Oct. lo, 1889] 



NATURE 



569 



put forward, as it was by Mr. Darwin. It is true that we 

 know little about the physical basis of correlated variation, 

 and are therefore open to hostile criticism when we take 

 refuge in an appeal to it as an explanation of phenomena. 

 The truth is that correlated variation is as important a 

 property of living matter a? heredity and variability them- 

 selves. It may be formulated thus : " Every departure 

 from the parental form of any given part of an animal 

 or plant is accompanied by a definitely correlated and 

 often a commensurate departure in other parts remote 

 from it.'' The possibilities thus introduced are simply 

 gigantic — a new factor is brought in which extends the 

 results of simple variation and selection indefinitely. In 

 the future the laws and limitations of correlated variation 

 will no doubt be determined. At present our knowledge 

 of them rests where Mr. Darwin himself placed it. Both 

 ^Ir. Gulick's doctrine of persistent hereditary tendency, 

 and that of the immense capacities of correlation in 

 variation, commend themselves to the mind of a labora- 

 tory naturalist who is accustomed to conceive of vital 

 phenomena as mechanico-physical affections of a living 

 substance, viz. protoplasm. They are, on the other hand, 

 less valued — perhaps insufficiently — by Mr. Wallace. 



In his chapter on the infertility of crosses, Mr. Wallace 

 treats at length and with admirable effect a very important 

 subject, as to which he is full of ingenious novel sugges- 

 tions and apposite facts. His criticism of Mr. Romanes's 

 essay, entitled " Physiological Selection," appears to me 

 to be entirely destructive of what was novel in that 

 laborious attack upon Darwin's theory of the origin of 

 species. 



The chapter on the origin and uses of colour in animals 

 is that which will be most interesting to the general reader, 

 and is indeed a charming essay, illustrated by numerous 

 woodcuts. Here Mr. Wallace sets forth at length his con- 

 vincing argument as to the use of colour as a means 

 of recognition among animals, giving many examples — 

 amongst others, that of the white patch on the rabbit's 

 tail. In conjunction with his theory of the importance of 

 the principle " like to like " in the segregation of varieties 

 and the consequent development of new species, great 

 significance must be attached both to the nervous 

 organization, which makes recognition possible, and to the 

 markings or other characters which are recognized. A 

 very interesting discussion of Mr. Darwin's theory of 

 sexual selection occurs in a subsequent chapter. Mr. 

 Wallace, whilst admitting some of the effects of sexual 

 selection recognized by Darwin, is not able to follow him 

 in attributing to it the brilliant colours of birds and 

 butterflies. Mr. Wallace attributes the deeper or more 

 intense colouring of the male, which often occurs, to his 

 " greater vigour and excitability." The female in many 

 groups retains the primitive and more sober colours of 

 the group for purposes of protection. The occurrence of 

 colour itself in patches and lines is attributed by Mr. \ 

 Wallace (following the late Mr. Alfred Tylor) to the dis- i 

 tribution of subjacent nerves and blood-vessels, which 

 follow, like the colour-patches, in the main, certain lines 

 determined by the general structure. Mr. Wallace seems 

 scarcely to have succeeded in showing that Darwin's 

 theory of sexual selection is inapplicable to the explana- 

 tion of special developments of colour and ornament, 

 although he has suggested additional causes which 



influence the primary distribution and development of 

 colour. 



We have not space to speak of subsequent chapters on 

 colour in plants and on geographical distribution, con- 

 cerning the latter of which subjects Mr. Wallace speaks 

 with every title to respect, and suggests some novel views. 

 On the " Geological Evidences of Evolution " as well as on 

 the " Fundamental Problems " of variation and heredity, 

 he is less satisfactory. In regard to the latter, one 

 chapter is altogether an inadequate space in which to 

 deal with such an array of antagonists as Mr. Herbert 

 Spencer, Dr. Cope, Dr. Karl Semper, and Mr. Patrick 

 Geddes. Mr. Wallace has barely space to do more than 

 state his opponents' views, and to give a rapid summary 

 of reasons for his dissent, without sufficiently establish- 

 ing those reasons. This will be especially regretted by 

 those who, like myself, agree with Mr. Wallace in his 

 rejection of Spencer's and Semper's Lamarckism, and 

 are unable to attach any serious value to the speculations 

 put forward on this matter by Dr. Cope and Mr. Geddes. 

 The translation of Weismann's " Essays," which appeared 

 coincidently with Mr. Wallace's book — although many of 

 the essays have been for some years familiar to readers of 

 German— supplies that more solid treatment of the sub- 

 ject which is desirable. It is satisfactory to find that 

 justice is done by Mr. Wallace to Mr. Francis Galton, 

 whose views on heredity, arrived at by a special method 

 of inquiry, are closely similar to those arrived at on other 

 grounds by Weismann. 



Prof Semper's work " On the Natural Conditions of 

 Existence as they affect Animal Life" is duly mentioned 

 by Mr. Wallace, and he does not fail to notice the 

 striking fact that in this interesting volume the author 

 entirely fails— as I pointed out in Nature when it 

 appeared — to adduce a single fact in proof of the 

 Lamarckian theory which he sets out to champion. 



Of the American evolutionists Mr. Wallace justly says : 

 " In place of the well-established and admitted laws 

 to which Mr. Darwin appeals, they have introduced 

 theoretical conceptions which have not yet been tested 

 by experiments or facts, as well as metaphysical 

 conceptions which are incapable of proof." They 

 have, in fact, conspicuously abandoned the " scientific 

 method." 



The words which Mr. Wallace has applied to the 

 American evolutionists are, in the opinion of many, 

 strangely applicable to portions of his own concluding 

 chapter on " Darwinism applied to Man." He here 

 introduces us to a " spiritual world" and to "different 

 degrees of spiritual influx." Mr. Wallace is in the pe- 

 culiar position of one who believes that he has ex- 

 perimental evidence of the remarkable theoretical and 

 metaphysical conceptions which he introduces. He 

 boldly takes up this position, and we may be sure 

 that he would not wish attention to be diverted from 

 it. It remains an interesting problem for the future 

 student of human faculty to reconcile Mr. Wallace's 

 wonderful ingenuity and skill as a reasoner and observer 

 concerning animal life, with his views as to the so-called 

 " manifestations " of spiritualists. 



Mr. Wallace's contention that the mathematical, 

 musical, and artistic faculties of man have not 

 been developed under the lav* of natural selection 



