William & Mary

The ancient Anthropocene, the mystery of the sweet potato, and how bananas became seedless

  • William & Mary archaeologist Jennifer Kahn examines artifacts from one of her numerous excavations of human sites in the islands of Oceania.
    Island focus:  William & Mary archaeologist Jennifer Kahn examines artifacts from one of her numerous excavations of human sites in the islands of Oceania. Kahn contributed knowledge from Hawaii, Micronesia and Polynesia to a synthesis paper in “Science” that challenges the traditional notion of the Anthropocene.  Photo by Stephen Salpukas
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The Anthropocene isn’t something new, or even recent. Large-scale environmental change began when our ancestors started agriculture; Earth entered an anthropogenic stage 3,000 years ago or even earlier.

That’s the consensus of a group of more than 250 archaeologists presented in a paper, “Archaeological assessment reveals Earth’s early transformation through land use,” published this week in the journal Science. The findings challenge “the emerging Anthropocene paradigm that large-scale anthropogenic global environmental change is mostly a recent phenomenon.”

Jennifer Kahn, an associate professor in the William & Mary Department of Anthropology, is a co-author on the paper, a synthesis that brought together contributions of 250 of her fellow archaeologists who work all over the globe. The ArchaeoGLOBE project documents the 10,000 years of transformation of the earth by food-cultivation methods.

“The take home message — that the Anthropocene is longer than many historical models suggest — is really an archaeology success story,” Kahn said.

She pointed out that part of the business of archaeology is to track change in people-plants-animals-landscapes through time — lots and lots of time. By contrast, scientists and scholars in disciplines that have formed the common concept of the Anthropocene often have set the period’s genesis at the Industrial Revolution. She gave an example of ecologists who study climate change and resource exploitation through fisheries, using a “starting point” of the fish counts of 200 years ago.

“But Pacific Islanders had already been intensively fishing for some 800 years before that in Eastern Polynesia, thousands of years before that in Western Polynesia, and many thousands of years before that in  the Western Pacific,” Kahn said. “So understanding these deep human-environmental connections is important not just for modeling landscape change in the past, but for modeling it today.”

Kahn has done extensive archaeological work in the Pacific islands known collectively as Oceania. She contributed to the Science paper information on people-plant interactions for Hawaii, Polynesia, Micronesia, Melanesia, and Island Southeast Asia. It’s a region of outsized importance in the development of world food crops. Oceania is sufficiently significant to the development of agriculture that Hawaii, Polynesia, Micronesia and Melanesia all were given separate categories in the paper.

A center of plant domestication

“Not many people know that the Pacific Islands were a center of plant domestication,” she said. “Lots of folks know that cereal crops were domesticated in the Fertile Crescent, but few people know that bananas, pandanus and many tree crops with nuts were domesticated in the Western Pacific in Papua New Guinea.”

These innovative foodstuffs, together with other domesticated plants such as taro and yams, traveled east as “canoe species.” Kahn said the Pacific Islanders would carry them packed in soil-filled bamboo pots as they voyaged across the sea to new islands. But there is at least one mystery food in the Pacific: the sweet potato.

“Wild forms of sweet potato are not found in the Pacific Islands naturally, hence it was always likely that the origin spot for this plant’s domestication was going to be outside the Pacific Islands,” Kahn said. She added that the Polynesian word for sweet potato does not have any pre-Polynesian precursors, another clue that the plant came from somewhere else.

“But it’s always been a mystery, because pieces of charred sweet potatoes have been found in archaeological sites pre-dating the arrival of Europeans,” she said. “They date back to around AD 1300, and European contact in most places was not until the 1700s. Right now, we think that some Polynesians, who were excellent voyagers, probably got caught in a storm and ended up in South America.”

Wild forms of the sweet potato are found in South America, and the natives had already domesticated the plant there, she said. The new arrivals were eager to adopt the sweet potato because it was similar to their familiar yams. The same theory suggests that the Polynesians had some poultry aboard.

Leave the chicken; take the sweet potato

 “When the Polynesians wanted to go back to the islands, it seems they left the chicken for the South Americans and took the sweet potato,” Kahn said. “Sweet potato then got introduced into the Pacific Islands and became a very important crop, outstripping yams, likely because it is easier to grow and can be grown in a wider range of environments.”

Kahn explained that casual nurturing, followed by cultivation, were the first steps toward true agriculture — and the Anthropocene. Hunter-gatherers began encouraging growth of tasty wild plants, “perhaps by transplanting them closer to their residence, or weeding, or sowing, but then doing little afterwards.”

“Agriculture is much more intensive,” she said. “Agricultural crops were genetically modified by generations of human-plant interactions. These types of crops often have to be intentionally propagated by seed or by cuttings. During this process farmers selected for larger fruits and seeds that had thicker skins that would not shatter, such that domesticated plants are considered genetically altered from their wild ancestors.”

A good example of the domestication of a wild plant is the coconut. Kahn said people began to plant wild coco fruit near their homes. Artificial selection results from decades of the planter and their descendants selecting the larger, more choice, offspring to nurture.

“The larger the fruit, the more coconut meat and the more coconut water. Thus, domesticated coconuts have much larger fruits than wild ones,” she explained. “The water is super yummy and nutritious, by the way.”

Coconut agriculture became pretty sophisticated pretty early, she said. The islanders had their own version of the Native American “three sisters” of squash, beans and corn.

“Intensive coconut agriculture in the past would have been tree cropping, with coco at the top, breadfruit mid-story and things like sugar cane and taro underneath,” Kahn said.

Agriculture = tillage = transformation of landscapes

And agriculture, even in societies that don’t have metal tools, means systematic soil tillage and, ultimately, transformation of landscapes through clearing and planting. But Kahn cautions that it’s not always easy to look into the archaeological record and draw lines that separate gathering from cultivation and cultivation from agriculture.

“It used to be that we thought cultivation always led to agriculture,” she said. But now the line is known to be blurrier. Kahn pointed to a plant called fei, or mountain plantain, a foodstuff of the Ma’ohi, ancestors of present day Tahitians living in the Society Islands of French Polynesia.

“At the time of European contact, fei appear to have been semi-cultivated,” she said. “These plants grow wild in the mountains, but the Ma'ohi likely transplanted some communities into easier-to-reach locales.”

But Kahn said the archaeological record seems to show that fei cultivation wasn’t sustained. Serious cultivation of fei would reveal itself in a number of ways, including fei bearing bigger fruits as the plant became domesticated. The Ma’oni seemed to eat fei as a special food or as famine fare, and so fei became an outlier in the record of food husbandry.

Fei may not have caught on as an agricultural crop, but bananas, their cousins, are a different story. Kahn explained that bananas, like most Polynesian crops, are vegetatively propagated. “This means you plant part of a plant, not a seed,” she explained. Generations upon generations of Oceania banana farmers bred seeds out of bananas by artificially selecting specimens that had smaller and smaller seeds for vegetative propagation.

“So you’ll see those little black dots when you eat a banana,” Kahn said. “Those are remnant seeds — not viable for planting.”