218 SOCIAL BEHAVIOUR 
the insects come forth in the midst of a community in full 
social activity would tend to the imitative or intelligent acqui- 
sition of like modes of procedure. It is difficult to distinguish 
the share taken by these two factors which may well co- 
operate. And if natural selection is exercising its influence 
through the elimination of those which do not fall into line 
in social behaviour, there would be ample opportunity for the 
survival of coincident variations.* If one may be allowed to 
speculate, it seems probable that the interaction of instinct 
and intelligence will be found with fuller knowledge to suffice 
for the explanation of the facts, without calling in the known 
but here improbable factor of rationality or any factors un- 
known elsewhere in psychology. 
Some interesting observations of Lord Avebury’s are some- 
times quoted as evidence that ants are lacking in intelligence, 
but (if we accept the distinction already drawn t) they seem 
rather to show the lack of reason. “I placed food,” he says, ¢ 
“in a porcelain cup, on a slip of glass surrounded. by water, 
but accessible to the ants by a bridge, consisting of a strip of 
paper two-thirds of an inch long and one-third wide. Having 
then put an ant (Formica nigra) from one of my nests to this 
food, she began carrying it off, and by degrees a number of 
friends came to help her. When about twenty-five ants were 
so engaged, I moved the little paper bridge slightly, so as to 
leave a chasm just so wide that the ants could not reach 
across. They came to the edge and tried hard to get over, 
but it did not occur to them to push the paper bridge, though 
the distance was only about one-third of an inch, and they 
might easily have done so. After trying for about a quarter 
of an hour they gave up the attempt and returned home. 
This I repeated several times. Then, thinking that paper 
was a substance to which they were not accustomed, I tried 
the same with a bit of straw one inch long and one-eighth of 
an inch wide. The result was the same. Again, I placed 
particles of food close to and directly over the nest, but 
* See p. 37. t Supra, p. 138. 
t ‘‘ Scientific Lectures,” pp. 80-82. 
