April 17, 1890] 



NATURE 



559 



•criticizing Weismann upon what he calls " reversal of selection," 

 which he now tells us is the same principle as " economy of 

 growth." Yet in the earlier letter he entirely omits to credit Mr. 

 Darwin with the recognition of that principle, and after carefully 

 asserting that Mr. Darwin had overlooked the principle of 

 " panmixia," he gives in an historical form what he (Mr.Romanes) 

 had argued some years ago, and what his views were — including 

 herein the principle of economy of growth, or more generally, 

 reversed selection. Now that the oversight has been pointed 

 out to him Mr. Romanes allows that "it is a matter of familiar 

 knowledge that Mr. Darwin at all times, and through all his 

 works, laid considerable stress upon the economy of growth (or 

 more generally, reversed selection)." 



Mr. Romanes makes an unreal separation between " cessa- 

 tion of selection " and "reversal of selection " ; at the same 

 time, for the mere purpose of badinage, he affects to suppose 

 that I do not perceive any difference between them — a suppo- 

 sition which cannot be sincere in view of the statements in my 

 letter of March 27. Cessation of selection is not a " principle " 

 at all. It is a condition which alone cannot produce any im- 

 portant result. At the same time, what Mr. Romanes mislead- 

 ingly calls "reversal of selection," viz. "economy of growth," 

 cannot become operative in causing the dwindling of an organ 

 until the condition of " cessation of selection " exists. The fact 

 is — as Mr. Romanes insisted before it was pointed out in these 

 pages that it was no new principle of his own discovery, and 

 when he wished to lay claim to an improvement upon Weis- 

 mann's exposition of "panmixia" — cessation of selection must 

 be supplemented by economy of growth in order to produce the 

 results attributed to "panmixia." And inasmuch as economy 

 of growth as a cause of degeneration involves the condition of 

 cessation of selection, Mr. Darwin, in recognizing the one 

 recognized the other. 



By the use of the term " the principle of the cessation of 

 selection " Mr. Romanes has created an unnecessary obscurity. 

 To say that a part has become "useless," or "has ceased 

 to be useful to its possessor" as Mr. Darwin does, is clearly the 

 same thing as to say that it " has ceased to be selected " — selec- 

 tion and use being inseparable. Mr. Darwin states that such 

 parts " may well be variable, for their variations can no longer 

 be checked by natural selection." That is panmixia. It is 

 true that Mr. Darwin did not recognize that such unrestricted 

 variation must lead to a diminution in size of the varying part 

 without the operation of the principle of "economy of 

 growth." This was no strange oversight : he would have been 

 in error had he done so. On the other hand, he did recognize 

 that, given the operation of that principle, the result would 

 amount to the dwindling and degeneration of parts which are 

 referred to as rudimentary. 



" Panmixia " as a term clearly refers to the unrestricted inter- 

 breeding of all varieties which may arise, when selection in 

 regard to a given part or organ is no longer operative. The 

 term, like its correlative "cessation of selection," does not 

 indicate a principle but a natural condition : it does not involve 

 the inference that a dwindling in the size of the organ must 

 result from the inter-breeding ; but simply points to a precedent 

 condition. 



I am by no means prepared to admit that pinmixia alone 

 {i.e. without economy of growth or other such factors) can be 

 relied upon, 2% it is by Mr. Romanes, to explain the reduction in 

 size of the disused organs of domesticated animals. I observe 

 that in his letter on this subject to Nature of April 9, 1874, 

 Mr. Romanes does not attempt to attribute a dwindling action 

 to " panmixia " alone, but assumes a limitation by economy of 

 growth to any increase beyond the initial size of the organ which 

 has become useless. Given this limitation and the condition of 

 panmixia, the dwindling follows ; but it is absurd to attribute 

 the result, or any proportion of it, to the panmixia or cessation 

 of selection alone. On the other hand, when we consider shape 

 and structure, and not merely size, it is clear that panmixia 

 without economy of growth would lead to a complete loss of that 

 complex adjustment of parts which many organs exhibit, and 

 consequently to degeneration without loss of bulk. That the 

 principle of economy of growth is ever totally inoperative has 

 not been demonstrated. E. Ray Lankes ter. 



April 9. 



Heredity, and the Effects of Use and Disuse. 

