Between 1851 and 1855, Darwin published a series of four monographs on the cirripedes (barnacles), two on the living Cirripedia (1852, 1854) and two on fossil Cirripedia (1851, 1855). This study consumed eight years of his life, from 1846 to 1854. Sandwiched between penning early drafts of his species theory in 1842 and 1844 (Darwin 1909) and the publication of Origin of Species in 1859, the barnacle monographs have been interpreted as delaying Darwin’s work on his theory of evolution. It is clear, however, that the study of the barnacles complemented Darwin’s earlier preoccupation with invertebrate biology and served to bolster his confidence in his species theory (Sloan 1985; A. C. Love 2002). He gained from this study clarity on points important to his evolutionary theory (the significance of variation, homology, and embryology as keys to affinity, change of function, and the evolution of novelty), as well as significant empirical support that would feature in Origin. In addition, his receipt of the Royal Medal of the Royal Society of London in 1853, largely on the basis of his first barnacle volume, gained him widespread recognition as a naturalist of high standing. Coupled with his earlier geological studies, the barnacle monographs reinforced Darwin’s scientific reputation. His credentials were thus impeccable prior to publishing a theory of evolution that would attract protracted and vociferous criticism among naturalists and laymen alike.

To be sure, Darwin’s barnacle monograph was a significant achievement in its own right. Indeed, despite some errors in interpretation, it remains an important work in cirripede morphology and systematics to this day (Southward 1987; Newman 1987, 4). Certainly it was solidly within the tradition of mid-nineteenth-century natural history. Taxonomy – the grouping and classification of organisms – was a major preoccupation of nineteenth-century naturalists. Botanists and zoologists, following the model set by Carl von Linné (Linnaeus) (1707–78), had long strived to catalog nature’s vast array of species, exponentially expanded in the early nineteenth century by the voyages of exploration such as that of the Beagle. Naturalists thus employed a hierarchical approach of dividing plant and animal kingdoms into rational categories – orders, classes, genera, and species – using the Linnaean binomial system of naming the genus and species (R. A. Richards 2009). But the aim was not simply to turn the natural world into a museum. Taxonomy formed a prominent pillar within the particularly British tradition of natural theology – a way to illustrate in the “Great Chain of Being” the order of nature reflecting the design of the Creator.