peoples, who accredit the “categorical imperative” to some supernatural power, as we are to see in a later section.  The one point that comes out clearly is that the systems of conduct and duties have evolved so as to be very different among various races, and that in the history of any one people, ethics has passed through many varied conditions.  What may be deemed right at one period becomes wrong at another when conditions may be changed; in medieval England the penalty of death was prescribed for one who killed a king’s deer, as well as for a highway murderer.  The Fijian of a quarter century ago killed his parents when they became too old to be effective members of their tribe.  And so deeply ingrained was this principle of duty that elderly people would voluntarily go to a living grave surrounded by their friends; while in other authentic cases, parents have first killed their sons who failed to obey the tribal law, and have then committed suicide.  We can see how nature and necessity would institute a law requiring such conduct where a tribe must carry on almost incessant warfare and where the available food supplies would be enough for only the most efficient individuals.  Infanticide also has been practised for reasons of biological utility, as among the Romans, who at first maintained their racial vigor by deliberately ordering the death of weak babes.  But times have changed, and ethics has become very different with passing decades.  Our civilization has resulted in a development of human sympathy as an emotional outgrowth of necessary altruism; this motive directs us through charitable institutions and hospitals to prolong countless lives which are more or less inefficient, but which do not render the whole body politic incompetent in its struggle for existence.

Nature then has itself attended to the development and institution of ethics.  As we look back over the long series of stages leading to our own system of conduct the most striking feature of the history is the increasing power of self-control or inhibition.  As a natural instinct this tends to prevent the committing of acts which for one reason or another are naturally harmful to society as a whole.  What we call conscience is an instinct implanted by purely natural factors, and it unconsciously turns the course of human action in the directions of selfish and altruistic interests.  Conscience, then, without ceasing to have validity and efficiency, appears on the same plane with all of the other products of evolution which owe their existence to individual or social utility.