The conditions under which much of the behaviour is carried out seem to indicate strong instinctive tendencies which give an hereditary trend to the direction which the social behaviour takes. Dr. Bethe,[100] indeed, goes so far as to regard the behaviour as almost entirely instinctive, affording little evidence of that modifiability of reactions which indicates intelligent guidance. He shows as the result of careful experiment that the behaviour of ants to friends and enemies are direct reactions to smell. Enemies washed with the excretions of members of the nest are treated as friends, notwithstanding their different colour, size, and general appearance. By scent, too, they follow the lead of others and retrace their way to the nest; this, he says, is not the result of a mental process, but is the reaction of a complicated reflex mechanism. As the outcome of careful observation, Dr. Bethe’s conclusions are of great value and interest. But he seems to go too far in denying to ants any power of intelligent accommodation to circumstances. If we admit intelligence, then the fact that the insects come forth in the midst of a community in full social activity would tend to the imitative or intelligent acquisition 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.[101] 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 unknown elsewhere in psychology.