The oldest evidence of the cooking of carbohydrate-rich foods has been found at a Middle Stone Age site in South Africa, dated to 170,000 years. The discovery indicates both cooking and high-carb food sources are almost as old as our species, and likely far older. So much for anyone trying to hook you on “paleolithic diets”.

Ancient campsites are littered with the bones of animals hunted by our ancestors, giving us a good idea of the carnivorous component of their diet. Vegetable matter is less evident, but Professor Lyn Wadley of the University of Witwatersrand argues it is also much less likely to be preserved. Diets were certainly far more diverse prior to the development of agriculture than we can see from the ashes of long-gone campfires, making any attempt to assess paleolithic nutrition unreliable.

Now and then, however, unusual conditions provide exceptional preservation, and one such case is at Border Cave, South Africa, where Wadley and colleagues discovered the charred remains of rhizomes, underground plant stems from which roots grow.

The cave floor is made up of alternating layers of sediment and ash from periods of human occupation. Rhizomes were found at many levels, with the earliest dated to around 170,000 years ago, indicating this was a staple food in the area over an immense period of time. Placement in the ash layers indicates they were deliberately roasted in the fires, with a few left behind either from overcooking or being accidentally missed. The cooking also explains why they survived so long.

The rhizomes are from the genus Hypoxis, known as star lilies or African potatoes, and although they were too burnt to be identified definitively, Wadley and co-authors propose in Science that their size and shape are indicative of H. angustifolia. Star lilies exist across most of Africa and are rich in calories, vitamins, and essential minerals. Its rhizomes are edible raw, but cooking softens them. H. angustifolia and its close relatives probably provided a reliable source of food for humans as they expanded their range within Africa and possibly beyond.

Rhizome seeds have been found at a campsite at Gesher Benot Ya'aqov, Israel, that far predate modern humans, but this is less than conclusive evidence for them being eaten, let alone cooked. Border Cave is far older than any evidence of rhizome consumption of similar power. It beats the previous oldest trace of deliberately cooked plant matter by 50,000 years.

We don't know whether these rhizomes were the main meal or a side dish for meat, but one study has found that someone who knows what to look for can gather enough starchy root vegetables in two hours in wild parts of South Africa to feed themselves for a day.