A fast yam to Polynesia: New thinking on the problem of the American sweet potato in Oceania

Abstract

This essay revisits Leach’s thesis that American sweet potato (Polynesian kūmara) was first introduced into the Pacific as a variation on Dioscorea yam by Polynesian voyagers returning from South America. A review of early agricultural systems on both sides of the first transoceanic kūmara transfer clarifies South American disinterest in Polynesian cultigens, but not necessarily why sweet potato was transferred to Oceania as a lone, yam-like root crop. Archaeologists working on Rapa Nui and northern South Island (New Zealand) have identified early kūmara cultivation in dry soil planting pits that conform to a widespread Oceanic yam agronomy. Historical ethnobotany sources from Hawai‘i reinforce a Polynesian pattern of kūmara production in three to six months from planting pits and mounds, compared to nine months or more for yam. Northern South Island evidence also confirms that the planting pit method could provide for kūmara cultivation in free-draining soils of low to medium fertility in a climate where yam would not grow. I propose a model in which Polynesians selected South American kūmara for transoceanic transfer as a fast growing, hardy survival yam. These versatile kūmara qualities may even have encouraged the lasgreat voyages of Oceanic exploration to remote southern Polynesia.