No. 1070, Vol. 42] 



NATURE 



I 



antiquity of man, primaeval man, and ancient lake- 

 dwellings. The section on " Protoplasm " includes papers 

 on the origin of life, the basis of life, bacteria, disease 

 germs, and fermentation. Under " Colour " we find articles 

 on the colour of flowers, the colour of animals, and warning 

 colours and mimicry. " Movement " takes in essays on 

 movements in plants, the sleep of plants, climbing plants, 

 and carnivorous plants. Discussing so many subjects, 

 the writer is, of course, obliged to content himself with 

 the statement of very wide views ; but his expositions 

 are so clear and fresh that the book ought to be of 

 considerable service to the readers to whom he specially 

 appeals. It will give them at least a general conception 

 of the nature and direction of some of the lines of 

 modern research, and may induce them to seek elsewhere 

 for fuller knowledge. 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications. ^ 



Panmixia. 



I REGRET that I was led to doubt the sincerity of Mr. Romanes 

 when he professed to have formed the conclusion that my words 

 meant the reverse of their plain significance. I had not sup- 

 posed that there was any one capable of making such a mistake. 



I should be glad to terminate this discussion by a brief state- 

 ment of the divergence of view between Mr. Romanes and myself 

 as to the original matter in question, from which Mr. Romanes 

 has led the correspondence by raising a variety of collateral 

 issues. At the same time I should like to take the opportunity 

 of saying what I believe Mr. Romanes would reciprocate, viz. 

 that there is no ill-feeling but only a divergence of opinion 

 between us. 



Mr. Romanes definitely states that when an organ has become 

 useless it will decrease in successive generations as a result of 

 " cessation of selection " to about half its original size, without 

 the co-operation of any such cause as economy of growth. He 

 has repeated in effect this statement in his last letter. The result 

 attributed by him to mere cessation of selection is, it must be 

 noted (because he shows a tendency to waver and to substitute 

 "degeneration" for "decrease in size"), z. decrease of size : a 

 mere failure in the exact adjustment of the parts of a complex 

 organ is nH the result in question. Of this I have a few words 

 more to say below. 



Mr. Romanes not only attributes the decrease in size of a 

 useless organ to the cessation of selection pure and simple, but 

 he calls that condition " a causal principle," and claims to have 

 discovered it,^ He has also stated that, whilst (to use his own 

 words) "inherited decrease" of an organ must be due to this 

 principle, it is "remarkably strange" that Mr. Darwin had 

 overlooked it, and that it was unfortunate that he (Mr. Romanes) 

 only gained the idea of this novel principle just after the appear- 

 ance of the last edition of the " Origin of Species." 



On the other hand, I consider that Mr. Romanes, by these 

 contentions, obscures the theory of organic evolution, and that 

 he presumes to censure Mr. Darwin without cause. There is 

 nothing unfortunate in the date of Mr. Romanes's idea, because 

 the idea is entirely erroneous ; and it was no strange oversight of 

 Mr. Darwin not to attribute the decrease of useless parts to " the 

 principle of cessation of selection," or, in other words, to their 

 uselessness alone — for the simple reason that he would have 

 made a blunder had he done so. It is this blunder which Mr. 

 Romanes places before us as his own contribution to the theory 

 of panmixia : it is this blunder which Mr. Darwin not only did 

 not make, but rendered almost impossible for others by his 

 discussion of the matter ("Origin of Species," p. 401). 



It is an incontrovertible mathematical fact that the only ej^ect of 

 promiscuous breeding or panmixia (considered apart from all other 

 influences) upon an organ or part which presents variations round 



' The erection of a negative condition — a cessation— into the position of a 

 causal principle is an artifice which is very likely to obscure the view of the 

 related facts. The " causal principle of non-existence" and "the reversal 

 of being," would be worthy of the author of the artifice who professes also 

 to have extracted an essence from an idea — the idea of promiscuous breeding, 



an average mean unl/ be to increase the number of individuals near 

 the average mean, in proportion to the number of generations in 

 which the panmixia is operative. The notion that the hap- 

 hazard inlerbreeding of "variations about a mean," must by 

 itself lead to a shifting of the mean in the direction of diminished 

 size — without the assistance of any special cause favouring 

 reduction in size — is, to put it plainly, absurd. 



