Morals and the Evolution of Man

A very well-known experiment in animal psychology was once made by Mobius. An aquarium was divided into two compartments by means of a pane of glass; in one of these a pike was put and in the other a tench. Hardly had the former caught sight of his prey, when he rushed to the attack without noticing the transparent partition. He crashed with extreme violence again the obstacle and was hurled back stunned, with a badly battered nose. No sooner had he recovered from the blow than he again made an onslaught upon his neighbour--with the same result. He repeated his efforts a few times more, but succeeded only in badly hurting his head and mouth. At last a dim idea dawned upon his dull mind that some unknown and invisible power was protecting the tench, and that any attempt to devour it would be in vain; consequently from that moment he ceased from all further endeavours to molest his prey.