David Lack, FRS (1910-1973) has been called Britain's most influential ornithologist. Amongst other achievements he developed what is now known as Lack's Principle which explained the evolution of avian clutch sizes in terms of individual selection as opposed to the competing contemporary idea that they had evolved for the benefit of species (also known as group selection); this has been considered a major development in Darwinian evolution His pioneering life-history studies of the living bird helped in changing the nature of ornithology from what was then a collection-oriented field. He was a longtime director of the Edward Grey Institute of Field Ornithology at the University of Oxford.