Darwin's theory of natural selection issued a profound challenge to orthodox thought and belief: no being or species has been specifically created; all are locked into a pitiless struggle for existence, with extinction looming for those not fitted for the task. Yet The Origin of Species (1859) is also a humane and inspirational vision of ecological interrelatedness, revealing the complex mutual interdependencies between animal and plant life, climate and physical environment, and—by implication—within the human world. Written for the general reader, in a style which combines the rigour of science with the subtlety of literature, The Origin of Species remains one of the founding documents of the modern age.