210 Robertson: Theories of Evolution. 
embittered struggle for priority which has sometimes occurred 
when the same discovery has been made independently and almost 
simultaneously by two workers, Darwin and Wallace each 
showed the greatest anxiety to give each other all possible 
credit. Wallace arrived at the idea of Natural Selection much 
more rapidly than Darwin. He tells us that after three years 
pondering on the subject it came to him in a sudden inspiration 
while he was suffering from a severe attack of ague in the 
Moluccas ; he sketched out the whole theory in a day and sent 
it straight to Darwin. 
The ‘ Origin of Species’ is a long book, which from cover to 
cover consists of one closely-wrought argument of which no 
shortened and condensed account can be anything but un- 
satisfactory ; however, I will try in the briefest possible way 
to summarise the main contentions. In the ‘Origin of Species’ 
Darwin attempted to answer two distinct questions :— 
1. Were the animals and plants of the present day created 
just as we now know them, or have they been gradually evolved ? 
In answer to this question Darwin brings forward much 
evidence to show that the Evolution hypothesis is the only 
tenable one. 
2. If it be granted that Evolution has occurred, how has it 
been brought about ? 
Darwin’s answer to this was that it had been mainly brought 
about by the action of Natural Selection on small spontaneous 
variations, occurring in all directions, good, bad, and indifferent. 
In discussing the ‘ Origin of Species’ considerable confusion 
often arises because these two questions are not kept distinct. 
People talk as if Darwinism or Natural Selection were the same 
thing as Evolution, and as if the idea of Evolution would stand 
and fall with the idea of Natural Selection. But in reality, if 
Darwin’s hypothesis of Natural Selection were disproved, this 
would leave the Evolution theory quite untouched, since the 
hypothesis of Natural Selection is simply put forward to explain 
how Evolution occurs. A concrete illustration may perhaps. 
make this clearer. Suppose a passenger on a ship takes 
observations of the stars at intervals, and to explain 
his observations puts forward the theory that the vessel is. 
moving, and that the movement is taking place: in a certain 
direction. Then suppose that other evidence, such as the 
presence of sails, leads the passenger to form a second theory— 
namely, that the agency by which the ship is moved is wind. 
Now imagine that he presently discovers that the ship is really 
Naturalist, 
