Darwin's monumental work is divided into fifteen chapters, reflecting the blocks upon which the theory of evolution was built. Population growth, extinction, physiology, habit, instinct, geology, geography and morphology are discussed. The geological record was of great importance to Darwin. Fossils provided evidence. The naturalist seems to have examined or at least contemplated the entire development and existence of all flora and fauna known at the time.In his introduction, Darwin expresses the notion that the embryological similarities of organisms led to a belief that species are linked through ancestry. The naturalist argues that such a conclusion is wrong without including the concepts of modification and coadaptation. The first chapter deals with the concept of domestication, differences resulting from the purposeful raising of species versus a natural existence. Darwin felt that the influence of generations was necessary for large variation. Furthermore, he stated that the changes would continue for some time. Wheat and long-utilized domestic animals are used as examples.Two factors are pointed to as primary in effecting change: the nature of the being and the environment, in other words, internal and external factors. According to Darwin, selection, conscious and unconscious, proved the dominant force, with unpredicted influences most influential. The author mentions several scientists, their specialties and their contributions to his theory.
Scenarios such as the dominance of a variant over the parent species stand as bases from which Darwin extrapolated. Adaptation, resulting from opportunity led to Darwin developing his theory of survival of the fittest. A duck's webbed feet, a vulture's bald head and a giraffe's long neck are some of the specific adaptations discussed. Origin of Species provides a detailed examination of habit and species, from horses to pigeons. Chapter six provides questions logically arrived at from a study of evolutionary theory. Darwin addresses these questions in his consistently thorough manner.Chapter eight provides a difference between instinct and habit. Darwin and others felt that instinct could be altered, as opposed to the constancy of habit.The book concludes with the naturalist's contemplation of the complexity of life, its interconnectedness and dependence. He reiterates the notion that a simple start has led to wonderful organisms that continue to evolve.Darwin's approach, writing in the first person, lessens the cold analytical tone expected in such a work.