80 SECTIONAL ADDRESSES. 
An often repeated objection to Natural Selection is the difficulty or 
impossibility of accounting for the earliest stages of useful structures. 
It is, of course, unwise to attempt an explanation of an unknown origin. 
We can only await further discoveries and oftentimes admit that there is 
little hope of success. But the difficulty is frequently completely met by 
Anton Dohrn’s principle of ‘ change of function.’ A new function is often 
taken over by an organ adapted to perform another, the two at first over- 
lapping and the younger gradually supplanting the older. The various 
uses of Vertebrate limbs supply a good illustration. 
Another valuable principle, working in association with Anton Dohrn’s, 
is the “ Organic Selection ’ of Mark Baldwin, Lloyd Morgan and Fairfield 
Osborn. The power of individual adaptability ‘acts as the nurse by 
whose help the species ... can live through times in which the needed 
inherent variations are not forthcoming.’ But this power of adaptability 
is itself a product of selection. ‘ The external forces which awake response 
in an organism generally belong to its inorganic (physical or chemical) 
environment, while the usefulness of the response has relation to its 
organic environment (enemies, prey, &c.). Thus one set of forces supply 
the stimuli which evoke a response to another and very different set of 
forces.’ 14 
What other theories of evolution have been offered to us by those who 
would reject or limit the power of Natural Selection ? Some of them have 
been mentioned by a writer in a recent number of Natwre!’— ortho- 
genic variations,’ ‘ established organic architecture,’ ‘ metabolic routine,’ 
‘laws of growth’ and ‘ conditions of organic stability.’ Others were named 
in Sir Peter Chalmers Mitchell’s Huxley Memorial Lecture in 1927, and 
I agree with his description of them as a ‘ brood of imaginary vital forces, 
gods placed in machines to account for modes of working we do not 
understand ’ ; although, in many instances, some supposed manifestation 
of an internal developmental force receives a ready explanation along the 
lines suggested by H. W. Bates in his classical paper :—1® 
“The operation of selecting agents, gradually and steadily bringing 
about the deceptive resemblance of a species to some other definite object, 
produces the impression of there being some innate principle in species - 
which causes an advance of organisation in a special direction. It seems 
as though the proper variation always arose in the species, and the mimicry 
were a predestined goal.’ Then, after mentioning other suggested 
hypotheses, he concludes that all are ‘ untenable, and the appearances 
which suggest them illusory. Those who earnestly desire a rational 
explanation, must, I think, arrive at the conclusion that these apparently 
miraculous, but always beautiful and wonderful, mimetic resemblances, 
and therefore probably every other kind of adaptation in beings,)? are brought 
about by agencies similar to those we have here discussed.’ 
The writer in Nature who marshalled his array of supposed develop- 
mental forces, contrasted with them ‘ the old nightmare view of evolution 
1 Poulton in Proc. American Assoc. for Adv. Sci., vol. xlvi., 1897, p. 241. 
15 Vol. 127, March 28, 1931, p. 479. 
16 Trans. Linn. Soc. Lond., vol. xxiii. (1862), Pt. III (1862), Mem. XXXII, p. 514. 
“’ Ttalicised for the purpose of this address. 
