Charles Lyell's Principles of Geology (1830-33) profoundly influenced Darwin as he voyaged on the Beagle and developed the theory of natural selection. A hugely ambitious attempt to forge links between observable causes - volcanoes, earthquakes, rivers, tides and storms - and the current state of the earth, the Principles proved crucial in the long-running dispute between science and Scripture. Its clarity, broad sweep, sheer intellectual passion and panache caught the imagination of Melville, Emerson, Tennyson and George Eliot as well as thousands of other readers all over the world. This abridged edition consists largely of complete chapters (with all their illustrations) on topics which have attracted the most discussion and debate, including Lyell's core theoretical principles, seminal analyses of evolution and ecological issues, and novel techniques for reconstructing the past. It thus makes freshly available one of the master works of the nineteenth century.

This volume is part of the definitive edition of letters written by and to Charles Darwin, the most celebrated naturalist of the nineteenth century. Notes and appendixes put these fascinating and wide-ranging letters in context, making the letters accessible to both scholars and general readers. Darwin depended on correspondence to collect data from all over the world, and to discuss his emerging ideas with scientific colleagues, many of whom he never met in person. The letters are published chronologically: Volume 21 includes letters from 1873, the year in which Darwin received responses to his work on human and animal expression. Also in this year, Darwin continued his work on carnivorous plants and plant movement, finding unexpected similarities between the plant and animal kingdoms, raised a subscription for his friend Thomas Henry Huxley, and decided to employ a scientific secretary for the first time - his son Francis.

'I have always maintained that, excepting fools, men did not differ much in intellect, only in zeal & hard work; and I still think there is an eminently important difference'. Throughout 1869, Darwin continued to collect data for his two most significant books after Origin: The Descent of Man and Expression of the Emotions. Explorers, diplomats, and missionaries all over the world were politely encouraged to investigate, for example, how emotions such as surprise, anger and shame were expressed in different cultures. As Darwin's research on human evolution neared completion, he learned that Alfred Russel Wallace, the co-discoverer of the theory, had begun to raise questions about its application to certain aspects of human development, attributing these to the action of a 'higher power'. In his correspondence, Wallace alluded to his belief in spiritualism, which he fully believed to be open to scientific investigation, but which gave Darwin much pause.

This volume is part of the definitive edition of letters written by and to Charles Darwin, the most celebrated naturalist of the nineteenth century. Notes and appendixes put these fascinating and wide-ranging letters in context, making the letters accessible to both scholars and general readers. Darwin depended on correspondence to collect data from all over the world and to discuss his emerging ideas with scientific colleagues, many of whom he never met in person. The letters are published chronologically: volume 20 includes letters from 1872, the year in which The Expression of the Emotions in Man and Animals was published, making ground-breaking use of photography. Also in this year, the sixth and final edition of On the Origin of Species was published and Darwin resumed his work on carnivorous plants and plant movement, finding unexpected similarities between the plant and animal kingdoms.

This pivotal volume in the definitive edition of Charles Darwin's letters covers the year 1871, the year in which Descent of Man, Darwin's first public statement on human evolution, was published. The large number of letters in this year - more than 800 - reflects the excitement this caused. Darwin depended on correspondence to collect data from a growing network of contacts all over the world and to discuss his emerging ideas with colleagues, many of whom he never met in person. This year also saw the marriage of Darwin's daughter Henrietta, the first of his children to marry; the volume includes her personal journal of the year, published here for the first time, which complements letters that hint at her important role in her father's work as both commentator and editor. Notes and appendixes put these fascinating and wide-ranging letters in context, making them accessible to both scholars and general readers.

During 1867 Darwin intensified lines of research that were to result in two important publications, Descent of Man and Selection in Relation to Sex and Expression of the Emotions in Man and Animals. Darwin circulated a questionnaire on human expression, asking his established contacts to pass it on to their acquaintances, with the result that he began to receive letters from an even more diverse and far-flung network of correspondents than had previously been the case. Convinced that human descent was strongly influenced by sexual selection, he also started to ask his correspondents about sexual differences in animals and birds. At the same time, he was working on the proof-sheets of another major work, Variation of Animals and Plants under Domestication, while negotiating almost weekly with French, German, and Russian translators. For information on the Charles Darwin Correspondence Project, see http: //www.lib.cam.ac.uk/Departments/Darwin.