Poulton.l 376 rMayi6, 
In the tirst place, L:iinarck's tlieory of tlie innate tendencj' 
towards progressive perfection in animals is not held in exactly 
that form, but some zoologists in this 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 extinction, 
or a tendency towards sudden growth, which lies within the ani- 
mal 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 get 
some idea and have some discussion on 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 themselves, 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 Scotland. He believes that there 
is an innate tendency towards growth and towards that dissipa- 
tion of matter which constitutes its reverse, — the anabolic and 
katabolic tendencies, as he calls them. But that view, although 
he argues it with much eloquence, has not been widely accepted, 
and I think it will be generally admitted that it does not yet rest 
on sufficient proof. 
In addition to these, there are some who maintain the position 
that there is an unknown cauj^e of evolution. They believe that 
these theories, although one or more of them may be of value, 
are yet insufficient to account for organic evolution. Those who 
take this line are of course logically bound to bring forward the 
