548 



NATURE 



[Ai'KiL 6, 1899 



studies, and the facts of biology forming the grounds of the 

 evolutionary idea, will be taught in our primary and secondary 

 schools. 



The rapidity with which evolutionary conceptions have taken 

 root and spread may be compared to the rankness of growth of a 

 jirepotent plant or animal on being introduced into a new terri- 

 lor)- where it is free from competition. It has indeed swept 

 everything before it, occupying a field of thought which hitherto 

 had been unworked by human intelligence. 



The immediate effect and a very happy one, of the acceptance 

 of the theory of descent on working zoologists, is to broaden 

 their minds. Collectors of insects and shells, or of birds and 

 mammals, instead of being content simply to acquire specimens 

 for their cabinets, are led to look during their field excursions for 

 examples of protective mimicry, or to notice facts bearing on the 

 immediate cause of variation. Instead of a single pair of speci- 

 mens, it is now realised that hundreds and even thousands col- 

 lected from stations and habitats wide apart are none too many 

 for the study of variation as now pursued. 



The race of " species grinders" is diminishing, and the study 

 of geographical distribution, based as it is on past geographical 

 changes and extinctions, is now discussed in a far more philo- 

 sophical way than in the past. The most special results of work 

 in cytology and morphology are now affording material for 

 broad work in phylogeny and heredity. 



On the other hand it must be confessed that, as the result of 

 the acceptance of evolutionary views, our literature is at times 

 flooded with more or less unsound hypotheses, some tedious 

 verbiage and long-winded, aerial discussions, based rather on 

 assumptions than on facts. But on the whole, perhaps, this is 

 a healthy sign. Too free, exuberant growths will be in the long 

 run lopped off by criticism. 



One tendency should be avoided by younger students, that of 

 loo early specialisation, and of empirical work without a broad 

 survey of the whole field. In some cases our histologists and 

 morphologists rise little above the intellectual level of species 

 describers. Expert in the use of the microtome and of reagents, 

 they appear to have but little more general scientific or literary 

 culture than high-class mechanics The chief antidote, however, 

 to the danger of narrowness is the lessons derived from evolu- 

 tionary thought and principles. 



Finally, as a proof of the value of evolutionary ideas to the 

 present generation, let us suppose for a moment, if it were con- 

 ceivable, that they should be blotted out. The result, it is safe 

 to say, would be equivalent to the loss of a sense. 



It is a matter of history that when a new idea or principle 

 or a new movement in philosophy or religion arises, it at first 

 develops along the line of least resistance ; the leaders of the 

 new thought acquire many followers or disciples. Soon the 

 latter outstrip their teachers, and go to greater extremes ; 

 modifications of the original simple condition or theory occur, 

 and as the final result there arise schisms and differentiations 

 into new sects. This has happened in science, and already we 

 have evolutionists divided into Lamarckians and Darwinians, 

 with a further subdivision of them into Neolamaickians and 

 Neodarwinians, while the latter are often denominated Weis- 

 mannians. Some prefer to rely on the action of the primary 

 factors of evolution, others believe that Natural Selection 

 embraces all the necessary factors, while still others are 

 thoroughly persuaded of its inadequacy. 



The result of this analytical or differentiating process will 

 probably be an ultimate synthesis, a belief that there is a com- 

 plex of factors at work. Of these factors those originally 

 indicated by Lamarck, with the supplementary ones of com- 

 )ietition and natural selection bequeathed by Darwin, are the 

 most essential and indispensable, and it is difficult to see how 

 they can be displaced by other views. Meanwhile all agree, and 

 it was never more firmly established than at this moment, that 

 there is and always has been unceasing energy, movement, and 

 variation, a wonderful adaptation and harmony in nature, 

 between living beings and their surroundings. 



The present status of evolution in its different phases or 

 attitudes since the time of the appearance of Darwin's "Origin 

 of Species" may be roughly pointed out as follows : — 



(1) The claim by some thinkers of the inadequacy of 

 Darwinism, as such, or Natural Selection, to account for the 

 rise of new species, and the a.ssignnient of this factor to what 

 they believe to be its proper place among the other factors of 

 organic evolution. 

