He made advances in ecological and population genetics in lepidopterans, pulmonate land snails and humans.
In medical genetics, he worked with Cyril Clarke on Rh disease.
[1] Cyril Clarke answered an advert in an insect magazine for swallowtail butterfly pupa that had been placed by Sheppard.
They met and began working together in their common interest of lepidopterology.
In 1961 Sheppard started a colony of scarlet tiger moths by the Wirral Way, West Kirby, Merseyside, which were rediscovered in 1988 by Cyril Clarke, who continued to observe them in his retirement to study changes in the moth population.