What is to be said of the behaviour of beavers who gnaw the base of a
tree with their chisel-edged teeth till only a narrow core is left--to
snap in the first gale, bringing the useful branches down to the ground?
What is to be said of the harvest-mouse constructing its nest, or of the
squirrel making cache after cache of nuts? These and many similar pieces
of behaviour are fundamentally instinctive, due to inborn
predispositions of nerve-cells and muscle-cells. But in mammals they
seem to be often attended by a certain amount of intelligent attention,
saving the creature from the tyranny of routine so marked in the ways of
ants and bees.