The book presents a comprehensive defense of pure Darwinism, examining the origin of species through natural selection rather than special creation. Wallace establishes the foundation of the theory by analyzing the constant struggle for existence driven by the rapid, geometrical multiplication of all organisms. He details how variability exists in every part of animal and plant anatomy, and how these variations provide the raw material for adaptation to changing environments. The work investigates the divergence of character, showing how allied species adapt to distinct modes of life and occupy vacant places in nature.
Wallace provides extensive evidence of variation in wild species, domestic animals, and cultivated plants, supported by numerous detailed diagrams of physical measurements. The text addresses complex biological phenomena such as the role of protective coloration, mimicry, sexual selection, and geographical distribution of organisms. Furthermore, the volume explores geological evidence of evolution, fundamental problems of heredity, and the application of Darwinism to the origin of man. Throughout the work, Wallace demonstrates the overwhelming importance of natural selection over all other agencies in producing new species.
