How do new species arise? This was the ancient question that Charles Darwin tackled soon after returning to England from the Beagle voyage in October 1836. Darwin realised a crucial (and cruel) fact: far more individuals of each species were born than could possibly survive.

Darwin experienced his first earthquake in 1834, but it was a few months later that he was really confronted with their power. Travelling north along the coast of Chile, Darwin and Robert FitzRoy, captain of HMS Beagle, were confronted with a series of violent natural events that they were perfectly placed to study.

This speciallycommissioned BBC Radio drama is based entirely on Charles and Emma Darwin's own words and correspondence. Behind the controversial public persona, Darwin was an affectionate family man, fully engaged - sometimes heartbreakingly so - in the lives of his wife, Emma and their children.

For all his working life, Darwin used letters as a way both of discussing ideas and gathering the 'great quantities of facts' that he used in developing and supporting his theories. They form a fascinating collection from many hundreds of correspondents, containing diagrams and drawings, personal observations, photographs, and even specimens.

What did Darwin really believe about God? the Christian revelation? the implications of his theory of evolution for religious faith? These questions were asked again and again in the years following the publication of Origin of species (1859). They are still asked today by scholars, scientists, students, and religious believers.

Darwin was a photography enthusiast. This is evident not only in his use of photography for the study of Expression and Emotions in Man and Animal, but can be witnessed in his many photographic portraits and in the extensive portrait correspondence that Darwin undertook throughout his lifetime. His close friend and botanist Joseph Dalton Hooker would come to call Darwin's epistolary exchange of photographic images as his "carte correspondence".

In May 1856, Darwin began writing up his 'species sketch' in earnest. During this period, his working life was completely dominated by the preparation of his 'Big Book', which was to be called Natural selection. Using letters are the main source for much of his research he amassed data, carried out breeding experiments, and struggled with statistical analysis. Several of his experiments: seeds would not germinate; beans failed to cross; newly-hatched molluscs refused to do what he hoped. Most significant in terms of Darwin's future, however, was the beginning of his correspondence with Alfred Russel Wallace.

The letters from these years reveal the main preoccupations of Darwin's life with a new intensity. The period opens with a family tragedy in the death of Darwin's oldest and favourite daughter, Anne, and it shows how, weary and mourning his dead child, Darwin persevered with his scientific work, single-mindedly committed to the completion of his barnacle research. His four-volume study was finally published after eight years of work. Darwin's professional circle was enlarged both by new friendships with noted scientists such as the physiologist Thomas Henry Huxley, and the American botanist Asa Gray, but also by contact with a network of animal breeders, nurserymen, and pigeon-fanciers.

Darwin's study of barnacles, begun in 1844, took him eight years to complete. The correspondence reveals how his interest in a species found during the Beagle voyage developed into an investigation of the comparative anatomy of other cirripedes and finally a comprehensive taxonomical study of the entire group. Despite struggling with a recurrent illness, he continued to write on geologicy, and published notes on the use of microscopes. Three more children, Elizabeth, Francis, and Leonard, were born during this period, but the death of Darwin's father in 1848 left the family well-provided for.

The scientific results of the Beagle voyage still dominated Darwin's working life, but he broadened his continuing investigations into the nature and origin of species. Far from being a recluse, Darwin was at the heart of British scientific society, travelling often to London and elsewhere to attend meetings and confer with colleagues, including the man who was to become his closest friend, Joseph Dalton Hooker. Down House was altered and extended to accommodate Darwin's growing family; and, with his father's advice, Darwin began a series of judicious financial investments to ensure a comfortable future for all those under his care.