394 SECTIONAL TRANSACTIONS.—D. 
SECTION D.—ZOOLOGY. 
Thursday, September 24. 
PRESIDENTIAL ADDRESS by Prof. E. B. Poutton, F.R.S8., on A Hundred 
Years of Evolution (see page 71). 
Prof. J. 8. Huxtey.—Development and Evolution. 
Mr. E. B. Forp.—Mendelism, Genetics, and Evolution. 
Dr. F. A. Drxey, F.R.S.—WNatural Selection and Evolution. 
Natural Selection is the keystone of the Darwinian position. Its recognition by 
Darwin and Wallace rationalised previous evolutionary theory. Natural Selection is 
a logical necessity, arising from the fact of over-production of offspring. But in the 
absence of inheritable variation it could not lead to progressive development. 
Inheritable variation, however, is an ascertained fact. Mendel has shown under 
what limitations it can appear in successive generations of offspring. Subsequent 
work on the lines laid down by Mendel, and especially in the hands of Fisher, Haldane 
and Ford, has established that selection is a necessary feature in the application of 
Mendelian fact to evolutionary theory. It is impossible to over-estimate the import- 
ance of adaptation ; but to suppose that a complicated adaptation, such as that of 
an aquatic derived from a terrestrial mammal, has arisen as a sport or saltation, is 
equivalent to reviving the doctrine of special creation. Adaptation has evidently 
been gradual, and can most reasonably be supposed to have taken place by means 
of natural selection. That some kinds of variation imply a certain amount of correla- 
tion has been thought to be a difficulty ; but it has been shown that one germinal 
element, or perhaps a linkage of two or more elements, can control more than one 
somatic feature. This kind of correlation is obviously different from the elaborately 
specialised adaptation of an aquatic organism such as a whale. On the other hand it 
has been argued that a simple change of small amount can have no selection value. 
Evidence to the contrary can be brought from many quarters, and especially from 
the phenomena of insect mimicry, from which it may be presumed that similar condi- 
tions prevail elsewhere. Natural Selection has been shown by Darwin and his 
successors to be a rational factor in the course of evolutionary development ; it has 
' been recognised as such by the chief workers in the field of genetics ; and objections 
brought against its competence in the formation of species disappear on close 
examination. 
Prof. H. Farrriexp Ossorn.—Nine New Principles of Evolution 
revealed by Paleontology. 
The ratio of vertebrate species known in Darwin’s time—8,767 species—to those 
known in 1925—65,939 species—nearly 8 to 1, is about the measure of the biological 
progress of the first century of evolution. From the completely solved ‘ origin of 
species ’ problem we now concentrate on the ‘ origin of new characters and co-ordina- 
tion of single characters ’ in the lower animals and in man as the outstanding problem 
of the second century of evolution, to which the combined research of zoologists and 
paleontologists should be applied. 
To the palzontologist experimental zoology is pure Darwinism camouflaged ; the 
zoologist sees the temporary and accidental, the paleontologist the secular and 
eternal. As compared with eleven principles of adaptation revealed in zoology from 
Aristotle to the present time, intensive paleontology reveals nine principles of bio- 
mechanical adaptation. 
The eleven zoological principles of individual development, named in the order 
of discovery and prefixed with the terms onto-, auto- or co-, are: retrogression, pro- 
gression, compensation, economy, change of proportion, co-adaptation, acceleration, 
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