To start with our discussion of the findings we need to consider some limitations of the method. The pathways of inclusion of starch granules of different species in the dental calculus matrix are different and a specific “rate” has never been calculated. Theoretically, this property depends on biological individual factors (saliva, dental anatomy, microflora) and several physical attributes of food related to cooking methods (texture, if raw or gelatinized), sugar and fiber content of the species, etc. and needs more experimental work to be elucidated28. Thus, the presence of starch of edible plants trapped in dental calculus only provides confirmation that some specific species were introduced in the mouth, chewed, and possibly ingested, we cannot know if they represent more or less consumption in absolute quantitative terms. To unravel this, are necessary other sources of evidence.
Various plants identified in the human dental calculus are consistent with the macrobotanical evidence reported in Áspero and Sacred City of Caral sites4,5,6,20. Nonetheless, there are some taxa identified in this study that were not reported in the macrobotanical record. For example, manioc remains were not recovered and sweet potato and potato macroremains are relatively scarce in Supe Valley4,5,6,20. The absence or low number of recovered tubers among the macroremains can be associated with poor preservation and/or total consumption. On the other hand, guava starches were not reported in our analysis, however, remains of seeds of this fruit are very abundant in the macrobotanical record from Áspero and Sacred City of Caral 4,5,6,20. This discrepancy probably could be explained by issues of starch preservation in the matrix of the dental calculus, a topic still poorly explored. These results highlight the importance of performing several complementary analyses.
In contrast to the macrobotanical analysis, our microbotanical analysis retrieved a high number of sweet potato starches from dental calculus in Áspero and Sacred City of Caral. Sweet potato (30.8%) and squash (25.3%) starch grains represent more than a half of the total recovered grains (Table 1), suggesting, with caution, a more frequent consumption of these plants in coastal Supe Valley during the Initial Formative Period. These results agree with the isotopic analyses that suggest that C3 plants formed the basis of the diet at Áspero and Sacred City of Caral 18. The most important contribution of this study is the identification of the specific taxa of C3 plants consumed. Our findings show that the C3 tuber more conspicuous in Áspero was sweet potato, and that squash was also an important C3 source in the menu. Our results also indicate the consumption of achira (Fig. 2o-p) at Aspero, which is one of the most common C3 tubers found in the macrobotanical remains recovered from the excavations at Aspero and Caral. Other C3 tubers identified in this study were potato (Fig. 2q-r) (2.9%) and manioc (Fig. 2m-n) (0.4%). The low occurrence of potato and manioc starch throughout the Initial Formative Period in the Supe Valley could be interpreted as a more occasional consumption of these tubers, although preservation issues could be also related. Potato and manioc are believed to have been domesticated in southern-central Andes and southern Amazon, respectively29,30,31. Despite their original center of domestication, potato and manioc, as today, can grow in middle coastal valleys. However, it is also plausible that inhabitants of Supe Valley, especially those from Áspero, acquired potato and manioc through exchange from other regions of higher altitude.
Other common C3 species of Initial Formative Period identified in this study, also reported in macrobotanical analyses in Áspero and Sacred City of Caral 4,5,6,20, are chili peppers (Fig. 2u-v) and legumes (Fig. 2s-t and Fig. 2w-x). However, both species presented a low number of starches in human dental calculus. In contrast, a previous study of plant micro-remains trapped into dental calculus indicates that legumes and squashes were the major dietary sources in northern Peru (Nanchoc Valley, 6210 − 4970 BCE)23. During the Initial Formative Period, at least in the coastal of Supe Valley, a more varied starchy food diet based on tubers and squash is noticed, suggesting a temporal trend of change in starchy food diet over the time. It is possible that changes in the subsistence economy with a growing dependence on crops during the Initial Formative Period (farming intensification), was the cause of the differences in sources of starchy food diet between the inhabitants of the Supe Valley and other earlier archeological sites.
Maize starch grains correspond to 16.4% of the total starches recovered. Remains of maize cobs were recovered in Áspero 80 years ago32. However, the archeological context of these findings is uncertain and was the motif of heated33,34,35. Our results indicate that maize starch grains were recovered from burials dated to early stages of the Initial Formative Period (3000 − 2700 BCE) in Áspero. In Caral, based on macro-botanical evidence, Shady21 suggests that maize was incorporated from 2300 BCE. The few remains of maize cobs recovered in Caral are varied, but when compared to other food plants suggest that was a less important component of the population's diet5,21. In addition, the association of maize with ritual contexts was recurrent in Caral21. The maize starch grains recovered in this study are related to the Middle Expansive and Late Caral periods (2398 − 2038 cal. BCE) (Table 1). Another remarkable finding of this work is the evidence of two maize starch grains with damage by possible fermentation process at Áspero (PEACS 3002) and Sacred City of Caral (CAR 391) (Fig. 2k, 2l). The PEACS 3002 individual is temporally located at the end of the Initial Formative Period, while the CAR 391 burial was directly dated 2398 − 2038 cal. BCE and both individuals were recovered from sacrificial contexts20,36. These starches presented radial striations and an irregular extinction cross, similar to starch grains with evidence of fermentation damage reported during the Inca period37. This finding has several important implications. Traditionally, fermentation of maize is related to chicha (maize beer) production and chicha was a widely consumed beverage associated with feasting, rituals and used as a mean to construct and affirm political power by the elites in later periods38,39,40. Their use in ceremonial contexts has been widely demonstrated at least from the Middle Formative41. Due to the logistical limitations of chicha preparation linked to absence of pottery during the Initial Formative Period, the mixing ground maize with saliva to produce fermentation was probably the pathway for the preparation of chicha42 in Áspero and Sacred City of Caral. More robust evidence is needed to confirm that maize was consumed as chicha. Damage of starch linked to fermentation should be evaluated in an expanded sample to test this “working hypothesis”.