characters, conducted by Weismann and others, will be found in the works of Dr Archdall Reid and Prof. J. Arthur Thomson. The effect of Weismann's teaching has been to undermine the foundation of the theory of evolution associated with the names of Buffon, Lamarck, and Herbert Spencer-a theory accepted by Darwin himself, although relegated to a subordinate place & compared with that assigned to natural selection. Although an immense effect has been produced by Weismann upon the trend of biological opinion, a number distinguished evolutionists remain unconvinced and fill hold to the hypotheses of Buffon and Lamarck.*.

De Vries and Evolution by Mutation, or comparatively large and abrupt steps.

Of the modifications of Darwinian thought proposed

at the present day, by far the greatest attention has been attracted by the rediscovery of Mendel's important memoir, and by de Vries' researches on mutation, or the sudden appearance of large variations, in the eveningprimrose (Enothera lamarckiana). The writings of the great Dutch botanist are exceedingly stimulating. He continually suggests important experiments and observations that require to be made on the commonest plants. His work is everywhere informed with a charming and sympathetic spirit. Our admiration is also called forth by the enterprise which led him to attempt so difficult a task as the production of a new double variety of the 'corn marigold' (Chrysanthemum segetum).

De

Vries estimated his chances of success as follows: From this superficial survey of historical facts, the inference stased upon us that the chance of producing a new double Tasty is good enough to justify the attempt. It has frequently succeeded for practical purposes, why should it not Faceed as well for purely scientific investigation?' (p. 492). Whatever may be the bearing of such an investigation upon the theory of evolution, there can be no doubt about high interest and importance, or of the fine scientific

irit which prompted it.

The conception of evolution by mutation is one that 'See Prof. Marcus Hartog's article in 'The Contemporary Review,'

November 1908, p. 635.

readily suggests itself to the human mind. The idea of the sudden transformation of species by the operation of internal forces is to be found in Darwin's 1837 note-book, before the theory of natural selection had arisen in his mind. The same conception of an intermittent transformation of one species into another is encountered in the Vestiges of the Natural History of Creation.' Whewell, in the History of the Inductive Sciences (vol. iii, pp. 639–640, 2nd ed., 1847), speaks in a very interesting manner of the alternative modes of creation, which, as he suggests, might have been compared by Lyell. Whewell himself is quite ready to discuss Lyell's proposition that the successive creation of species may constitute a regular part of the economy of nature.' The various alternatives he proposed are as follows:

6

'Are these new species created by the production, at long intervals, of an offspring different in species from the parents? Or are the species so created produced without parents? Are they gradually evolved from some embryo substance? Or do they suddenly start from the ground, as in the creation of the poet?'

*

It is interesting to observe-although the modern conception of mutation is clearly stated in the first alternative -how entirely the gradual modification of species is omitted from this category. It is also strange that one who could have written with so open a mind should have kept Darwin's 'Origin' for many years out of the library of the great College of which he was Master.

Darwin and Evolution by Mutation.

Mr C. F. Cox has recently brought together† a number of Darwin's references to large variations; and he regards it as 'one of the tragedies of science that in this matter Darwin should have been ready to surrender his main position rather than to receive and to join forces with those who were coming to his aid, but whom he failed to recognise as friends' (p. 451). The author is, we consider, far too much led away by the natural attractions of novelty and energy, and far too ready to give up

Quoted by Huxley in Life and Letters of Charles Darwin,' ii, 192.

+ Charles Darwin and the Mutation Theory,' 'Annals N. Y. Acad. Sci., vol. xviii, No. 11, pt. II, pp. 431-451.

Darwin's deliberate conclusions, founded on a careful and prolonged consideration of all available facts. Mr Cox, although a warm admirer of Darwin, entirely fails to do justice to him in the following statement:

'He had adapted the erroneous belief that this important
principle natural selection] must be greatly weakened if
not entirely sacrificed if any form of saltation was to be
admited in nature. He had, therefore, wavered between his
loyalty to his cherished hypothesis and his fearless devotion
to truth' (p. 443).

This is an utter delusion. Darwin would have welcomed
mutation, just as he would have welcomed Edward
Forbes' views on the extension of continents across the
great oceans, as a means of overcoming difficulties. It
was his fearless devotion to truth' that prevented him
from accepting
a means of escape when his critical judg-
ment could not approve the evidence on which it stood.

