Darwin’s work on insectivorous plants began by accident. While on holiday in the summer of 1860, staying with his wife’s relatives in Hartfield, Sussex, he went for long walks on the heathland and became curious about the large number of insects caught by the common sundew (Drosera rotundifolia). He reported to his friend Joseph Dalton Hooker: ‘I amused myself with a few observations on the insect-catching power of Drosera; & I must consult you some time whether my “twaddle” is worth communicating to Linnean Soc.’ Although he continued to think of his studies of carnivorous plants as a guilty pleasure, this encounter began a long-running research project that showed some of the connections between plants and animals.

Darwin published four volumes on barnacles, the crustacean sub-class Cirripedia, between 1851 and 1854, two on living species and two on fossil species. Written for a specialist audience, they are among the most challenging and least read of Darwin’s works and are often dismissed as a necessary detour on the road to the development of the theory of evolution through natural selection. These volumes reveal, in fact, how observation, experiment, and classification both informed and were informed by Darwin’s species theory. Every aspect, from the choice of subject to the production of the volumes, reveals something about Darwin’s approach to scientific investigation. While appearing to conform to long-established practice, Darwin introduced a new approach to systematics that challenged the purely morphological methodology of his predecessors.

Earthworms were the subject of a citizen science project to map the distribution of earthworms across Britain (BBC Today programme, 26 May 2014). The general understanding of the role earthworms play in improving soils and providing nutrients for plants to flourish can be traced back to the last book Darwin wrote, snappily-titled 'The formation of vegetable mould through the action of worms with observation on their habits', which was published in 1881. Despite Darwin’s fears that a book on earthworms might prove a failure, it became a best seller.

Darwin's daughter Henrietta kept a diary for a few momentous weeks in 1871. This was the year in which Descent of Man, the most controversial of her father's books after Origin itself, appeared, a book which she had helped him write. The small lockable volume records her thoughts on attending an Anglican mission organised by one of her father's critics, her own inclination to thoughtful scepticism, and her intimate reflections on the consequences of her father’s theories for religious belief. This was also the year in which, within the space of three months, she met and married her husband, Richard Litchfield: the intensely personal and deeply reflective journal entries from July cover the period of their courtship.

Between March and November 1868, while Darwin was researching his book The Expression of the Emotions in Man and Animals, he showed a succession of visitors a set of photographs of human faces, some with the muscles artificially contracted by electric probes, and asked them what emotion they thought the photographs conveyed. Darwin’s research has striking parallels with contemporary facial recognition experiments. We have recreated Darwin’s expression experiment online, using 21st century techniques to study many of the same problems that Darwin was interested in, using the same photographs Darwin used more than 100 years ago. Try the emotion experiment for yourself.

Charles Darwin’s observations on the development of his children, began the research that culminated in his book The Expression of the emotions in man and animals, published in 1872, and his article ‘A biographical sketch of an infant’, published in Mind in 1877. As early as 1839 Darwin had begun to collect information on the behaviour of infants from his relatives with young families. However, it was Darwin’s personal experience of fatherhood that was central to his formulation of the questions he was to pursue regarding the nature of the expression of emotions. He closely observed the development of his first child, William Erasmus, the stages of his development suggesting to Darwin those expressions which are instinctive and those which are learned. This research was ultimately directed towards showing that the physiological expression of the emotions in humans was no different in kind from that exhibited by animals.

Darwin became increasingly involved in botanical experiments in the years after the publication of Origin. The building of a small hothouse - a heated greenhouse - early in 1863  greatly increased the range of plants that he could keep for scientific investigations, in particular tropical plants for his experiments into their sensitivity to touch. He was persuaded to build it - an expensive undertaking - by a neighbour's gardener who had been helping Darwin use his employer’s hothouses over the previous two years.  Darwin enjoyed looking through plant catalogues and making lists of exotic specimens with which to stock the hothouse, and it proved so valuable, and the work so engrossing, that in the end he built a complex of greenhouses capable of sustaining a wide range of species.

Honeycombs are natural engineering marvels, using the least possible amount of wax to provide the greatest amount of storage space, with the greatest possible structural stability. Darwin recognised that explaining the evolution of the honey-bee’s comb-building abilities was essential if his theory of natural selection was to be taken seriously, and in the 1850s he carried out his own experiments at his home at Down House in Kent, and exchanged many letters on the subject. One correspondent even drew an ingenious analogy with a plum pie - you can try this at home!

The story of Charles Darwin’s involvement with the church is one that is told far too rarely. It shows another side of the man who is more often remembered for his personal struggles with faith, or for his role in large-scale controversies over the implications of evolutionary theory for religion. His local activities in the village of Down paint a fascinating picture of a man who, despite his own divergent beliefs and uncertainties, was determined to support the church as a social institution. His correspondence provides a unique window into this complicated relationship throughout Darwin’s life, as it reveals his personal and professional interactions with various clergymen and religious bodies.

The years 1858 and 1859 were, without doubt, the most momentous of Darwin’s life. From a quiet rural existence filled with steady work on his ‘big book’ on species, he was jolted into action by the arrival of an unexpected letter from Alfred Russel Wallace. This letter led to the first announcement of Darwin’s and Wallace’s respective theories of organic change at the Linnean Society of London in July 1858 and prompted the composition and publication, in November 1859, of Darwin’s major treatise On the origin of species by means of natural selection. By the end of 1859, Darwin’s work was being discussed in publications as diverse as The Times and the English Churchman, and Darwin himself was busy as never before: answering letters, justifying and explaining his views to friends, relations, and ‘bitter opponents’. The correspondence shows vividly just how distressed Darwin was during the days leading up to the Linnean meeting. On 18 June 1858, his eldest daughter, Henrietta Emma,  was stricken with diphtheria, then a little-known and frightening illness. Several days later, their 18-month-old baby, Charles Waring, came down with scarlet fever. His condition deteriorated rapidly in the space of a few days and the Darwins were shocked by his unexpected death on 28 June.