Modern humans were cooking carbohydrate-rich food as early as 1,70,000 years ago, according to a study which has found the first evidence of this kind from charred remains of plant parts found during excavations in South Africa.
The researchers, including those from the University of the Witwatersrand (Wits) in South Africa, said edible root parts from the plant Hypoxis sp. -- a genus of small flowering plants -- may have been a reliable and transportable staple food for Middle Stone Age humans who lived between 2,80,000-25,000 years ago.
According to the scientists, the starchy root may have also been a familiar source of food for early human populations travelling throughout Africa and beyond.
"This discovery is much older than earlier reports for cooking similar plants and it provides a fascinating insight into the behavioural practices of early modern humans in southern Africa. It also implies that they shared food and used wooden sticks to extract plants from the ground," said study co-author Lyn Wadley from Wits.
While researchers have been able to re-imagine early human hunting strategies, and animal-based diets based on clues from bones and stone tools they left behind, their plant-based diets have often been difficult to determine due to their perishable nature as evidence in archeological sites.
"It is extraordinary that such fragile plant remains have survived for so long," Christine Sievers, study co-author at Wits, said.
The scientists recognised the small, charred cylinders as the root parts, rhizomes.
Using a scanning electron microscope, the researchers zoomed in on the food and water transport channels -- xylem and phloem, in the rhizomes, and identified the 55 charred remains as those of Hypoxis, commonly called the Yellow Star flower.
"The most likely of the species growing in KwaZulu-Natal today is the slender-leafed Hypoxis angustifolia that is favoured as food. It has small rhizomes with white flesh that is more palatable than the bitter, orange flesh of rhizomes from the better known medicinal Hypoxis species (incorrectly called African Potato)," Sievers said.
According to the study, the rhizome is nutritious and carbohydrate-rich, with an energy value of approximately 500 kilojoules per 100 grams.
In comparison, boiled potatoes have approximately 345 kilojoules per 100 grams, and the same weight of baked ones pack 365 kilojoules.
While the Hypoxis rhizomes are edible raw, the scientists said they are fibrous and have high fracture toughness until they are cooked.
They added that the rhizomes are rich in starch, and may have been an ideal staple plant food.
"Cooking the fibre-rich rhizomes would have made them easier to peel and to digest so more of them could be consumed and the nutritional benefits would be greater," said Wadley.
Based on the findings, the scientists said the early modern humans may have used wooden digging sticks to extract the rhizomes from the ground.
"One of these tools was found at Border Cave and is directly dated at circa 40,000 years ago," said Francesco d'Errico, another co-author of the study.
The plant samples were mostly recovered from fireplaces and ash dumps.
"The Border Cave inhabitants would have dug Hypoxis rhizomes from the hillside near the cave, and carried them back to the cave to cook them in the ashes of fireplaces," Wadley added.
According to the scientists, the stone-age humans may have shared the starchy food with each other at the home base since there's evidence that the rhizomes were brought back to the cave rather than cooked in the field.
"This suggests that the rhizomes were roasted in ashes and that, in the process, some were lost. While the evidence for cooking is circumstantial, it is nonetheless compelling," Wadley explained.
"All of the rhizome's attributes imply that it could have provided a reliable, familiar food source for early humans trekking within Africa, or even out of Africa," She said.
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