NATURE 



477 



THURSDAY, MARCH 27, 1879 



ORGANISATION AND INTELLIGENCE 



Habit and hitelligence : a Series of Essays on the Laws 

 of Life and Mind. By Joseph John Murphy. Second 

 Edition, iUustrated, thoroughly revised, and mostly 

 rewritten. (London: Macmillan and Co., 1879.) 



Life and Habit. By Samuel Butler. (London : Triibner 

 and Co., 1878.) 



THE first edition of Mr. Murphy's work was reviewed 

 in Nature, vol. i. pp. 288 and 315, a little more 

 than nine years ago, and on reading the article we find 

 little or nothing in the remarks and criticisms then made 

 which require modification on account of subsequent dis- 

 coveries. The present work is, however, ver>' largely 

 new, about one-third of the matter in the first edition, 

 which treated of physical questions, being omitted, and 

 replaced by a series of new chapters on biological sub- 

 jects. It is to these new chapters that we shall mainly 

 confine our present notice. 



Chapter XI. gives a very good summary of the facts of 

 variation from Darwin's " Domestication of Animals and 

 Plants," and other works ; and in Chapter XII. we have 

 these facts discussed in regard to the sufficiency of natu- 

 ral selection for the origin of species. The greatest use 

 is here made of the argument (said to be Prof. Tait's) in 

 the North British Review (June, 1877), and which an- 

 other writer has summed up as follows.: — " The final 

 establishment of the superior type is dependent at each 

 step upon three accidents. First, the accident of an 

 individual sort or variety better adapted to thesurround- 

 ing conditions than the then prevailing type ; secondly, 

 the accident that this superior animal escapes destruction 

 before it has time to transmit its qualities ; and thirdly, 

 the accident that it breeds with another specimen good 

 enough not to neutralise the superior qualities of its 

 mate." Put in this way, the difficulty staggers most per- 

 sons who are not practical naturalists ; yet it has always 

 seemed to me to be really beside the question, and by no 

 means of the importance which Mr. Darwin himself has 

 given to it by acknowledging that the argument had not 

 occurred to him. Even acute \vriters like Mr. Murphy do 

 not see that individual variations or "sports" are of no 

 importance whatever to the theory of natural selection, 

 or he would never bring forward the argument at p. 380, 

 that with an animal born of two parents " there is an 

 .ilmost overwhelming probability that the favourable 

 variation is found only in one," and will therefore 

 diminish in each succeeding generation till it disappears, 

 unless the same favourable variation recurs again and 

 again to counteract this tendency. In what may be 

 termed normal variation, however (which Mr. Darwin 

 has always considered the main agent in supplying mate- 

 rials for natural selection), none of these difficulties occur, 

 and as it is very important to make this clear, I will give 

 a few illustrations of it. There is no part, organ, or 

 character of an animal or plant but what is sometimes 

 more sometimes less developed in different individuals. 

 The whole population of a species in any given year may 

 therefore be divided into two equal portions, with regard 

 to any such organ or character — the less developed and 

 Vol. XIX. — No. 491 



the more developed. Thus, for example, all the foxes of 

 the species Canis vulpes are necessarily divisible into 

 a lighter and a darker coloured group ; into a longer 

 and a shorter tailed group ; into a fleeter and a less 

 fleet group ; into a group with more developed and 

 less developed canine teeth ; and so on with regard to 

 every character, external and internal. This can only be 

 denied by asserting that there are characters which in 

 the species in question are absolutely unvaryittg, an 

 assertion which I am not aware that any one has made 

 or attempted to prove, while it is certainly contradicted 

 by the observations of all who have ever studied nature. 



But if so, what happens when changed conditions occur, 

 rendering the increased development of some faculty or 

 organ beneficial ? Can any one doubt that the one or 

 five, or twenty per cent, of individuals which annually 

 survive will belong, wholly or almost wholly, to the moiety 

 in which that organ or faculty is better developed rather 

 than to that in which it is worse developed ? It matters 

 not at all whether the tnost perfect individual or the 

 twenty most perfect individuals survive or not ; but the 

 survivors will certainly be found among the better adapted 

 rather than among the worse adapted half, and most 

 likely will include a majority of individuals in the better 

 half of the better half. And this process will be repeated 

 every year without fail. There is thus no waiting for 

 favourable variations to occur ; no series of coincident 

 improbable accidents is required ; but the process goes 

 on continuously with ever increasing power owing to the 

 influence of heredity, till the species is modified up to the 

 requirements of the changed conditions. By this process, 

 leading to a decided advance every year, we can quite 

 understand how any dominant species (that is, one which 

 occupies a wide area and has a large population) may be 

 modified quite as rapidly as is required by all ordinary' 

 changes of conditions, although extraordinary changes 

 may lead to the extinction even of dominant species. It 

 is hardly possible to conceive any improvement or modi- 

 fication of a species which might not be brought about 

 by so powerful a selection as this, acting on variations 

 which seem to us very trivial ; while, on the other hand, 

 the effect of greater individual variations or "sports" is 

 verj' uncertain, and may perhaps never be used in nature 

 as a means of modifying species. 



These considerations also show the true bearing of 

 "Delboeuf's Law," to which Mr. Murphy attaches much 

 importance. It is proved mathematically that if, in any 

 species, several individuals are in every generation bom 

 with any particular variation which is neither beneficial 

 nor injurious to its possessors, and if the effect of the 

 variation is not counteracted by reversion, the proportion 

 of the new variety to the original form will constantly 

 increase until it approaches indefinitely near to equality. 

 But as, in every species, there are not one only, but hun- 

 dreds of distinct variations in everj- generation, all sub- 

 ject to change in amount and direction in each succeeding 

 generation, and as each of these will by the above law 

 tend to equality with all others, the rssult must be that 

 every slight recurrent variation will maintain itself in the 

 species on terms of approximate equality with all other 

 variations ; and this will evidently be useful, by keeping 

 up a vast stock of slightly varied forms within the species, 

 which will be ready at any moment to furnish the material 



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