Even amongst the lower animals, misery and distress in one of the flock militate against the happiness of the others.

In a highly developed man true happiness is impossible in the presence of pain and misery in others and _vice versa_; happiness is contagious and flows to us from the joy of others.
If the happiness of others then is so essential to my own happiness, I am fulfilling the first law of life and ministering to my own preservation in health and happiness by using my best endeavours to promote this state in others.

My material comfort too depends largely on the labour, and love, and the contribution of others in the complex industrial system and division of labour of the higher civilisations.
Not only my happiness and health but my very existence depends on the good-will and toil of others.

Thus from a purely egoistic standpoint, my first duty to myself is to increase the happiness in others, and, therefore, my first duty to myself becomes my highest duty to society.
My duty to my child is comprehended in my duty to society, _i.e._, to others.

My duty to others is to increase the sum of the happiness of others, and bringing healthy children into the world not only creates beings capable of experiencing and enjoying pleasures, but adds to the sum of social happiness, by increasing the number of social units capable of rendering service to others.
The next great law of life is the law of race preservation.