Professor A. A. W. Hubrecht has recently published the rash conclusion that Darwin was, in his earlier writings on evolution and natural selection, quite uncertain whether he should attribute the greater weight to individual differences or to large single variations (mutations), and that in coming to a decision he was much influenced by the views of his friend A. R. Wallace. It is important to settle this question now that it has been raised; and we therefore select for quotation four out of many passages which might be chosen from Darwin's letters in which he not only gives his opinion, but also brings forward weighty reasons in support of it. much on the chance of favourable monstrosities (i.e. great (1) 1860. Please tell him [Prof. Parsons] that I reflected tion to this, indeed it would be a great aid, but I did not and sadden variation) arising. I have, of course, no objecallude to the subject, for, after much labour, I could find

too complex, and too beautiful adaptation, in every structure rences. There seems to me in almost every case too much, to believe in its sudden production. I have alluded under the head of beautifully hooked seeds to such possibility. Monsters are apt to be sterile, or not to transmit monstrous "Darwinism versus Wallaceism,' 'Contemporary Review,' November

1908, pp. 629–634.

peculiarities. Look at the fineness of gradation in the shell of successive sub-stages of the same great formation; I coul give many other considerations which made me doubt sucl view. It holds, to a certain extent, with domestic produc tions no doubt, where man preserves some abrupt change in structure.' (To Asa Gray; 'Life and Letters,' ii, 333, 334.)

(2) 1862. Sir Joseph Hooker having written to Darwin on March 17, 1862, to say that

'Huxley is rather disposed to think you have overlooked saltus, but I am not sure that he is right-saltus quoad individuals is not saltus quoad species-as I pointed out in the Begonia case, though perhaps that was rather special pleading in the present state of science':

Darwin replied next day:

'I am not shaken about "saltus." I did not write without going pretty carefully into all the cases of normal structure in animals resembling monstrosities which appear per saltus. (More Letters,' i, 198.)

(3) 1863 [?]. 'Do you not consider such cases as all the orchids next thing to a demonstration against Heer's view of species arising suddenly by monstrosities?—it is impossible to imagine so many co-adaptations being formed all by a chance blow.'t (4) 1877. 'I have never believed in a new form originating from a single variation.' ('More Letters,' i, 367.) Many other expressions of opinion adverse to the mutationist interpretation may be found in Darwin's letters and volumes, but there is no need of further evidence. While no one had studied large variations so carefully, or knew the extent of their occurrence in nature so well, we must reckon with the fact that Darwin's deliberate judgment gave them no place in the onward movement of evolution.

* More Letters,' i, 198. In this passage Sir Joseph not only replies to Huxley's criticism, but also cuts away the foundation of de Vries' conclusions from his interesting experiments with Enothera lamarckiana. De Vries has certainly never shown that the individual mutations which he can multiply into strains in the shelter of the Botanical Garden at Amsterdam have the power to increase into new species able to hold their own in the wild state. Individual mutations have always been admitted: the origin of a new species by mutation has never been proved.

† To Asa Gray, May 31, 1863 [?] (More Letters,' i, 242.) The following sentence also occurs in a letter to H. Falconer, December 26, 1863: Heer's view that new species are suddenly formed like monsters, I feel a conviction from many reasons is false.' ('More Letters,' i, 244.)

DARWIN AND HIS MODERN CRITICS

Weismann and Evolution by Mutation.

13

It is interesting to observe that the main lines of Weismann's recent criticism of de Vries' hypothesis run parallel with those which prevented Darwin from accepting the views of earlier mutationists. Although writing with warmth and enthusiasm of the interest and novely of de Vries' investigations on the evening-primrose, Weismann considers that the Dutch botanist brously overestimates the value of his facts, interestand important as these undoubtedly are, and under the influence of what is new he overlooks what lies before him-the other aspect of the transmutation of species, to which the attention of most observers since Darwin and Wallace has been almost exclusively devoted I mean the origin of adaptations' (ii, pp. 319, 320). Weismann truly points out that the dominant import

ance of adaptation

is precisely the point at which many botanists cease to understand the zoologists, because among plants there are fewer adaptations than among animals; or, in any case, adaptations in plants are not so readily demonstrated as among animals, which not infrequently seem to us to be entirely built up of adaptations' (p. 320).

It is impossible on the present occasion to give any adequate account of the convincing arguments by which Weismann supports Darwin's conclusions that adaptations, built up as they are of many co-operating and intimately related factors, cannot have arisen as sudden mutations. It is,' as Weismann says, 'in regard to the necessity which exists almost everywhere for the coadaptation of numerous variations of the most different parts, that the "mutation theory" breaks down utterly... Harmonious adaptation requires a gradual, simultaneous, or successive purposive variation of all the parts concerned,' which, Weismann maintains (op. cit. p. 321), can only be secured by means of fluctuating variations.

How far is the Series of Species of Animals and Plants

Continuous or Discontinuous?

The problem of mutation in evolution is evidently chsely connected with the question of continuity or disThe Evolution Theory' (English translation), ii, 317-329..