Dec. 9, 1886] 



NA TURE 



'25 



cm see, the fate of the theory of physiological selection. Can no 

 one answer it?" 



This is a question which has arisen out of the theory of 

 physiological selection itself, and, as Mr. Catch pool was the first 

 to propound that thory, I am afraid he will find that no one as 

 yet is able to answer his question. But it may interest some of 

 your readers to know that I have collected a considerable body 

 of facts tending to show that there is a correlation between fer- 

 tility of allied .species and the fact of their living on isolated 

 areas, as well as another correlation between sterility of allied 

 species and the fact of their living on continuous areas. But it 

 seemed to me undesirable to publish these facts until very largely 

 augmented ; and, finding that no observations had been ex- 

 pressly made upon the subject, I read my paper before the 

 Linnean Society for the purpose of inducing naturalists in 

 different narts of the world to try experiments on the fertility of 

 nearly allied species inhabiting isolated areas, as well as to test 

 for degrees of sterility between natural varieties and parent 

 forms on continuous areas. Meanwhile I am myself trying ex- 

 periments on the mutual fertility of isolated species, as well as 

 upon the sterility of natural varieties with parent forms. Where 

 birds and mammals are concerned, I am using the numberless 

 islands of all sizes on the west coast of Scotland, which are 

 admirably suited to the purpose. Any of your reailers in any 

 parts of the world who are acquainted with well-marked natural 

 varieties of birds or mammals which (together with their parent 

 forms) would be likely to thrive on these islands, would greatly 

 oblige me by communicating suggestions. 



I may take this opportunity of also requesting any of your 

 readers who may have further remarks or criticisms to make on 

 the theory of physiological selection not to delay their publica- 

 tion. For it is surely desirable that discussion of the subject 

 "on the high //vo;-; road" should come to an end. Until a 

 large number of experiments shall have been made, any definite 

 judgment upon the theory must be either biassed or premature ; 

 and therefore the only influence that can now be exercised by 

 adverse criticism is that of discouraging the work of verification. 

 On this account, and on this account alone, is it worth one's 

 while to answer such criticism. Hitherto I have waited till it 

 should come to an end, and withdrawn the answer previously 

 referred to in these columns as having been in type for the For!- 

 nightly RndTaK When it has come to an end, I will furnish a 

 general reply in the Nineteenth Century, and shall then hope to 

 show that whatever " fate " may be in store for the theory at the 

 hands of Nature, at all events it is certain that it has been in 

 no way affected by the assault of naturalists. 



George J. Romanes 



Heredity in Abnormal-Toed Cats 

 The calculation made by Mr. J. H. flodd in last week's 

 Nature (p. 53) of the numerical propo tion of the sexes of Mr. 

 Poulton's race of extra-toed cats, in relation to the recurrence of 

 the abnormity, is very interesting as an inferrable deduction from 

 the premises of Mr. Poulton's elaborate tabulation of his obser- 

 vations ; Vmt it is, I think, doubtful whether it is not misleading 

 as a generalisation from the facts collected by him. A conclusion 

 arrived at by means of a mathematical method is too absolute an 

 inference, and not necessarily reliable, when applied to purely 

 biological cases, on account of the numerms intervening factors 

 (perhaps mostly unknown, but yet of importance) which are 

 incapable of being appreciated within such an estimate, and 

 which may, in consequence, invalidate the main point under 

 consideration. This appears to be the case on the present occa- 

 sion ; for Mr. Poulton mentions, in describing the kittens of 

 VHP (p. 39), that by far the most highly specialised develop- 

 ment of the abnormity he has observed, throughout the entire 

 race, was attained in a maU~\\\V' iv. Considering that the 

 large majority of individuals possessing the character are of the 

 9 sex, as pointed out, by Mr. Hodd, this fact is really very 

 striking. But, at the same time, if the point alluded to by Mr. 

 Hodd were considered as amounting to a principle, we should 

 naturally be led to infer that the abnormity might become equiva- 

 lent to a secondary sexual character, which is so improbable that 

 it scarcely bears suggestion. Besides, it is necessary to bear in 

 mind that all the observations carried on as yet liy Mr. Poulton 

 have dealt witli the ? infiitenee alone ; and it may be accounted for 

 by the very reason that all the i s have been carefully eliminated 

 from exercising any influence on the race, that the predominant 

 effect, nnmcrieally, is on the 9 side ; while it is most probable 



that if aa abnormal i were selected (say, the individual just 

 referred to) as a starting-point fir experiment with normal i s, 

 the result would exhibit a general tendency towards superior 

 persistence of the character operating with greater potency 

 amongst the males than the females. It would be very interest- 

 ing to experiment in this manner under the isolation happily 

 promised in the Madeiran Islands. 



