It is always to be borne in mind in considering this class of crimes
that the motive power of life is not reason but instinct. If men lived
by reason the race would not survive. The primal things that preserve
the race, the hunger for food, drink, sex, are instinctive and not only
are not awakened or satisfied by reason, but oftentimes in violation of
it. Nature, first of all, sees to the preservation of the species, and
acts in a broad way that life may not perish. Nature knows nothing about
right and wrong in the sense in which man uses these words. All of our
moral conceptions are purely of social origin and hence not instinctive
in human life, and are forever giving way to the instincts on which
Nature depends. The preservation of life has called for the emotions of
hate, fear and love, among the other emotions that move men. The animal
fears danger and runs away, and thus life is preserved. The weaker
animal is almost entirely dependent for life upon his fear. He is
sometimes afraid when there is no danger, but without fear he would be
destroyed. Sometimes the animal hates and kills and thus preserves
himself. The love of offspring is the cause of the care bestowed upon it
which preserves its life. The herd instinct in animal species develops
packs and clans and tribes and states. Man is the heir to all the past,
and the instincts and emotions of the primitive animal are strong in his
being. These may have been strengthened or diluted as the ages have come
and gone, but the same instincts furnish the motive power for all his
acts. Man fears and hates, and runs or kills and saves his life. He
loves, and preserves his offspring.

Man sees an object. Instinctively he may fear it or he may hate it. He
may run from it or destroy it. He gathers impressions through his
senses. The nerves carry them to the brain. He comes to fear certain
persons and things, to hate certain other persons or things, and to
love still others. If the hatred is strong enough or the danger great