Henry Drummond (1851-1897) was a Scottish evangelist, writer and lecturer. Natural Law in the Spiritual World argues that the scientific principle of continuity extends from the physical world to the spiritual, providing common ground for discussions between scientists and religious leaders. His later work, The Ascent of Man, argued that altruism, or the disinterested care and compassion of animals for each other, was an important part in effecting the survival of the fittest.