TRANSACTIONS OF SECTION D.—PRESIDENTIAL ADDRESS. 383 
Secrion D.—ZOOLOGY. 
PRESIDENT OF THE SECTION: PRoressor Anruur Denpy, D.Sc., F.R.S. 
MELBOURNE. 
FRIDAY, AUGUST 14. 
The President delivered the following Address :— 
Progressive Hvolution and the Origin of Species. 
Tue opening years of the present century have witnessed a remarkable develop- 
ment 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 disturbance 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 nineteenth 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, 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 position which can never again be assailed with 
any prospect of success. 
This statement is, I believe, entirely justified with regard to the theory 
of organic evolution itself, but the case is very different when we come to 
investigate the position of the various subsidiary 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 individual effort in 
response to a changing environment, and also to the direct action of the environ- 
ment 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 crystallised 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,’ Professor Lotsy, lately informed us that all 
species arise by crossing, and seriously suggested that the vertebrate type 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 
biological science. Such methods have proved very fruitful in results which 
at first sight seem to be mutually contradictory, and each group of workers has 
built up its own theory mainly on the basis of observations in its own restricted 
field. . 