It is, I believe, a mi take on the part of Mr. Romanes to say 

 that Gallon, Weismann, and Poulton agree with him in this 

 astonishing fancy. But, were this the case, the mathematical 

 fact would remain as it \'. 



Given a race of organisms in which a part has become useless, 

 it is only (as Mr. Darwin pointed out) when some cause (such as 

 economy of growth) favouring diminished size is operative, that 

 the average mean of the size of the part will in successive gene- 

 rations shift in the direction of decrease. Mr. Darwin saw this, 

 and explained it. Mr. Romanes not only failed to appreciate 

 the considerations advanced by Darwin, but actually ilow 

 charges him with oversight for not having made the blunder 

 which he carefully avoided. 



In conclusion, I have a few words to say in regard to the 

 possibility of an organ consisting of several nicely adjusted parts 

 losing that adjustment in a state of panmixia without the co- 

 operation of economy of growth. Mr. Romanes erroneously 

 declares that if we admit this we must also admit that decrease 

 in size must similarly result. I am not surprised to find that he 

 thinks so, and do not doubt his sincerity. But really the two 

 cases present very different problems. Suppose the organ in 

 question to be represented by fifty independent variables ; then 

 we have to consider not the probability of the average mean 

 of each kind of variable being maintained but the probability 

 of the production of the necessary combinations of fifty of them 

 with the specific initial proportions of each of the fifty elements. 

 Whether it is or is not probable that the complex adjustment 

 and interaction of parts would be maintained in the absence of 

 all interfering causes in a state of panmixia is a difficult question. 

 It is one which is hardly worth further discussion, since it is im- 

 possible that the results of panmixia without such interfering 

 causes should ever present themselves in organic nature. 



It is,' moreover, quite certain that any conclusion we may 

 adopt in regard to that matter will not alter the mathematical 

 fact that, given a numerous race and a long series of generations, 

 the average mean round which the variations in size of a useless 

 organ are distributed will not ultimately shift in the smallest 

 degree either towards increase or decrease of size, as the result 

 of the promiscuous interbreeding of the variations. 



April 26, E, Ray Lankester, 



The Inheritance of Acquired Characters.- 

 It surprises me to find that anyone who has looked into the 

 evidence can doubt that acquired characters, as distinct from 

 congenital ones, may, like congenital characters, become heredi- 

 tary, and produce physiological effects. The instance men- 

 tioned in Herbert Spencer's letter in Nature (vol. xli. p. 

 511), of domestic varieties of animals losing the power of erect- 

 ing the ears, appears as nearly conclusive on the subject as such 

 an instance can be. 



On the habits or instincts of domesticated varieties, Darwin 

 says: — "It may be doubted whether anyone would have 

 thought of training a dog to point, had not some one dog 

 naturally shown a tendency in this line. . , . When the first 

 tendency to point was once displayed, methodical selection and 

 the inherited effects of compulsory training in each successive 

 generation would soon complete the work" ("Origin of 

 Species," 4th edition, p. 256), 



I quote another instance from Carpenter's "Comparative 

 Physiology" (p, 987) :— " Sir C. Lyell mentions that some 

 Englishmen, engaged in conducting the operations of the Real 

 del Monte Company in Mexico, carried out with them some 

 greyhounds of the best breed to hunt the hares which abound 

 in that country. It was found that the greyhounds could not 

 support the fatigues of a long chase in this attenuated atmo- 

 sphere, and before they could come up with their prey they lay 

 down gasping for breath ; but these same animals have pro- 

 duced whelps which have grown up, and are not in the least 

 degree incommoded by the want of density in the air, but run 

 down the hares with as much ease as do the fleetest of their 

 race in this country," 



Mr, Gulick's letter in Nature (vol. xli. p. 536), in- 

 sisting that the first and only absolutely essential factor in the 



