trajVsactions of section d. 887 



Section D.— ZOOLOGY (INCLUDING ANIMAL PHYSIOLOGY). 



President of, the Section. — W. F. R. Weldon, M.A., F.R.S., Professor 

 of ComparatiTe Anatomy and Zoology, University College, London. 



THURSDAY, SEPTEMBER 8. 



The President-delivered the following Address: — 



In attempting to choose the subject of the address with which custom obliges your 

 President to trouble you, I felt that I should have the best hope of interesting you 

 if I decided to speak to you on the subject most interesting to myself. I therefore 

 propose to discuss, as well as I can, the principal objections which are urged against 

 the theory of Natural Selection, and to describe the way in which I think these 

 objections may be met. 



The theory of Natural Selection is a theory of the importance of differences 

 between individual animals. In the form in which Darwin stated it, the theory 

 asserts that the smallest observable variation may affect an animal's chance of 

 survival, and it further asserts that the magnitude of such variations, and the 

 frequency with which they occur, is governed by the law of chance. 



Three principal objections are constantly brought forward against this theory. 

 The first is that the species of animals which we know fall into orderly series, and 

 that purely fortuitous variations cannot be supposed to afford opportunity for the 

 selection of such orderly series ; so that many persons feel that if the existing 

 animals are the result of selection among the variable offspring of ancestral 

 creatures, the variations on which the process of Natural Selection had to act must 

 have been produced by something which was not chance. 



The second objection is that minute structural variations cannot in fact be sup- 

 posed to affect the death-rate so much as the theory requires that they should. 

 And it is especially urged that many of the characters by which species are dis- 

 tinguished appear to us so small and useless that they cannot be supposed to affect 

 the chance of survival at all. 



The third objection is that the process of evolution by Natui-al Selection is so 

 slow that the time required for its operation is longer than the extreme limit of 

 time given by estimates of the age of the earth. 



Now the first of these three objections, the objection to fortuitous variation as 

 the source of the material on which Natural Selection can act, is veiy largely due 

 to a misunderstanding of the meaning of words. The meaning of the word Chance 

 is so thoroughly misunderstood by a number of writers on evolution that I make 

 no apology for asking you to consider what it does mean. 



Consider a case of an event which happens by chance. Suppose I toss a penny, 

 and let it fall on the table. You will agree that the face of the penny which looks 

 upwards is determined by chance, and that with a symmetrical penny it is an even 

 chance whether the * head ' face or the ' tail ' face lies uppermost. For the moment, 

 that is all one can say about the result. Now compare this with the statements we 

 can make about other moving bodies. You will find it stated, in any almanae, 

 that there will be a total eclipse of the moon on December 27, and that the eclipse 



