Despite the modest amount of starch grains found in the dental calculus samples, the results revealed direct evidence that early modern human ate acorns, roots, tubers, grass seeds, and other yet-unidentified plants as food in marine isotope stage 5 (MIS5) approximately 100 ka. Forty percent of the starch grains analyzed were from acorns. These findings show that acorns were potentially an abundant food resource. Acorns generally refer to the nuts of Quercus, Lithocarpus, Castanopsis, Cyclobalanopsis, and other plants of Fagaceae. Acorns today are widely distributed in China 30,31, including around Fuyan Cave. Exploitation of acorns as a carbohydrate source is well documented in prehistoric and recent times. Starch grains on grinding stones and pottery from numerous sites in China have been reported from the Upper Paleolithic to the Middle Neolithic 17,23,30,36.
Our study provides the earliest evidence that acorns may have played an important role in human subsistence strategies approximately 80 ka in late Paleolithic China. We also provide evidence that these plants have been exploited for a long time, and that humans started using this food resource earlier than previously estimated. Some species of acorns, such as Castanopsis and Cyclobalanopsis, constitute a particularly valuable nutritional source. These plants probably increased intake of vegetable fat and would likely have facilitated early modern humans’ access to food energy. Modern humans also require a reliable source of glycemic carbohydrates to support the normal functioning of the brain, kidney medulla, red blood cells, and reproductive tissues 37. Under normal circumstances, a glucose requirement of approximately 170 g/day is met by a mixture of dietary carbohydrates 38. Roots and tubers are high in carbohydrates 11. Therefore, roots and tubers, as important food sources, are an important factor in early human body evolution. However, roots and tubers are perishable and difficult to preserve, and it is difficult to obtain their macro remains. In contrast, starch grains extracted from dental calculus are good direct evidence of root and tuber consumption 18,21. Starch granules of roots and tubers have been reported from numerous sites dating from the Paleolithic to the Neolithic 28,29,39,40.
Dioscorea starches have been found from grinding stones at the Shizitan site, which dates back to 28–18 ka 15,16. Our evidence indicates that humans in South China ate carbohydrates from roots and tubers, at least 80 ka. In particular, our findings greatly advance our understanding of the history of roots and tubers.
Triticeae plant remains were first found at the Shizitan site as far back as 28 ka16. Two Triticeae starch grains were also recovered from the dental calculus of human teeth from Fuyan Cave in Hunan, South China; although only two grains were recovered, this indicated that the use of Triticeae plants began at least 80 ka. In addition to Triticeae, possible seeds of other grasses were also found.
Our results showed that the earliest direct evidence for human use of these wild grass seeds for food in the MIS5 period was approximately 80 ka, which indicates a long-lasting tradition of using Triticeae plants for subsistence during the Late Pleistocene in China. These findings also suggest a very long history of Triticeae exploitation as part of broad-spectrum subsistence strategies prior to its domestication.
Humphrey et al. (2014) 41showed that high intake of starch plants (such as acorns) can lead to a certain degree of dental caries because frequent consumption of carbohydrates is a key factor in the initiation and progression of this disease. One early modern human in Daoxian had obvious dental caries (Fig2c) and starch grains from acorns such as Castanopsis spp. were also found in this individual's dental calculus (No.DX7). This occurrence of dental caries may have been related to the carbohydrates found in acorns.
Acorns have tannin and need to be processed before human consumption 15,42. It is worth mentioning that some starch grains displayed damage possibly caused by food processing. Food processing technology seems to have developed much earlier than previously detected, and early modern humans in Daoxian may have had this technology 80 ka.
Coniferous fragments were also found in the dental calculus of two Daoxian human teeth 80 ka. Similar evidence was also found in the remains of pottery from the Kuahuqiao site (more than 8 ka) in China 27 and in the dental calculus of a Neanderthal population from a 49,000-year-old site in Spain 35. In addition to coniferous calculus (Fig4a-c) extracted from Daoxian teeth (No.DX4), a groove with numerous fine and parallel scratches was also found from the same tooth of its crown (Fig4d-g). The coniferous fragments (Fig4b, c) and parallel micro scratches in the groove (Fig4d-g) indicate that Daoxian humans habitually rubbed material between their teeth, similar to Neanderthals. Comparison of plant foods in the diets of Neanderthals and early modern humans from several populations in Europe, the Near East, Africa, and East Asia revealed that early modern humans similarly consumed a wide array of plant foods worldwide14. Early modern humans ate more plant foods, and some analyzed starch grains show evidence of cooking damage. The survival and adaptability of Neanderthals may not have been as successful as those of early modern humans. Neanderthals primarily consumed plant foods that required little processing. Our results further indicate that a broader dietary spectrum already existed in early modern humans by the MIS5 period in East Asia.
Our results support that consumption of increased amounts of starch may have provided a substantial evolutionary advantage for early modern humans in the late Middle and early Upper Pleistocene in East Asia because of the energy it supplied to their increasingly large brain and other glucose-dependent tissues.