May 14, 1891] 



NATURE 



29 



those who were interested in the matter would be able to form 

 their own opinion as to the value of the arguments adduced on 

 either side of the question. I very much regrel to find, how- 

 ever, that Dr. Romanes — whose amount of spare time appears 

 to be most enviably inexhaustible — still finds it necessary to 

 prolong the correspondence. I am compelled, therefore, to enter 

 the field once more, if only for the purpose of presenting my 

 own case in its true light. What Dr. Romanes's position may 

 now be I must confess is becoming distinctly less clear with 

 each of his contributions to the subject, but I am not the first who 

 has lost his way in attempting to thread the mazes of this writer's 

 productions. As far as I am concerned it will suffice to say that 

 the case is not " simply" as he presents it in the foregoing com- 

 munication. In the review of Mr. Pascoe's book, from which this 

 discussion originated, I did not merely reproduce " Mr. Wallace's 

 argument against Mr. Spencer's defence of 'use-inheritance.'" 

 I accepted that argument as valid, but I extended it by em- 

 phasizing the importance of the factor of superimposed useful 

 characters accumulated during successive periods of the phylogeny. 

 I pointed out that large numbers of cases of co-adaptation might 

 be thus accounted for, and I used Mr. Spencer's own illustra- 

 tion by way of example. In summing up his own conclusion, 

 Mr. Wallace says: "The difficulty as to co-adaptation of 

 parts by variation and natural selection appears to me, there- 

 fore, to be a wholly imaginary difficulty which has no place 

 whatever in the operations of Nature" (" Darwinism," p. 418). 

 Not only, therefore, has Dr. Romanes misrepresented my view, 

 but he has gone further. The other "argument on the same 

 side " referred to in the above communication is this very denial 

 of co-adaptation as a fact in Nature. This, with most amazing 

 sangfroid, is now claimed by my correspondent, who speaks of 

 it as " the one which I had stated " ! I must leave it to others 

 to decide what value can be attached to the statements of a 

 writer who adopts the principle of appropriating an argument, 

 and putting it forward in a manner which would lead most 

 readers to consider that he had been the first to elaborate it 

 simply because he has expressed the same idea in abstract 

 symbols instead of in concrete terms. 



The next phase in the discussion is the admission by Dr. 

 Romanes that Mr. Wallace's conclusion is correct, i.e. that co- 

 adaptation is non-existent : " As it appears to me, from his reply, 

 that Prof. Meldola's views on the subject of ' co-adaptation ' 

 are really the same as my own, I write once more in order to 

 point out the identity" (Nature, vol. xliii. p. 582). Mr. 

 Romanes did more, therefore, than simply point out that we 

 were agreed that this was "the only argument which could be 

 properly brought against Mr. Spencer's position." He said 

 that our views were " really the same," and this after I had 

 accepted Mr. W^allace's conclusion as to the non-existence of co- 

 adaptation. To crown all, he now tells us that he has no fully- 

 formed opinion to express, but that he is in a condition of 

 "suspended judgment"! I must really leave the case as it 

 stands. If "neo- Darwinians" have a language of their own, 

 ^at any rate it appears to be intelligible among themselves, if 

 only from the circumstance that they have been enabled to 

 stereotype a phrase which conveys their views with respect 

 to the difficulty of following my correspondent's reasoning. I 

 have been no more fortunate than other " neo-Darwinians " 

 in this attempt, but in the endeavour to carry on the 

 discussion of a biological question with a writer who stops 

 short as soon as the subject assumes a truly biological 

 aspect (see Nature, vol. xliii. p. 582), I have become keenly 

 impressed with the utter sterility of Dr. Romanes's method, 

 which not only fails to advance our knowledge of the 

 origin of species by any substantial contribution of fact, but 

 which degrades the theoretical side of the subject into mere 

 verbiage. If this is " palaeo-Darwinism," I am rejoiced to think 

 that I am grouped with those who are outside the pale. 



In conclusion, to prevent further misunderstanding, let me 

 add that, in admitting that the chances are " infinity to one " 

 against a number of independent tiscful variations occurring 

 when required in the same individual, I merely quoted the ex- 

 pression as given by Mr. Herbert Spencer and repeated by Dr. 

 Romanes. I do not for a moment suppose that Mr. Spencer 

 used the words in any more than a colloquial sense as indicating 

 that there were "heavy odds" against such a combination, and 

 in this sense only is my admission made. That the phrase has 

 no exact mathematical significance is, I imagine, sufficiently 

 obvious, but I have thought it desirable to make this qualifica- 

 tion. R. Meldola. 



