Roger Shepherd Duff, CBE FRSNZ (11 July 1912 – 30 October 1978) was a New Zealand ethnologist and museum director.
Duff was born in Invercargill, Southland, New Zealand in 1912. He is the son of Oliver Duff and helped raise his nephew, writer Alan Duff. He started work at Canterbury Museum in 1938 and became its director ten years later. Duff excavated skeletons of moa, an extinct flightless bird, at Pyramid Valley in north Canterbury and at the Wairau Bar in Marlborough.
Duff brought proof through his scientific papers of the existence of Moa-hunters as an early and distinct form of Māori culture. He developed and defended one of three major theories as to the origins of the Polynesian people: he believed, on the basis mainly on the physical differences, that the ancestors of the Polynesians could not have come from Asia via the Melanesian island. His main idea was that they had moved south from the area around Taiwan, through the Micronesian islands (mainly coral attols) to Fiji, Tonga and Samoa. From here they radiated out into the Pacific through Tahiti and the Society Islands: north and east to Hawaii; east and south to reach the Marquesas and Easter Island, and south and to the West to New Zealand.
He was highly critical of the hypothesis of American origins promoted by Thor Heyerdahl which was popularised by the voyage of the Kon Tiki Over the years with accumulation of evidence (both pro and contrary) these three theories have all been modified to various degrees, but no one hypothesis has ever found universal acceptance.