Yams’ Domestication and Dispersal

Domestication may have begun in West Africa, where hunter-gatherers ate wild yams some 60,000 years ago.²²² Between 45,000 and 15,000 years ago, they devised stone and wooden hoes and picks to dig tubers. This work must have been difficult because yams produce edibles deeper underground than potatoes, sweet potatoes, or cassava. Where yams were in forests, people had to penetrate nearby tree roots without metal spades to access tubers. Around 9000 BCE, hunter-gatherers responded to shrinking habitats amid climate change by selecting large yams to maximize food supply. About 3000 BCE, West Africans domesticated D. rotundata and D. cayenensis. Their farming concentrated in what are today Cote d’Ivoire, Ghana, Togo, Benin, Nigeria, and Cameroon, an area known as the yam belt. Slaves from this region thus knew how to grow yams. Earlier was mentioned their familiarity with sweet potatoes. With this knowledge, they created tuber and root agriculture in the American South, whereas indigenous traditions in tropical America centered on D. trifida, sweet potatoes, and cassava and predated the slave trade. Mesoamerican yam consumption and cultivation predated the Maya. In Southeast Asia, the other Old World yam center, D. escu- lenta arose in what are today Vietnam, Laos, and Cambodia. To their west, Thais began eating wild yams between 10,000 and 7000 BCE.²²³

Around 7000 BCE, New Guineans began clearing land for yams.²²⁴ Indonesians were growing them by 5000 BCE. Yam farming spread to Melanesia roughly 3,000years later. China, acquiring yams before 2000 BCE, may have designated them medicine first and food and pig feed second.²²⁵ In the second millennium BCE, Micronesia adopted yams. The tuber reached eastern Polynesia around 1500 BCE, spreading west through its islands during the first millennium CE. One hypothesis holds that fishers harvested wild yams on island coasts, observing that discards germinated. This discovery led them to plant yams, beginning the process of domestication. In southwestern- most Polynesia, New Zealand began growing yams around 400, though consumption of wild tubers probably preceded cultivation. Yams reached India before 600.²²⁶ Throughout Southeast Asia and Oceania, they joined banana, plantain (Musa x paradisiaca), breadfruit (Artocarpus altilis), and taro as a staple.²²⁷ Separate from these developments, the Indian Ocean’s Madagascar began cultivating yams between the eleventh and fifteenth centuries.²²⁸ They were absent from the Mediterranean— including Egypt—and Arabia.

Reaching India in 1498, the Portuguese learned that Indians and Malaysians provisioned ships with yams. This practice had begun centuries earlier, allowing long voyages across the Indian and Pacific Oceans because yams’ vitamin C prevented scurvy.²²⁹ Portugal did likewise. Led by Iberia, Europeans opened their own continent, Africa, Asia, Oceania (including Australia), and the Americas to crop and livestock exchanges.

The western hemisphere’s sweet potatoes, cassava, and cacao (Theobroma cacao) competed with yams in tropical Africa and Asia. Cassava’s inexpensiveness and durability, discussed earlier, made it popular. An earlier section noted its ubiquity in African diets. Despite competition, yams continued to feed Nigeria, Cote d’Ivoire, Benin, Ghana, Togo, Zaire, Ethiopia, Chad, the Central African Republic, New Guinea, Brazil, Haiti, Jamaica, and Japan. Their expensiveness relative to sweet potatoes and cassava in Africa, Asia, Australia, New Guinea and several other equatorial Pacific islands, South America, and the Caribbean indicates strong demand. High prices in West Africa reflect low yields and perishability. In 2016, West African yam production totaled just two-fifths the cassava harvest.²³⁰

Yams’ Nutriment

On average. West Africa’s 150 million yam eaters derive over 200 calories daily from the tuber.²³¹ Among the region’s foods, yams supply fewer calories by mass than corn, cassava, or sorghum (Sorghum bicolor) and more than sweet potatoes. Carbohydrates furnish most calories. By mass, yams have more calcium than cassava and corn; more iron than cassava; more magnesium than sorghum; more phosphorus than sweet potatoes and cassava; more potassium than corn, cassava, sweet potatoes, and sorghum; more zinc than sorghum; more copper than cassava, sweet potatoes, and sorghum; more manganese than cassava, sweet potatoes, and sorghum; more selenium than sweet potatoes and sorghum; more carotenoids than cassava and sorghum; and more vitamin B, than cassava and sweet potatoes; B₅ than corn and sorghum; B₆ than cassava, sweet potatoes, and sorghum; B_q than corn, sweet potatoes, and sorghum; C than corn, sweet potatoes, and sorghum; E than cassava, sweet potatoes, and sorghum; and К than cassava, corn, sweet potatoes, and sorghum.²³² Table 13.9 shows that 100 grams of yams provide 23.3 percent DV for potassium, 20 percent for manganese, 9 percent for copper, 5.5 percent for potassium, 5.3 percent for magnesium, 28.5 percent

TABLE 13.9

Nutrients in Yams 100g

for vitamin C, 14.5 percent for vitamin B₆, 7.3 percent for B,, and 5.8 percent for B_q. No other nutrient equals or exceeds 5 percent.

Yams, Yap Island, and Australia

Yams’ nutrients and calories increased population on Yap Island—where the tuber occupied 80 percent of arable land—in the North Pacific Ocean’s western Caroline Islands.²³³ Islanders recounted overcrowding so severe that people had to live on rafts in mangrove swamps.²³⁴ Such stories may be exaggerations, though Yap was crowded when Spaniards attempted to settle it in 1731. Yams alone did not nourish Yapese, who also ate taro, breadfruit, banana, sweet potato, and coconut. As in other places where Europeans encountered indigenes, Old World diseases killed Yapese because they lacked immunity. Yams, sweet potatoes, and other foods deserve no blame for this mortality.

Health data came from Australia’s aborigines. In 1982, ten participated in a dietary experiment.²³⁵ All had imitated Europeans, consuming fatty meats, white flour, rice, potatoes, onions, sucrose, sugary beverages, and alcohol and becoming overweight and diabetic. This book absolves the potato from these problems because an earlier section detailed its contributions to nutrition and vitality. Dissatisfied with their predicament, the ten resumed hunting and gathering for 7 weeks, eating only wild produce: seafood, game, yams, figs (Ficus species), and honey. By experiment’s end, they lost 8.1 kilograms (17.9 pounds) on average, blood pressure and triglycerides declined, and diabetes’ symptoms diminished or disappeared. This outcome implies that yams benefited these indigenes, but wild foods and activity also must have invigorated them.