20 PRESIDENTIAL ADDRESS. 
The Mesozoic mammals were all quite small, and we do not 
know the structure of their feet, so we cannot say whether 
they were arboreal or not; but, with this possible exception, 
we find that the different classes came into existence just 
when they were wanted. 
We must remember that these groups of plants and 
animals form widely separated branches of the tree of life, 
and that the necessary correlations, of which I have been 
speaking, lie outside the jurisdiction of natural selection, 
which, although it regulates the development of each branch, 
has no power of co-ordination between two branches unless 
one forms the food for the other. So that there is no reason 
at all why they should have been developed in the particular 
order in which they appear. 
For example, the origin of birds depends chiefly on the 
development of highly ‘complex papille in the skin, from 
~which the feathers are formed. If these had not been de- 
veloped in the naked skin of a reptile, flying birds would 
never have come into existence. And, if there had been no 
birds, or even if their origin had been delayed until the 
Miocene Period, there would have been no monkeys nor 
man. _ So, also, if no ruminants had been developed, this 
would not have prevented the appearance of apes, or even 
of man; but man would have remained in the stage of a 
hunter all his days, and could not have lived in large com- 
munities. 
Now, if there had been only two of these groups, we might 
reasonably have said that it was by mere chance that the 
one was developed before the other. But when we see 
that there were more than two highly complex combinations, 
all of which happened in the particular order required for 
progress, it is evident that the probabilities are in favour of 
this particular, either by guidance or by pre-arrangement. 
I see no escape from this conclusion. 
SECONDARY CAUSES. 
But granted, what perhaps no one seriously disputes, 
that evolution is due to intelligent design, the difficult ques- 
tion arises: Has all been brought about by unalterable 
secondary laws imposed on matter at the creation of the 
Universe? Or can we recognise any evidence of guidance 
in a particular direction without which the design would 
have failed ? 
When we think of the whole work that has been accom- 
plished by evolution, we are overwhelmed by its vastness. 
The results of organic evolution, particularly, are so mar- 