 ^ (2) The renaiscence of Lamarckism'under the name of Neola- 



NO. 1536, VOL. 59] 



marckism, being Lamarckism in its modern form. This school 

 relies on the primary factors of evolution, on changes in the 

 environment, such as the agency of the air, light, heat, cold, 

 changes in climate, use and disuse, isolation, and parasitism, 

 while it regards natural, sexual, physiological, germinal and 

 organic selection, competition or its absence, and the inheritance 

 of characters acquired during the lifetime of the individual, as 

 secondary f.iclors, calling into question the adequacy of natural 

 selection as an initial factor. 



(3) The rise of the Neodarwinian school. While Darwin, 

 .soon after the publication of the "Origin of Species " somewhat 

 changed his views as to the adequacy of natural .selection, and 

 favoured changes in the surroundings, food, &c. , as causes of 

 variation, his successors, Wallace, Weismann, and others believe 

 in the " allsulticiency " of natural selection. Weismann also 

 invokes panmixia, or the absence of natural .selection, as an 

 important factor ; also amixia, and denies the principle of in- 

 heritance of acquired characters, or use-inheritance. 



(4) A third school or sect has arisen under the leadership of 

 Weismann, who advocates what is in its essence apparently a 

 revival of the exploded preformation, encasement, or " evolu- 

 tion " theory of Swammeidam, Bonnet and llaller, as opposed 

 to the epigenetic evolutionism of Harvey, Wolff, Baer, and the 

 majority of modern embryologists. On the other hand, there 

 are some enibryologisis who appear to accept the combined 

 action of epigenesis and evolution in development. 



(5) Attention has been concentrated on the study of 

 variations and of their cause. Opinion is divided as to whether 

 variation is fortuitous or definite and determined. Many now 

 take exception to the view, originally held by Darwin, that 

 variations are purposeless and fortuitous, believing that they are, 

 for example, dependent on changes in the environment which 

 were determined in early geological periods. For definite 

 variation Eimer proposes the term orthogenesis. Minute 

 variations dependent on climatic and other obscure and not 

 readily appreciable causes are now brought out clearly by a 

 system of varied and careful quantitative measurements. 



(6) More attention than formerly is given to the study ot 

 dynamical evolution, or kinetogenesis : to the effect of external 

 stimuli, such as intermittent pressure, mechanical stresses and 

 tensions by the muscles, &c., on hard parts. Originally sug- 

 gested by llerberi Spencer, that the ultimate cause or mechanical 

 genesis of the segmentation of the vertebrate skeleton was due 

 to transverse strains, the segmentation of the bodies of worms 

 and arthropods, as well as of vertebrates, has been discussed by 

 recent workers (Rider, Cope, Meyer. Tornier, Hirsch, and 

 others). Here should be mentioned the work done in general 

 physiology, or morphogenesis, by Verworn, Davenport, and 

 others. ALso the discoveries of I'asteur, and the application by 

 Metschnikoff and of Kowalevsky of phagocytosis to the de- 

 struction and renewal of tissues during metamorphosis, bear 

 closely on evolutional problems. 



(7) A new field of research founded by Semper, Vilmorin, and 

 Plateau, and carried on by De Varigny, is that of experimental 

 evolution, involving the effects of artificial changes of the 

 medium, including temperature, food, variation in the volume 

 of water and of air. absence of exercise, movement, i\;c. .Vlso 

 should be added horticultural experiments which have been 

 practised for many years, as well as the results of acclimatisation. 



Here should be mentioned the experiments bearing on the 

 mechanics of development (Entwickelungsmechanik der organ- 

 ismen), or experimental embryolog)', of Oscar 1 lertwig, Roux, 

 Drie.sch, Morgan and others, and the curious results of animal 

 grafting and of mutilations of the embryos, obtained by Born 

 and others, as well as the regeneration ot parts. The remark- 

 able facts of adaptation to new and unfavourable conditions of 

 certain embryos are as yet unexplained, and have led to con- 

 siderable discussion arid research. 



(8) The .) priori speculations of Darwin, Gallon, Spencer, 

 Jaeger, Nusbaum. Weismann and others, based on the results 

 of the labours c^f morphologists and cytologists, have laid the 

 foundation fur a lluory of the physical basis of heredity, and 

 for the suppo-.iiioii that the chromatin in the nucleus of repro- 

 ductive cells is the bearer of heredity. The theory has already 

 led to prolonged discussions, and opened up new lines of work 

 in cytology and embryology. 



(9) The subject of instinct, discussed from an evolutional point 

 of view, Ijoth by morphologists and psychologists, particularly 

 by Lloyd Mi'rg:iii, has come to the front, while mental evolution 

 has been discussed b\ Romanes and others. 



