In the struggle for survival, the fittest win out at the expense of their rivals because they succeed in adapting themselves best to their environment.
The love of a dog for his master is notorious; in the agony of death he has been known to caress his master, and everyone has heard of the dog suffering under vivisection, who licked the hand of the operator; this man, unless he had a heart of stone, must have felt remorse to the last hour of his life.
