6oo 



NA TURE 



[April 26, 1894 



And he strenuously maintained that a merely passive cessation 

 of selection could not be a cause of degeneration in any degree 

 at all. After a prolonged discussion, however, he allowed that 

 it must be a cause of degeneration to the extent of reducing the 

 previous "survival-mean" to the "birth-mean," but no further. 

 In adopting this view, Prof. Lloyd Morgan estimated that "the 

 amount of degeneration thus produced " might be set down at 

 5 per cent. More recently still Mr. Herbert Spencer, in the 

 Contemporary Review, took the same points of exception to my 

 Cessation of Selection as Prof. Ray Lankester had originally 

 taken—-? e. that it was not the same doctrine as Weismann's 

 Panmixia (the latter being in Mr. Spencer's understanding of 

 it the active reversal of selection due to Economy of Nutrition, 

 &c. ), and that it could not be, in any circumstances or in any 

 degree, a cause of degeneration. 



Both these points, however, were soon settled, as far as the 

 question of Weismann's opinion was concerned, by his replying 

 to Mr. Spencer that the doctrine of Panmixia was identical with 

 that of the Cessation of Selection, and also that in his opinion 

 the principle was not merely a cause of degeneration, but, as a 

 general rule, the sole cause. Moreover, he has repeatedly stated 

 that in his opinion " the amount of degeneration thus produced " 

 is unlimited, so that any organ which has fallen under the influ- 

 ence of Panmixia may, by such influence alone, be reduced to a 

 "vestige," and finally abolished altogether. Thereupon Mr. 

 Spencer, like his predecessors, put the question — What is there 

 in the state of Panmixia that determines a numerical excess of 

 minus over plus variations, such as must be supposed if the 

 amount of degeneration due to Panmixia alone is to proceed 

 further than the survival-mean falling to the birth-mean ? Now 

 this very pertinent question has never been answered by Prof. 

 Weismann. He has simply taken it as self-evident, that when 

 the maintaining influence of selection is withdrawn as regards 

 any organ (owing to the latter having ceased to be useful) atrophy 

 of that organ must ensue in successive generations, and this to 

 an unlimited extent. Therefore I am unable to say what his 

 views upon this important point may be. But in answering Mr. 

 Spencer I gave what my own views have always been with 

 regard to it. I hold that there are at least three very good reasons 

 why, as soon as selection is withdrawn from an organ, the 

 7nimis variations of that organ outnumber the plus variations, 

 and therefore that it must dwindle in successive generations. 

 These three reasons are as follows : — 



(1) The survival-mean must descend to the birth-mean. 

 This is now on all hands acknowledged. But it will only pro- 

 duce, at the outside, 5 per cent, of dwindling. 



(2) Atavism is always at work in our domesticated varieties ; 

 and although there is no evidence to show (as is generally 

 assumed) that but for artificial selection this would in time cause 

 any domesticated variety to revert to its wild type, there is 

 abundant evidence to show that the cessation of such selection 

 is soon followed by deterioration of the artificial type — i.e. 

 degeneration to a very much greater amount than can be 

 explained by the cause above mentioned (i). And, notwith- 

 standing that atavism in the case of specific characters is less 

 pronounced than it is in that of domesticated varieties (owing 

 presumably to their having been much longer inherited), still 

 we know that even here its occurrence is neither rare nor insig- 

 nificant. And it seems evident that in whatever degree it does 

 occur in the case of any specific character, in that degree it must 

 determine a preponderance of niinus over plus variations— at 

 any rate through 10 to 20 per cent, of degeneration. So long 

 as the character is of use to its possessor, natural selection will 

 suppress these atavistic {minus) variations. But when the 

 character ceases to be of use, natural selection will be withdrawn 

 as regards that character, and the resulting preponderance of 

 minus variations due to atavism will lead to degeneration — more 

 slowly, no doubt, than in the case of our domesticated produc- 

 tions, but still, and eventually, to some amount considerably 

 more than that contemplated by the English naturalists who 

 object to the doctrine of Panmixia (i). Hence, it appears to 

 me, these naturalists must have overlooked the necessary presence 

 of this factor under a state of Panmixia — at all events in the 

 earlier stages of degeneration, or before atavism begins to cut 

 both ways. 



