A grain in the balance will determine which individual shall live and which shall die.... Darwins 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 the 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 the Species remains one of the founding documents of the modern age.