ioo THEORIES OF EVOLUTION 



are several others, upon which I will dwell only for a 

 moment because these two alone command any very 

 large amount of attention at the present time. 



In the first place, Lamarck's theory of the innate 

 tendency towards progressive perfection in animals is 

 not held in exactly that form, but some zoologists in the 

 United States and other countries believe that they see 

 evidence in the rise and fall of certain groups of fossil 

 animals for the existence of a tendency towards extinc- 

 tion, or a tendency towards sudden growth, which lies 

 within the animal itself and is not determined by any 

 external cause. That is a very close approach to 

 Lamarck's original principle of an innate tendency in 

 one direction or another. I will not discuss it at any 

 length, because I think that this evening if we can get 

 a clear idea and attempt some discussion of the merits 

 of the two main theories of evolution, that will be as 

 much as we can expect. I will only say with regard 

 to the subject that arguments based upon fossil remains 

 are apt to be somewhat dangerous, because we have, 

 at least so far as the conditions of life are concerned, 

 so small an amount of evidence. In certain parts of 

 Africa, for instance, the presence of the tse-tse fly 

 absolutely limits the existence of some of the larger 

 quadrupeds. Wherever that fly is, the animal cannot 

 exist. It is very possible that in future times skeletons 

 will be found in specially large numbers on the borders 

 of districts where the fly abounded, and any attempt 

 to argue, from the appearance of the skeletons them- 

 selves, as to the causes of this great extinction will 

 obviously be entirely false and misleading. We have 

 in the skeleton of an animal so small an indication of 

 the events of its life and the conditions of its death, 

 that it is, except in very rare cases, most unsafe to argue 

 as to the causes of its extinction. 



Another theory of evolution is one which has been 

 brought forward by Professor Geddes of Edinburgh. He 

 believes that there is an innate tendency towards growth 

 and towards that dissipation of matter which constitutes 

 its reverse,— the anabolic and katabolic tendencies, as he 



