The dispersal of the banana across the Pacific was mentioned earlier in this blog. A list of 36 plants of American origin has been compiled, mostly by Thor Heyerdahl, that supposedly were diffused into the Pacific and/or Asia in pre-Columbian times.
Firm evidence for all 36 plants is lacking but about seven stand out as good candidates:
Sweet potato (Ipomoea batatas)
Bottle gourd (Lagenaria)
Chili pepper (Capsicum)
Of these seven, the sweet potato and bottle gourd are considered as established examples although there is argument on whether the diffusion was brought about by humans or by natural dispersal.
The sweet potato in particular has been the subject of continuing controversy and debate among scholars. The strongest evidence for a human diffusion of sweet potato cultivation comes in the very similar words used for the plant in the Pacific and in South America.
The words are of the "kumara" form. The two main arguments against the linguistic evidence are that the supposed cognates to this word in South America do not occur along the coast, and that Pacific varities of kumara appear related more to current Mexican rather than Ecuadorian or Peruvian varieties.
However, there is no doubt that the kumara cultivation praticed over wide areas of Pacific is related as are the words for the sweet potato. In other words, someone started cultivating sweet potatoes either independently or by transmission and then spread the practice around so that it stretched from eastern Polynesia to New Guinea. There is also some evidence that sweet potatoes may have been found in the Marianas and the Philippines in pre-Columbian times. Pigafetta mentions them in both places during Magellan's voyage around the world.
That the sweet potato would become such an important cultigen independently on both sides of the Pacific and also have a coincidentaly similar name seems rather unlikely to me. If we assume that Austronesians had contact with both Incans and Mesoamericans, it could be that the actual name and species were borrowed from separate but still American sources.
Paul Kekai Manansala
Jon Hather & P.V.Kirch, "Prehistoric sweet potato (Ipomoea batatas) from
Mangaia Island, Central Polynesia". Antiquity 65:887-93 (1981).
Some interesting internet discussion on the subject between Yuri Kuchinsky and Ross Clark can be found at: http://www.trends.net/~yuku/tran/8p2.htm
Abstract from 21st Annual Northeast Conference on Andean Archaeology and Ethnohistory
Trans-Pacific Contact in the Ecuadorian Gulf of Guayaquil? Richard Scaglion (Univ. Pittsburgh) & Maria - Auxiliadora Cordero (Univ. Pittsburgh) Recent research in the Cook Islands has established that the sweet potato, a new world cultivar, was introduced into Polynesia by AD 1000. But how did it get there? Although several methods of dispersal without human agency are plausible, what seems to have
sparked the imagination of many researchers is the possibility of trans-Pacific contact. One of the stronger lines of evidence suggestive of possible human agency in the diffusion of the sweet potato from the new world into Polynesia is the often-mentioned resemblance in certain terms for the cultivar: the word cumar, similar to the Polynesian kumara, has been reported from the highlands of Ecuador.
This paper reviews literature establishing that cumar (in the form comal and/or cumal) was a term used by the Caari people of Ecuador, who were sweet potato cultivators. It further weighs evidence suggesting that Pre-Inkan Caari territory stretched from the Andes to the Ecuadorian coast on the eastern margins of the Gulf of Guayaquil, thus contradicting Brand's (1971:363) dictum that "What is absolutely
definite, is that nowhere on the Ecuadorian or Peruvian coast was there a people cultivating any kind of sweet potato under a name even remotely resembling cumar or cumara." Implications of this finding are discussed, and possible evidence for trans-Pacific contact is reconsidered.