Pleistocene Sweet Potatoes (Ipomoea batatas)

Thanksgiving wouldn’t be complete without sweet potatoes and mashed Irish potatoes (Solanum tuberosum).  Both species originated in Central and South America, and paleo-indians were the first humans to eat them, possibly as early as 13,000 years ago.  Genetic and morphological studies suggest the sweet potato originated in the region located between the Yucatan Peninsula, Mexico and Venezuela.  The ancestor of the sweet potato is not known in the wild and may be extinct.  The modern sweet potato is likely a hybrid cross between this extinct wild ancestor and a species of morning glory (Ipomoea triloba).  Foraging humans may have gathered the sweet potato’s wild ancestor to extinction.  The oldest archaeological remnants of sweet potatoes were found in a Chilca Canyon cave.  Chilca Canyon is located near the south central Pacific coast of Peru, and it was much farther inland 10,000 years ago when paleo-indians left remains of their food here.  (At least 1 archaeologist disputes the age of this evidence.)  This region was a coastal savannah with some wooded areas then.  Remains of other species found in this cave in addition to sweet potato include Irish potato, olluca (Ullucus tuberosa), jicama (Pachyrhizos crosus), bottle gourd, and prickly pear.

Archeologists believe paleo-indians initially spread sweet potatoes and other edible plant species by accident.  All of the above mentioned plants will readily sprout from their tubers, roots, or seeds, if carelessly tossed in a garbage pile in contact with soil. By observing these accidents, paleo-indians learned to deliberately plant and care for these valuable plants when climatic conditions deteriorated and food became scarce.  Climate did become more arid along the Peruvian coast during the Holocene.  Native Americans settled near oasises located in a landscape that had transformed from savannah to desert.  Several archaeological sites in the Pampas de las Llamas region show that by 3500 BP native Americans were cultivating sweet potatoes, Irish potatoes, common bean, lima bean, oca (Oxalis tuberosa), oculla, peanuts, peppers, turban squash, avocado, edible canna (Canna edulis), cotton, bottle gourd, eggfruit (Pouteria lucuma), peanut butter fruit (Buchosia armeniaca), and manioc root.  The remains of wild game, marine mammals, and fish were also found at these sites.

Manioc root is poisonous, if not processed in a certain way.  When paleo-indians first colonized South America, they were unfamiliar with the many plants that grow in tropical climates.  The popular image of paleo-indians as meat-eaters is partially true, but an healthy human diet includes carbohydrates.  Surely, paleo-indians were aware that many plants were poisonous, yet the craving for carbohydrates drove them to take chances with unfamiliar roots, tubers, and fruits.  This trial and error likely led to many deaths or at the very least bad stomach aches.  But poisonous compounds are usually bitter.  This important clue helped guide the selection and processing of the unfamiliar plants.  Early people learned that some poisonous plants could be made edible by leaching the poisons in boiling water or by some other processing method.  They must have been really hungry for carbohydrates to make that much effort.  Paleo-indians got lucky when they discovered the wild ancestor of the sweet potato.  There is a species of morning glory (I. pondurata) with an edible root that ranges in southeastern North America.  Reportedly, cooks can rid the bitterness by boiling the root in several changes of water.  It’s likely the first sweet potatoes (a species of morning glory) had to be processed in the same way.  Paleo-Indians were rewarded with an extremely nutritious food.  Sweet potatoes are high in protein, carbohydrate, magnesium, potassium, sodium, phosphorus, vitamin C, B vitamins, and beta-carotene which the human body converts to vitamin A.

Thousands of years of deliberate cultivation has led to many delicious varieties of sweet potatoes that need no processing other than baking.  There are orange, yellow, white, and purple sweet potatoes.

Different varieties of sweet potatoes.

Scientists think the sweet potato is the result of a cross between this species of morning glory and another unknown ancestral species in the ipomoea genus.  Humans crossed them either accidentally or deliberately.

Ipomoea pandurata is a morning glory with an edible root that is native to southeastern North America.  The roots reportedly need quite a bit of processing to make them palatable. The seeds of I. violacca are used as an hallucinogen similar to LSD.

I like candied sweet potatoes with or without marshmallows, but I think the best way to prepare them is by simply baking them, then serving with plenty of butter and cinnamon sugar.  I use baked sweet potato flesh in pies I make with condensed sweetened milk, brown sugar, eggs, ginger, and nutmeg.  White sweet potatoes are drier but sweeter than orange sweet potatoes.  Yellow sweet potatoes were the most popular variety in the U.S. during the 1930’s but have since fallen from favor and are hard to find, yet they taste as good as the orange ones.

Sweet potatoes grown in Louisiana and Mississippi are marketed as “yams” but they are not true yams–a root rarely found in the supermarket.  True yams are not closely related to sweet potatoes but belong to the dioscorea genus.

Canna flaccida

Canna flaccida. The roots of the canna lily have also been eaten in Peru for thousands of years, probably since the Pleistocene.

Ollucos

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The remains of olluco (Ullucus tuberosus), another edible species  found in the Chilca Canyon caverns, date to possibly 10,000 BP.

References:

Ugent, Donald; and Lande Peterson

“Archaeological Remains of Potato and Sweet Potato in Perus”

International Potato Center 1988

Zhang, D.P.; et. al.

“AFCP Assessment of Sweet Potato Genetic Diversity in 4 Tropical American Regions”

International Potato Center 1997-1998

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