Mr. Hodd's statistical statement is, doubtless, correct in the 

 main, under the restricted provision just suggested, only one 

 must not attach too great importance to it. The preponderance 

 in number of the 9 s over i s is, indeed, still more noticeable 

 when the ratio of each sex to the total number of the thirty-six 

 cats is considered. Thus it appears that of twelve i s I3f per 

 cent, are normal, and only 19* per cent, abnormal ; whilst of 

 the twenty-four 9 s igj per cent, are normal, as many as 47* 

 per cent, are abnormal. It is perhaps a little premature to place 

 entire reliance upon so small a number, but it will prove interest- 

 ing to compare the statistics brought out in Mr. l-Iodd's letter 

 with a larger number in time to come. 



In considering such a dose anri carefully detailed analysis as 

 that presented by Mr. Poulton, it is of no little interest to find, 

 on referring to that wealth of facts and principles, " The Descent 

 of Man," tliat these results are in complete accord with, and 

 confirm the law^ of inheritance formulated by Darwin, if the 

 strictures imposed by him, as if in anticipation of future observa- 

 tions, are duly regarded ; and as his remarks apply to the present 

 subject very directly, — although bearing more especially upon 

 sexual selection in general, — I cannot do better than quote some 

 of the more pithy : — " Why certain characters should be in- 

 herited by both sexes, and other characters by one sex alone, 

 namely by that sex in which the character first appeared, is in 

 most cases quite unknown. We cannot even conjecture why 

 with certain sub-breeds of the pigeon, black stride, though trans- 

 mitted through the female, should be developed in the male 

 alone, whilst every other character is equally transferred to both 

 sexes ; why, again, with cats, the tortoiseshell colour should, 

 with rare exceptions, be developed in the female alone " (" De- 

 scent," 2nd ed., p. 232). It is curious that the cats under obser- 

 vation happen to be tabby-tortoiseshell, and the remark made by 

 Darwin (p. 230), that "as a rule it is the females alone in cats 

 which are tortoiseshell, the corresponding colour in the males 

 being rusty red," fully obtains in the present case, since the i s 

 are, unless tabby, sandy-coloured, but never tortoiseshell. It i.s 

 furthermore important to notice that the sandy individuals have 

 the supernumerary digits as fully developed as any of the 9 s in 

 the same Utter. 



Darwin's explanation of the persistence of abnormal characters 

 is on the lines of the theory of pangenesis, as follows : — 



" It is in itself probable that any character .appearing at an 

 early age would tend to be inherited equally by both sexes, for 

 the sexes do nit diff r much in constitution before the power of 

 reproduction is gained. On the other hand, after this power has 

 been gained, and the sexes have come to differ in constitution, 

 the gemmules (if I may again use the language of pangenesis), 

 which are caxt oft' from e.ich varying part of the one sex, would 

 be much more likely to possess the proper affinities for uniting 

 with the tissues of the same sex, and thus becoming developed, 

 than in the other sex " (p. 232). On p. 237 we find the 

 further remark :— "The presence of supernumerary digits, and 

 the absence of certain phalanges, must be determined at an early 

 embryonic period, .... yet these peculiarities, and other 

 similar ones, are often limited in their transmission to one sex : 

 so that the rule that characters developed at an early period 

 tend to be transmitted to both sexes here wholly fails." ^ 



And, in conclusion : — " Characters of the parents often, or even 

 generally, tend to become developed in the offspring of the same 

 "sex, at the same age, .... in which they first appeared in the 

 parents. But these rules, oiuitif; to unknown causes, are far from 

 heini; ftxeJ. Hence, during the modification of a species, the 

 successive change; inay readily be transmitted in different ways ; 

 some to one sex, and some to both ; some to the offspring at one 

 age, and .some to the offspring at all ages. Not only are the 

 laws of inheritance extremely complex, hut so are the causes 

 which induce and govern variability " (p. 240). 



It is quite remarkable, though it is not at all surprising, how 

 closely Mr. Poulton's facts fit into these deductions of Darwin's, 

 drawn, as they were, from such few instances that they seem to 

 be little less than preconceived ideas. 



But, as it may be due to a one-sided influence in special 

 ' This i? a point which perhaps requires further evidence. 



