556 



NATURE 



[April 14, 1898 



and eat it" and the hen which " selects that mate which 

 by his song or otherwise excites in greatest degree the 

 mating impulse," although doubtless perfectly true in 

 itself, leaves unexplained and indeed unexpressed the 

 fact that the song or plume which excites the mating 

 impulse in the hen, is also in so high a proportion of 

 •cases most pleasing to man himself. And not only this, 

 but in their past history, so far as it has been traced {e.g. 

 in the development of the characteristic markings of the 

 male peacock and argus pheasant), such features have 

 gradually become more and more pleasing to us as they 

 have acted as stronger and stronger stimuli to the hen. 

 Why should this be ? . 



In the chapter on nest-building, incubation and 

 migration, there is a most effective reply to those (and 

 they are many) who point to the " coincidence " that 

 " congenital variation on the one hand, and intelligent 

 choice on the other, coincide in direction and tend to 

 the same result," as almost too much to be believed 

 except on the supposition that the latter has through 

 heredity given rise to the former. To this argument the 

 •author replies that both these principles are 



" working, in their different spheres, towards the same 

 •end- that of adaptation. ... Is it a coincidence in any 

 proper sense of the term ? Surely not. If two men start 

 for the same place, the one by sea and the other by land 

 we should not regard it as a coincidence if both got 

 there." 



A number of interesting facts are quoted about bird 

 '.migration, and the author surmises, but very cautiously, 

 that 



•" while the migratory instinct is innate, and perhaps there 

 is an instinctive tendency to start in a given direction, 

 yet the element of traditional guidance may be effectual, 

 in the migratory stream as a whole, in some way that we 

 iiave hitherto been unable to observe " (p. 261). 



The onus of proof seems certainly to rest with those 

 who dispute this latter conclusion, and who hold so in- 

 herently improbable a view as that there is an instinctive 

 knowledge, prior to experience, of geographical routes of 

 enormous length and devious course. A single observ- 

 ation recorded by W. Warde Fowler (in the Midland 

 Naturalist) a few years ago, points very strongly m the 

 opposite direction. Mr. Fowler was standing on the 

 English coast just opposite the western end of the Isle of 

 Wight, but the day was misty and the island mvisible. 

 He watched the successive companies of swallows sweep- 

 ing by eastward to join the migratory stream to the south, 

 and he saw that each company followed the circuitous 

 coast-line leading north of the island. All at once he 

 noticed a change : a company arriving at the spot where 

 he was standing, rose in the air and then flew to sea in an 

 eastward direction. He then turned and saw that the 

 mist had cleared and the island was visible. The birds 

 were now able to take the shorter route, for they could 



see the way. ■ , 1 u- 



With regard to the question "Are acquired habits 



"inherited?" the author in the thirteenth chapter, after a 



keen criticism of the evidence concludes, but with much 



caution, that " there is but little satisfactory and convincing 



-evidence in favour of transmission." The appearances 



NO. 1485, VOL. 57] 



which have suggested an opposite conclusion to many 

 writers are explained in the next chapter, " Modification 

 and Variation." We have here an exposition of a most 

 interesting and useful suggestion independently made by 

 the author, Prof. Osborn of New York, and Prof. Mark 

 Baldwin of Princeton. Others, {e.g. Prof. Weismann) 

 have previously laid more or less stress upon the same 

 principle, but it has been due to the writings and influence 

 of these three authorities that the matter has been put in 

 its true hght, and the principle shown to be an important 

 contribution to organic evolution. This principle, which 

 has been described in America by the not very self-evident 

 term "organic selection," is thus explained by Prof. 

 Lloyd Morgan in the work now referred to. 



" If now it could be shown that, although on selectionist 

 principles there is no transmission of modifications due 

 To individual plasticity, yet these modifications afford the 

 conditions under which variations of like nature are 

 afforded an opportunity of occurring and of making them- 

 selves felt in race progress, a farther step would be taken 

 towards a reconciUation of opposing views. 



A case is then considered : suppose there is a change 

 of environment and the congenital variations are not 

 equal to the occasion, " individual plasticity steps in to save 

 some members of the race from extinction . . . through 

 a modification of the bodily tissues." In this way time 

 is given for the appearance of congenital variations in the 

 same direction, which is therefore rendered possible by 

 the power of individual modification. 



"Thus if the conditions remain constant for many gen- 

 erations, congenital variation will gradually render here- 

 ditary the same strengthening of . •• structure that was 

 provisionally attained by plastic modification The effects 

 ?re precisely the same as they would be if the modifi- 

 cation in question were directly transniitted in a slight 

 but cumulatively increasing degree ; they are reached, 

 however, in a manner which involves no such trans- 

 mission." In this way " we may accept the facts adduced 

 by the transmissionist, and at the same time interpret 

 them as selectionist principles." 



This principle is, in the opinion of the present writer, 

 a valuable aid in the attempt to understand the evolu- 

 tion of the organic world. It should be observed, 

 too, that the author does not intend any part of this 

 principle as a substitute for natural selection ; for he fully 

 recognises that the " innate plasticity » is as much a pro- 

 duct of natural selection as "congenital definiteness 



^The last chapter deals with " Heredity in Man"; and 

 here the author concludes that 



"mental progress is mainly due, not to inherited incre- 

 ments of mental faculty, but to the handing on of the 

 results of human achievement by a vast extension of that 

 which we have seen to be a factor in animal life, namely 

 tradition." 



In his final summary he states that 



"there is little or no evidence of individually acquired 

 habits in man becoming instinctive through heredity. 

 Natural selection becomes more and more subordinate 

 in the social evolution of civilized mankind ; and it would 

 seem probable that with this waning of the influence of 



