Asian Yams
This piece appeared on my Patreon account way back in 2022. I thought I’d move it here so that it would be more accessible.
As I mentioned in the last post, human beings aren’t particularly picky when it comes to naming edible tubers, corms, and roots. Herbs and spices are often distinguished from one another with some care, and people often seem happy to adopt words from other languages to refer to them — but roots and tubers end up conflated by broad generic names. This seems to be a general principle of human folk botany/horticulture, and there may be no better illustration of it than the English word ‘yam’.
In American English ‘yam’ almost always refers to sweet potatoes (Ipomoea batatas), which come from the Americas. The sweet potato was domesticated in either South or Central America — there are early Holocene radiocarbon dates for sweet potato remains from both regions — and it was distributed across much of tropical and subtropical America, and even out into Polynesia, before the Columbian exchange. Pace the common modern American English usage, however, the sweet potato is not actually a yam (Figure 1). (Nor is it actually a potato, but that’s another matter.)
True Yams
True yams are plants in the genus Dioscorea — an entirely different genus. Yams and sweet potatoes can be remarkably similar in flavour profile (both are nutty/earthy, though true yams aren’t quite as sweet) and in the orange and purple colouration of the flesh of varieties of both (Figure 2 below), but they are in quite different branches of the tree of life: yams are monocots and sweet potatoes eudicots, and they are thus about as distinct from one another as flowering plants (angiosperms) can be.
Yams are far more diverse than sweet potatoes, too. The genus Dioscorea includes several edible species distributed across tropical Afro-Eurasia and Australia. Some of these species were domesticated thousands of years ago, while others were/are foraged and not truly domesticated (as with the Australian species, D. hastifolia). Some produce large underground roots, some produce aerial tubers that appear above ground, and some produce both depending on the variety being grown. Some are toxic if not prepared properly. There are even some American species of Dioscorea, including the so-called ‘wild yam’ (D. villosa), found as far north as Ontario. Broadly speaking, though, cultivated true yams can be divided into African and Asian camps. West Africa, the Philippines, and New Guinea appear to have been the main centres for prehistoric yam domestication.
The principal African yam is Dioscorea cayenensis, while the Asian yams include D. alata, D. esculenta, D. hispida, and D. bulbifera. Some of the Asian yams were domesticated in New Guinea, others were domesticated elsewhere in island Southeast Asia, and some were domesticated more than once in different locations. To make matters more confusing, several species of Asian yam were introduced to Africa around 2,500 years ago by speakers of Austronesian/Malayo-Polynesian languages from Southeast Asia, so in some areas both African and Asian yams are cultivated together.
*qubi
Although Austronesian-speaking people are known to have domesticated some plant species and to have had a hand in spreading others, including Asian rice (Oryza sativa), it should be noted that yams weren’t actually domesticated by Austronesian speakers. Yams were almost certainly being cultivated in the Philippines when the first Austronesian speakers arrived from the north. There is no word for ‘yam’ in proto-Austronesian, the ancestor of the Austronesian languages, which was probably spoken on the island of Taiwan a little over four thousand years ago. The words for yams in Austronesian languages only go back as far as proto-Malayo-Polynesian, the ancestor of nearly all the Austronesian languages spoken outside Taiwan; *qubi is the relevant protoform.
In Old Javanese, yams were known as huwi or uwi, from proto-Malayo-Polynesian *qubi. We tend to think of Javanese cuisine as based on rice, but in the Middle Ages roots and tubers may have comprised a more significant part of the diet, as they still did into the twentieth century among the poor. A line in the fascinating fifteenth-century spiritual work Tantu Panggĕlaran mentions both yams and taro (text from Pigeaud’s edition [1926:71], translation from the new English version, Threads of the Unfolding Web, by Stuart Robson and Hadi Sidomulyo [2021:19]):
Uwi talĕs ḍinaharnira.
‘He ate yams and taro.’
The Malay/Indonesian word ubi, also from *qubi, now refers to both yams and sweet potatoes, as in English, and this is also the case with reflexes of *qubi in some other languages. Manioc (Manihot esculenta), another American species, is also sometimes referred to as a type of ubi in Malay/Indonesian (ubi kayu ‘wood yam’, a synonym of singkong). Otherwise, though, *qubi’s descendants usually refer to true Dioscorea yams.
Yams in New Guinea
Dioscorea alata, the most economically important and widespread Asian yam, was probably first domesticated in the highlands of New Guinea around nine thousand years ago or so, long before any Austronesian speakers got to the island. This is apparent from remains found at Kuk Swamp, a UNESCO World Heritage Site in Papua New Guinea known for the evidence it provides of extremely early agriculture involving yams, bananas (Musa spp.), and sugarcane (Saccharum officinarum), all apparently domesticated locally. D. alata tubers can grow to astounding sizes — nearly four metres (twelve feet) long in some extreme cases — and they are still important crops in the New Guinea Highlands, although the introduction of the sweet potato in the eighteenth century meant that true yams have been supplanted in many areas, at least as foodstuffs.
Yams still play significant ritual roles in New Guinea, however. This is true even in areas where yams make up a tiny proportion of consumed calories, as in Kwoma-speaking villages in the Washkuk Hills along the Sepik River in Papua New Guinea (Figure 3). Sago is the staple there. The Australian anthropologist Ross Bowden, who conducted ethnographic fieldwork in the region over many years, estimated that yams accounted for under 5% by weight of food consumed by an average person in an average day, but they were nonetheless the focus of elaborate ritual, with much of Kwoma art and culture dedicated to the fertility rites that accompanied the planting of the yam.
This may attest to the antiquity of yam cultivation in the region, and perhaps to the earlier economic importance of yams relative to other cultivated plants. It’s interesting either way.
D. alata before 1492
In any case, Dioscorea alata, the variety so important in Kwoma art and society, was one of the most widely distributed foodstuffs in the pre-Columbian world. It was grown and eaten as far to the east as Rapa Nui (Easter Island) and as far to the south as Aotearoa (New Zealand) — in both Rapa Nui and Māori it’s called uhi, from *qubi — and to this day it is the second most common yam in tropical Africa (Figure 4). It’s hard to think of other cultivated plants propagated quite as far across the Earth’s surface as that.
Unassuming tropical staples like taro and yams don’t come up often in discussions of the world before modernity. They aren’t part of the popular medieval imaginary. They are unfamiliar to many people in the global north — where academic research budgets are biggest and where the most powerful academic institutions are based — and when they aren’t unfamiliar they are often confused with American crops like sweet potatoes. This state of neglect is unwarranted. If you really want to understand the world before the great change brought about by Columbus’s first voyage in 1492, you have to get to know the humble yam.
A. J. West — Lisbon, 2022 (posted here 2024).
