William Elford Leach

William Elford Leach FRS (2 February 1791 – 25 August 1836) was an English zoologist and marine biologist.

Elford Leach was born at Hoe Gate, Plymouth, the son of an attorney. At the age of twelve he began a medical apprenticeship at the Devonshire and Exeter Hospital, studying anatomy and chemistry. By this time he was already collecting marine animals from Plymouth Sound and along the Devon coast. At seventeen he began studying medicine at St Bartholomew's Hospital in London, finishing his training at the University of Edinburgh before graduating MD from the University of St Andrews (where he had never studied).

From 1813 Leach concentrated on his zoological interests and was employed as an 'Assistant Librarian' (what would later be called Assistant Keeper) in the Natural History Department of the British Museum, where he had responsibility for the zoological collections. Here he threw himself into the task of reorganising and modernising these collections, many of which had been neglected since Hans Sloane left them to the nation. In 1815, he published the first bibliography of entomology in Brewster's Edinburgh Encyclopedia (see Timeline of entomology – 1800–1850). He also worked and published on other invertebrates, amphibians, reptiles, mammals and birds. and was the naturalist who separated the centipedes and millipedes from the insects, giving them their own group, the Myriapoda. In his day he was the world's leading expert on the Crustacea and was in contact with scientists in the United States and throughout Europe. In 1816 he was elected a Fellow of the Royal Society at the age of 25.

However, in 1821 he suffered a nervous breakdown due to overwork and became unable to continue his researches. He resigned from the museum in March 1822 and his elder sister Jane took him to continental Europe to convalesce. They lived in Italy and (briefly) Malta and he died from cholera in San Sebastiano Curone, near Tortona, north of Genoa, on 25 August 1836.

In 1837 Dr Francis Boott, secretary of the Linnean Society of London, wrote, "Few men have ever devoted themselves to zoology with greater zeal than Dr Leach, or attained at an early period of life a higher reputation at home and abroad as a profound naturalist. He was one of the most laborious and successful, as well as one of the most universal, cultivators of zoology which this country has ever produced."

Despite his expertise in particular animal groups, Leach's greatest contribution was his almost single-handed modernisation of the whole of British zoology following its stagnation during the long war with post-revolutionary and Napoleonic France.

In Britain zoologists remained committed to the system of animal classification introduced by Linnaeus in the middle of the 18th century. This was a powerful tool but its principles led to artificial groupings of species when creating larger groups such as genera and families. For example, Linnaeus had called all animals encased in a hard outer skeleton, insects. He therefore grouped butterflies with lobsters, scorpions, spiders and centipedes but these animals are not otherwise similar in appearance, do not live in the same environment, and do not behave in the same way. The grouping does separate animals with hard outer skeletons from jellyfish, worms, snails, vertebrates, etc. but does not produce a group 'Insecta' with clear similarities shared by all its members.

In continental Europe in the late 18th century naturalists began to revise the way they grouped species. They used a wider array of characters, not just one or two, and began to discern groups of species that physically resembled one another, lived in similar ways and occupied similar habitats. They created new genera to house these coherent groups and referred to these as 'natural genera'. They named this approach the 'natural method' or 'natural system' of classification.