NO. 



II 24, VOL. 44] 



Physiological Selection and the Different Meanings 

 given to the Term "Infertility." 



In the discussion concerning the segregation of varieties 

 occupying the same region, and the influence of physiological 

 selection in securing this result, it is necessary that we consider 

 the different meanings given to some of the terms by different 

 writers. The general fact on which Dr. Romanes insisted, in 

 his paper on " Physiological Selection," was compatibility in 

 the reproductive system of some, and incompatibility in that 

 of others belonging to the same species. On p. 360 of his paper 

 we read that "racial incompatibility," "however produced," 

 " is the primary condition required for the development of varie- 

 ties into species." Infertility and sterility are also used by him as 

 equivalents for incompatibility in the reproductive system. Thus, 

 on p. 400 we find the statement that " All natural varieties 

 which have not been otherwise prevented from intercrossing, 

 and which have been allowed to survive long enough to develop 

 any differences worth mentioning, are now found to be protected 

 from intercrossing by the bar of sterility — that is, by a previous 

 change in the reproductive system of the kind which my theory 

 requires." 



Dr. Romanes did not attempt to catalogue the different forms 

 of discriminative incompatibility that are included in the incom- 

 patibilities of the reproductive systems of different races, but 

 reference was made to three forms : (l) to compatibility in the 

 time of flowering in those of the same race, as contrasted with 

 incompatibility in those of difl"erent races, as on pp. 352 and 

 356 ; (2) to greater numerical fertility when the male and female 

 elements of the same race unite, than when those of different 

 races unite, as in the note on p. 354 ; and (3) to numerical in- 

 fertility through deficient production by hybrids, as on p. 369, 

 and p. 357 in the note, and in the suggested experiments on 

 p. 405, in which the pure and hybrid seed are both to be sown, 

 and the comparative "degrees of fertility" to be noted. To 

 these forms which were mentioned, we may add, as coming 

 under the category of physiological incompatibilities, (4) lack 

 of vigour in hybrids ; (5) lack of adaptation in hybrids ; (6) lack 

 of escape from competition with kindred in hybrids ; and (7) the 

 superior energy and promptness with which the male and female 

 elements unite in pure unions, as contrasted with cross unions. 

 Dr. Romanes probably refers to this principle when he speaks 

 of sterility as "failure to blend" (p. 365). 



This last, when associated, with the free distribution of the 

 fertilizing elements, ensures the segregation (that is, the dis- 

 criminative isolation) of two or more varieties occupying the 

 same area and propagating during the same season, and there- 

 fore seems to me the most important of the forms of physio- 

 logical segregation. This segregative principle, which I call 

 potential or prepotential segregation, must, in almost every case, 

 be operative between species and varieties that continue distinct 

 while indiscriminately mingled on the same area and while 

 fertilized by elements freely and indiscriminately distributed 

 during the same season, for no other principle is able to secure 

 free propagation and at the same time to prevent crossing under 

 such conditions. Seasonal segregation is here excluded, and the 

 other forms of physiological segregation when acting under such 

 conditions are of little avail in preventing swamping unless 

 carried to the extreme, and they then involve a waste of from 

 one-half to the whole of the germs of the less numerous variety ; 

 for the most favourable case possible is when two varieties 

 occupy the area in equal numbers, and such cases rarely exist, 

 especially in the initial history of species. 



Though numerical infertility and tardy potency are readily 

 distinguished, complete impotence and complete numerical 

 sterility are more likely to be confounded ; for the complete 

 incapacity of the male and female elements of different varieties 

 for uniting involves failure to produce hybrids, as complete as 

 when the elements unite without producing living offspring or 

 germinating seed. The great difference is that in the case of 

 cross impotence the germ remains unaffected by the alien fer- 

 tilizing element, and therefore ready to be fertilized by any 

 fertilizing element of its own kind that may reach it ; while in 

 the case of simple numerical cross sterility (if there be any such 

 case) the alien elements promptly unite, and therefore leave no 

 opportunity for subsequent fertilization by the coming of the 

 kindred fertilizing elements. Cross impotence, with prepotence 

 of pure unions when associated with the free distribution of the 

 fertilizing elements, produces positive segregation ; for, when 

 characterizing varieties occupying the same area, it ensures the 



