that they arc compelled, by the incidence 

 (if external forces, to react adaptively, viz. by the produc- 

 tion of useful variations. This view appears to be sup- 

 ported by the author (chapter i.), although no evidence 

 is brought forward in favour of it. The hypothesis in 

 question seems to be little more than the old "internal 

 developmental force," or " innate tendency towards per- 

 fection," in a modern dress. Furthermore, a little con- 

 sideration of the essential nature of adaptations proves 

 the futility of any such attempt at explanation. The 

 ultimate objects of adaptations are to obtain food, to 

 escape enemies, or to subserve reproduction. In the 

 vast majority of cases adaptations are relative to the con- 

 dition of other individuals of the same and other species 

 — a condition which is and has been continually chang- 

 ing. But the environment with which the organism is 

 in continual contact, and which is presumably sup- 

 posed to bear a pre-eminent part in working these 

 i useful variations, is the inorganic environment. So 

 that stimuli provided by one form of environment are 

 ; looked upon as the direct causes of adaptations which 

 I are essentially related to another and very different 

 ' environment. It would be necessary, in order to make 

 the suggestion valid, to prove that the changes in the 

 organic environment which render some adjustment of 

 adaptation necessary, are invariably accompanied by 

 I corresponding changes in those forces (chiefly inorganic) 

 ! by which it is believed that the adjustment is effected. 

 In discussing " the limits of natural selection," the 

 following supposition is believed to constitute an in- 

 fuperable objection to VVeismann s theory of heredity, 

 viz. "the supposition that the germ-plasm may exist in 

 the body and still be no more affected by the changes 

 which pass over the body than if it were enclosed in an 

 hermetically sealed vial." It is well known that in all his 

 later writings Weismann has abandoned the hypothesis of 

 a germ-plasm endowed with an almost resistless stability. 

 I''Ut the admission of the converse supposition, that the 

 erm-plasm is profoundly affected by the external forces 

 wliich also affect the body, is very far from the admis- 

 sion that acquired characters are transmitted ; and it is 

 this latter, and nothing less, which is required as a 

 NO. 1297, "^'OL. 50] 



foundation for the Lamarckian hypotheses, as, indeed, 

 the author freely admits. In order to prove that the one 

 proposition involves the other, it would be necessary to 

 show that an external force producing a certain effect on 

 the body must produce, upon a totally different thing — 

 the germ-plasm — not, indeed, the same effect, but its 

 precursor. 



Considering " the many cases of wholesale destruction 

 of animals— for instance, the killing of countless fishes 

 by a sudden change in the temperature of the ocean, 

 the killing of birds and insects by cold and storms of 

 wind and rain, and the killing of myriads of organisms 

 of all kinds by circumstances over which they have no 

 control, and from which no mere individual variations 

 could save them," the author is led " to doubt that 

 natural selection acts with such mathematical accuracy 

 in accumulating slight individual variations." It is diffi- 

 cult to understand the grounds upon which the non- 

 operation of natural selection in certain kinds of destruc- 

 tion is held to cast doubts upon the efficiency of its 

 action when it does come into operation. Furthermore, 

 it is easy to point to results which are consistent with 

 the view that natural selection may act " with mathe- 

 matical accuracy " even in the class of cases brought 

 forward. The peculiar condition of the wings of insects 

 living in islands in stormy zones, and a power of resist- 

 ing temperature related to the needs which follow from 

 the geographical distribution of plants and animals, may 

 be cited as examples. 



The author quotes with approval Prof. Cope's conten- 

 tion that " the useful additions which have constituted 

 certain genera, families, orders, &c., what they are," were 

 produced as a direct consequence of needs, and were not 

 formed first and selected afterwards, inasmuch as "it 

 would be incredible that a blind or undirected variation 

 should not fail, in a vast majority of instances, to pro- 

 duce a single case of the beautiful adaptation to means 

 and ends which we see so abundantly around us. The 

 amount of attempt, failure, and consequent destruction 

 would be preposterously large, and in nowise consistent 

 with the facts of teleology as we behold them." 



This antithesis suggests that it is believed that "the 

 useful additions " were fully formed as complete organs 

 or parts before they were selected. According to the 

 theory of natural selection, however, such " additions " 

 have been led by selection from the very first— from the 

 time when the parent organ or part first began to be 

 used for a new purpose (for such is almost invariably 

 the origin of the last " addition")— right back to the 

 remote period when the original ancestor of a long 

 succession of organs and parts came into being. But 

 even accepting Prof. Cope's antithesis, surely, when w-e 

 consider the slow succession of forms throughout geo- 

 logical time, and the amount of extinction which took 

 place in every generation, we may accept his conclusion 

 as to the amount of " attempt, failure, and consequent 

 destruction," and reply that on this very account the 

 Lamarckian explanation is extremely improbable, inas- 

 much as it would imply a direct and rapid evolution, 

 whereas we know that evolution has been slow and 

 interrupted. 



Unnecessary confusion has been introduced into the 

 discussion of instincts by the inclusion under this term 



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