September 3, 1914I 



NATURE 



n 



followed the unloading of Gondwanaland and the 

 heavy loading of the adjoining ocean bed along a band 

 roughly parallel to the present Himalayan folds. 



R. S. Woodward objected that isostasy does not 

 seem to meet the requirements of geological con- 

 tinuity, for it tends rapidly towards stable equilibrium, 

 and the crust ought therefore to reach a stage of 

 repose early in geologic time.'" If the process of 

 denudation and rise, with adjoining deposition and 

 subsidence, occurred on a solid globe, this objection 

 might hold good. But it seems to me that the break- 

 up of Gondwanaland and the tectonic revolutions that 

 followed show how isostasy can defeat itself in the 

 presence of a subcrustal magma actually molten or 

 ready to liquefy on local relief of pressure. It is pos- 

 sible that the protracted filing off of Gondwanaland 

 brought nearer the surface what was once the local 

 level of no-strain and its accompanying shell of 

 tension. 



The conditions existing in northern Gondwanaland 

 before late Mesozoic times must have been similar to 

 those in south-west Scotland before the occurrence of 

 the Tertiary eruptions, for the crust in this region was 

 also torn by stresses in the S.W.-N.E. direction with 

 the formation of a remarkable series of N.W.— S.E. 

 dykes which give the i-in. geological maps in this 

 region a regularly striped appearance. 



There is no section of the earth's surface which one 

 can point to as being now subjected to exactly the 

 same kind and magnitude of treatment as that to 

 which Gondwanaland was exposed for long ages before 

 the outburst of the Deccan Trap ; but possibly the 

 erosion of the Brazilian highlands and the deposition 

 of the silt carried down by the Amazon, with its 

 southern tributaries, and by the more eastern Araguay 

 and Tocantins, may result in similar stresses which, 

 if continued, w-ill develop strains, and open the way 

 for the subjacent magma to approach the surface or 

 even to become extravasated, adding another to the 

 small family of so-called fissure-eruptions. 



The value of a generalisation can be tested best by 

 its trustworthiness as a basis for prediction. Nothing 

 shows up the shortcomings of our knowledge about 

 the state of affairs below the superficial crust so effec- 

 tually as our inability to make any useful predictions 

 about earthquakes or volcanic eruptions. For many 

 years to come in this department of science the only 

 worker who will ever establish a claim to be called a 

 prophet will be one in Cicero's sense — " he who guesses 

 well.- 



SECTION D. 



ZOOLOGY. 



Opening Address by Prof. Arthur Dendy, D.Sc, 

 F.R.S., President of the Section. 



Progressive Evolution and the Origin of Species. 



The opening years of the present centun,- have 

 witnessed a remarkable development of biology as an 

 experimental science, a development which, however 

 full of promise it may be for the future, for the time 

 being appears to have resulted in a widespread dis- 

 turbance of ideas which have themselves only recently 

 succeeded in gaining general acceptance. The theory- 

 of organic evolution, plainly enough enunciated at the 

 close of the eighteenth and the beginning of the nine- 

 teenth century by Buffon, Lamarck, and Erasmus 

 Darwin, remained unconvincing to the great majority 

 of thinking men until the genius of Charles Darwin 

 not only brought together and presented the evidence 

 in such a manner that it could no longer be ignored, 



^ " Address to the Sect, o' Mathematics and Astronomy of the Amer. 

 As-soc.," 1889. Smithsonian Report, 1S90. p. 196. 



NO. 2340, VOL. 94] 



but elaborated a logical explanation of the way in 

 which organic evolution might be supposed to have 

 taken place. Thanks to his labours and those of 

 Alfred Russel Wallace, supported by the powerful 

 influence of such men as Huxley and Hooker, the 

 theory was placed upon a firm foundation, in a posi- 

 tion which can never again be assailed with an\ 

 prospect of success. 



This statement is, I believe, entirely justified with 

 regard to the theorv- of organic evolution itself, but 

 the case is very different when we come to investigate 

 the position of the various subsidiar}- theories which 

 have been put forward from time to 'time with regard 

 to what may perhaps be termed the modus operandi, 

 the means by which organic evolution has been 

 effected. It is in this field that controversy rages more 

 keenly than ever before. Lamarck told us that 

 evolution was due to the accumulated results of indi- 

 vidual effort in response to a changing environment, 

 and also to the direct action of the environment 

 upon the organism. Darwin and Wallace taught us 

 that species originated by the natural selection of 

 favourable variations, and under the influence of 

 Weismann's doctrine of the non-inheritance of 

 acquired characters the theory of natural selection is 

 in danger of becoming cr}stallised into an inflexible 

 dogma. In recent years De Vries has told us that 

 species arise by sudden mutations, and not by slow 

 successive changes, while one of the most extreme 

 exponents of " Mendelism," Prof. Lotsy, lately in- 

 formed us that all species arise by crossing, and. 

 seriously suggested that the vertebrate tjrpe arose by 

 the crossing of two invertebrates ! 



This curious and many-sided divergence of opinion 

 amongst expert biologists is undoubtedly largely due 

 to the introduction of experimental methods into bio- 

 I logical science. Such methods have proved ver\- fruit- 

 ful in results which at first sight seem to be mutually 

 contradictor^', and each group of workers has built up 

 its own theory mainly on the basis of observations in 

 its own restricted field. 



Prof. Bateson has said in his recently published 

 " Problems of Genetics " : "When . . . we contemplate 

 the problem of evolution at large the hope at the 

 present time of constructing even a mental picture of 

 that process grows weak almost to the point of 

 vanishing. We are left wondering that so lately men 

 in general, whether scientific or lay, were so easily 

 satisfied. Our satisfaction, as we now see, was chieflj' 

 founded on ignorance." ^ 



In view of this striking pronouncement on the part 

 of one who has devoted his life with signal success 

 to the experimental investigation of evolutionary 

 problems, the remarks which I propose to lay before 

 you for your consideration to-day may well appear 

 rash and ill-advised. I cannot believe, however, that 

 the position is really quite so black as it is painted. 

 We must perforce admit that the divers theories with 

 regard to the working of organic evolution cannot all 

 be correct in all their details, but it may be that each 

 contains its own elements "of truth, and that if these 

 elements can but be recognised and sorted out, they 

 may perhaps be recombined in such a form as to afford 

 at any rate a plausible working hypothesis. We must 

 bear in mind from the outset that in dealing with such 

 a complex problem many factors have to be taken into 

 account, and that widely different views on the ques- 

 tion may be merely one-sided and not necessarily 

 mutually exclusive. 



I take it there are three principal facts, or groups 

 of facts, that have to be accounted for by any theory 

 of organic evolution : — 



(1) The fact that, on the whole, evolution has taken 



j 1 " Problems of Genetic*," p. 97. 



