Somehow
the sweet potato traveled during prehistoric times, and realistically
that means in the preceding thousand years at least and possibly much
earlier. Actual direct contact as per Thor Heyerdahl is possible but
seems unlikely. I am more inclined to take advantage of the Bronze
Age sea based global polity formed between 3,000 BC and 1000 BC.
I
have no doubt that plenty of plants were tested in new locales but I
also know that few succeeded from the resulting anomalies. Global
agriculture was still a rarity. Local prospects generally remained
local. Thus it was limited to a handful of plants such as the
coconut, cotton, amaranth and totoro reed that could survive the
tropics and prolonged exposure to wetting. Someone really had to
want to do it and make the trip in a world in which the traders did
not actually colonize that much.
From
this perspective, the sweet potato is a natural.
Sweet potato DNA
indicates early Polynesians traveled to South America
January 22, 2013 by
Bob Yirka
Prehistoric and
historical dispersal of sweet potato in Oceania, as postulated by the
tripartite hypothesis. Credit: (c) PNAS, DOI: 10.1073/pnas.1211049110
(Phys.org)—A
French based research team has found DNA evidence in sweet potato
samples that suggests that early Polynesian explorers visited South
America. Those early explorers, the researchers write in their paper
published in the Proceedings of the National Academy of
Sciences, brought the sweet potato back with them when they returned
from their long voyages.
Tracing the history of
agricultural products is one way scientists track the migration of
people during times when no written records were left behind to offer
clues. In this new effort, researchers have been investigating the
likely path of the sweet potato. First domesticated in the Andes
in South America, approximately 8000 years ago, the tuber has since
that time migrated to virtually every habitable part of the planet.
Sweet potatoes are highly nutritious and easy to grow and because of
that their introduction into various societies has had a dramatic
impact. But how they got from South America to different parts of the
world has been a mystery, though there have been several competing
theories. One of the most compelling suggested the idea of a
"tripartite" migration path, which means it came in three
different ways. Now, new DNA research appears to back up
this idea.
Initial DNA
analysis done on sweet potato samples found in several locations
around the world revealed that its history is varied and cloudy at
best, with several varieties mixing to create a mish-mash that
doesn't provide many answers. To help clear things up, the
researchers sampled specimens brought back by early explorers such
asJames Cook. In so doing, they found that the DNA
evidence indicated that the sweet potato had migrated to
Polynesia long before European explorers had made their way to that
part of the world. That meant that the Polynesians had to
go get it themselves or it got there some other way, such as via
seeds carried in the wind, aboard natural rafts etc. But because
scientists have already uncovered proof that Polynesian sailors made
it as far as the Easter Islands, it seems plausible to envision they
extended their reach to mainland South America as well.
The DNA evidence also
showed that another two lines came about as a result of European
exploration – originating from South America to Europe and then on
to other parts of the world. In the first wave, the sweet potato was
carried to the western Pacific, in the second it was carried to the
Philippines. Both resulted in further sweet potato migration to their
respective parts of the world.
More
information: "Historical collections reveal patterns of
diffusion of sweet potato in Oceania obscured by modern plant
movements and recombination," by Caroline Roullier, Laure
Benoit, Doyle B. McKey, and Vincent Lebot, PNAS,
2013.www.pnas.org/cgi/doi/10.1073/pnas.1211049110
Abstract
The history of sweet potato in the Pacific has long been an enigma. Archaeological, linguistic, and ethnobotanical data suggest that prehistoric human-mediated dispersal events contributed to the distribution in Oceania of this American domesticate. According to the "tripartite hypothesis," sweet potato was introduced into Oceania from South America in pre-Columbian times and was then later newly introduced, and diffused widely across the Pacific, by Europeans via two historically documented routes from Mexico and the Caribbean. Although sweet potato is the most convincing example of putative pre-Columbian connections between human occupants of Polynesia and South America, the search for genetic evidence of pre-Columbian dispersal of sweet potato into Oceania has been inconclusive. Our study attempts to fill this gap. Using complementary sets of markers (chloroplast and nuclear microsatellites) and both modern and herbarium samples, we test the tripartite hypothesis. Our results provide strong support for prehistoric transfer(s) of sweet potato from South America (Peru-Ecuador region) into Polynesia. Our results also document a temporal shift in the pattern of distribution of genetic variation in sweet potato in Oceania. Later reintroductions, accompanied by recombination between distinct sweet potato gene pools, have reshuffled the crop's initial genetic base, obscuring primary patterns of diffusion and, at the same time, giving rise to an impressive number of local variants. Moreover, our study shows that phenotypes, names, and neutral genes do not necessarily share completely parallel evolutionary histories. Multidisciplinary approaches, thus, appear necessary for accurate reconstruction of the intertwined histories of plants and humans.
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