THE PRESIDENTIAL ADDRESS 19 
and for tracing supplies of water and oil and other resources at 
depth. 
Evolution of life on the earth has been by no means uniform ; 
there have been periods of waxing and waning which may be 
attributed to geographical, climatological, and biological influences. 
The development of large land areas, ranged longitudinally or 
latitudinally, the invasion of epicontinental seas, the isolation of 
mediterraneans or inland seas, the splitting of continental areas 
into archipelagos or the reunion of islands into continuous land, the 
making of barriers by the rearing of mountain chains or the formation 
of straits or arms of the sea, the oncoming of desert or glacial 
climates ; all such factors and many others have been of importance 
in quickening or checking competition, and in accelerating or 
retarding the evolution of life. 
Probably, however, even greater effects have followed the inter- 
action of groups of biological changes on one another. As an 
instance I might recall Starkie Gardner’s estimate of the results 
following upon the first appearance of grasses in the world. This 
seems to have been not earlier than Eocene, and probably late 
Eocene times. By the Oligocene they had made good their hold, 
peculiarities in their growth and structure enabling them to compete 
with the other vegetation that then existed; and gradually they 
spread over huge areas of the earth’s surface, formerly occupied by 
marsh, scrub, and forest. They have, as Ruskin says, ‘a very little 
strength . . . and a few delicate long lines meeting at a point . . . 
made, as it seems, only to be trodden on to-day, and to-morrow to be 
cast into the oven’; but, through their easy growth, their disregard 
of trampling and grazing, and by reason of the nourishment con- 
centrated in their seeds, they provided an ideal and plentiful source 
of food. On their establishment we find that groups of animals, 
which had previously browsed on shrubs and trees, adopted them, 
with consequent alterations and adaptations in their teeth and 
other bodily structures. To follow their food from over-grazed or 
sun-scorched regions they required to be able to migrate easily and 
quickly, and it was essential for them to discard sedentary defence 
and to flee from threatened danger. Such defence as was possible 
with heels, teeth, or horns, they retained; but the dominant 
modifications in their organisation were in the direction of speed 
as their most vital need. 
Side by side with this development, and in answer to increasing 
numbers, came bigger, stronger, and speedier carnivores, to feed on 
prey now so much more abundant, but more difficult to catch. 