 All biologists will, I am sure, agree as to the desirability of a 

 thorough testing of the hypotheses relative to the inheritance of 



the effects of use and disuse. As Mr. Spencer says, in the pre- 

 face to " The Factors of Organic Evolution," "Considering the 

 width and depth of the effects which acceptance of one or other 

 of these hypotheses must have on our views of Life, Mind, 

 Morals, and Politics, the question — Which of them is true ? de- 

 mands, beyond all other questions whatever, the attention of 

 scientific men." 



As experiments suggested by those who believe in the in- 

 herhance of the effects of use and disuse would hardly carry the 

 weight to those who do not believe in this inheritance which ex- 

 periments proposed by themselves would, I write to suggest 

 the desirability of undertaking an investigation which, Prof. 

 Weismann thinks, would prove one or other hypothesis. He 

 states it in the following words on p. 90 of the English edition 

 of his " Essays" : — 



"If it is desired to prove that use and disuse produce 

 hereditary effects without the assistance of natural selection, it 

 will be necessary to domesticate wild animals (for example, the 

 wild duck), and preserve all their descendants, thus excluding 

 the operation of natural selection. If, then, all individuals of 

 the second, third, fourth, and later generations of these tame 

 ducks possess identical variations, which increase from generation 

 to generation, and if the nature of these changes proves that 

 they must have been due to the effects of use and disuse, then 

 perhaps the transmission of such effects may be admitted ; but 

 it must always be remembered that domestication itself in- 

 fluences the organism, — not only directly, but also indirectly, by 

 the increase of variability as a result of natural selection. Such 

 experiments have not yet been carried out in sufficient detail." 



If Profs. Weismann, Romanes, and Lankester, would agree 

 to some such experiment as the above as definitely proving the 

 point in question (I say "definitely," for the sentence which 

 reads " if the nature of these changes proves that they must have 

 been due to the effects of use and disuse," seems to leave a loop- 

 hole for escape, even if the experiment were carefully carried 

 out), there are two ways in which it might be effected. One is, 

 that the British Association, which by devoting time to the dis- 

 cussion of the hypothesis has shown an appreciation of its worth, 

 should at its next meeting appoint a committee, with a small 

 grant for necessary expenses, to carry out the investigation. The 

 other is, that rit should be undertaken independently by the 

 foremost of those on both sides who are interested in the ques- 

 tion, and who would no doubt subscribe among themselves 

 enough for the purpose in view — at least, speaking for myself, 

 I should not object to contribute to the expenses of a properly 

 planned investigation. 



Regarding the place where the "wild ducks," or possibly 

 some animal with a more frequent recurrence of broods, should 

 be located for observation, I would suggest that the Zoological 

 Society should be asked to afford space in their Gardens at 

 Regent's Park. F. Howard Collins. 



Churchfield, Edgbaston. 



Galls. 



The difficulty raised by Mr. Wetterhan (Nature, February 

 27, p. 394) appears at first sight a serious one, but I think it 

 vanishes on examination. Supposing the attacks of the insects 

 to be constant, trees in their evolution would have to adapt 

 themselves to these circumstances, just as they have adapted 

 themselves to the environment of soil, air, light, wind, and so 

 forth. But the fallacy (as it seems to me) of Mr. Wetterhan's 

 argument lies in the supposition that the life of an oak-tree as 

 such, and the life of an insect, may rightly be compared. A tree 

 is really a sort of socialistic community of plants, which 

 continually die and are supplanted by fresh. Bud-variation is 

 a well-known thing, and in oaks A. de Candolle found many 

 variations on the same tree. Now is it unreasonable to suppose 

 that internal-feeding insects might fake advantage of such 

 variation — or rather, be obliged to take advantage of it, if it 

 were in a direction to benefit the tree ? I will give two 

 purely hypothetical instances, to illustrate the points involved. 

 Imagine two oak-trees, each with three branches, and each 

 attacked by three internal-feeding insects. The insects infesting 

 one tree are borers ; those on the other tree are gall-makers. 

 The borers bore into the branches, which they kill while 

 undergoing their transformations : the tree posibly does not 

 die that year, but next year the progeny of the three, being 

 more numerous while the tree is weaker, effect its destruction, 

 and finally the insects perish for want of food. On the other 

 tree, the gall-makers do no appreciable damage, and the tree is 