(3) As long as an organ or structure is under the influence of 

 natural sehction, any failures in the perfection of hereditary 

 transmission will be weeded out. But as soon as natural selec- 

 tion ceases with regard to this organ or structure, all such im- 

 perfections will be allowed to survive, and, just as in the case of 



NO. 1278, VOL. 49J 



atavistic variations, will act as a dead weight on the side of 

 degeneration. Be it observed, degeneration may occur either 

 in regard to size (dwindling of bulk) or to structure (disorgani- 

 sation of machinery) ; and it is in the latter case that the pre- 

 sent cause of degeneration under a state of Panmixia is pre- 

 sumably of most importance. Thus, for example, we can 

 understand why some of the blind Crustacea in dark caves should 

 have lost their eyes, while they have not yet lost their eye-stalks. 

 The latter, although of larger bulk than the eyes can have 

 been, are of much less complexity in regard to structure. 



These, then, are my reasons for holding that there is no 

 "error" attaching to Weismann's theory of Panmixia as a 

 cause of degeneration, and, so far, no one has attempted to 

 show that there is any error attaching to these reasons. It 

 seems to me desirable that either Mr. Wallace or some of the 

 English naturalists who think with him should now do so, if 

 only for the sake of seeing what Prof. Weismann may have to 

 say upon the whole subject a week or two hence. But I write 

 in no spirit of controversy. I merely ask for information as to 

 what is the "error" into which both he and I are said to 

 have fallen. 



There are certain other points of comparative detail connected 

 with the theory of Panmixia as to which, owing to his reticence, 

 I am uncertain whether Prof. Weismann is in agreement with 

 me. But it seems unnecessary to go into them on the present 

 occasion. For they refer to degeneration by Panmixia below 10 

 to 20 per cent, of dwindling, and the importance of the 

 doctrine lies in the fact of its destroying the direct evidence of 

 the inherited efi"ects of disuse on which Darwin relied in the 

 case of domesticated animals, where, as he showed, there is 

 no Economy of Growth or Reversal of Selection, to account for 

 the 10 to 20 per cent, which their disused organs have under- 

 gone. Hence, one can understand why the doctrine should be 

 obnoxious to Lamarckians, but not why such should be the case 

 with those who disbelieve in the transmission of acquired 

 characters. Prof. Weismann may well ask these naturalists 

 what cause, other than Panmixia, they have to suggest whereby 

 to supplant Darwin's explanation of these particular cases of 

 degeneration. George J. Romanes, 



Hyeres, France, April 16. 



The Late Mr. Pengelly, F.R.S., and the Age of th& 

 Bovey Lignite. 



Having enjoyed the inestimable privilege of the acquaintance, 

 and latterly of the friendship, of the late Mr. Pengelly, for 

 nearly forty years, I ask permission to make a few remarks on> 

 Mr. Starkie Gardner's letter on the Bovey beds, which appears 

 in your issue of the 12th inst. (Nature, vol. xlix. p. 554). 



From the year 1878 to 1885 Mr. Pengelly published an annual 

 paper in the Trans. Dev. Assoc, entitled " Notes on Slips con- 

 nected with Devonshire." It was a pillory of which the writer 

 stood in wholesome dread, and which by the utmost care he 

 succeeded in escaping. Had Mr. Gardner's letter appeared 

 within the years named, its author would not have been so 

 fortunate. 



Mr. Gardner, in lightly attributing one slip to Mr. Pengelly, 

 himself stumbles thrice. 



Mr. Gardner, speaking of the Bovey beds, says (for the sake 

 of clearness his remarks are quoted in italics) : — 



(1) " They are, however, not laciest rine but Jluviatilc, con- 

 sisting of cuj-rent-bedded coarse grits alternating- with lignitic 

 muds." Now, according to Pengelly, the beds from the second 

 to twenty-seventh were composed of sand, clay, and lignite ; 

 whereas all below the twenty-seventh consisted of clay and 

 lignite only ; of these latter beds there were forty-five. Among 

 these occurred not even sand, to say nothing of coarse grits. 



(2) ^^ Neither are they Miocene." This caution might lead 

 some of your readers to infer that Mr. Pengelly considered that 

 the beds referred to were Miocene. He, however, carefully 

 avoided defining the horizon of the beds in his paper thereon, 

 his title being, "On the Correlation of the Lignite Formation 

 of Bovey Tracey, Devonshire, with the Hempstead beds of the 

 Isle of Wight." 



On this question of age Mr. Pengelly wrote: — "The 

 question it will be seen is simply one of classification. It in 

 no way affects the contemporaneity of the formations which 

 have been spoken of, and which are, all Lower Miocene, or, all 

 Upper Eocene ; for they must certainly go together." 



(3) ^^ In determining the age of the deposits, great stress zoas 



