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Analysis of Early Iron Age (2500 BP) and modern period (150 BP) starch grains in Western Central Africa

PMCID: PMC9643481

PMID: 36347970

Abstract

Starch grain analysis carried out on 23 ceramic sherds from 6 refuse pits from the site of Nachtigal in central Cameroon is shedding light on a longstanding debate regarding ancient diets in Central Africa during the Iron Age (IA, 2500 years BP) but also more recently during the Modern Period (ca. 150 BP). The results indicate a varied, but balanced diet, consisting of cereals, legumes, oil-rich seeds, and tubers; the latter being very rarely documented in the region. Moreover, we underscore the presence of taxa still consumed today, or in recent times. Rescue archaeology, and the application of specialized methodologies, are critical to better nuancing past dietary practices in this region.

Full Text

In this article we present the preliminary results from starch grains recovered from ceramics dated to the EIA (ca. 2500–2200 BP) and the modern period (ca. 150 BP) recovered from refuse pits located north of the modern city of Yaoundé (Cameroon, Fig. 1) and discovered on a dam construction site. Starch grains are microscopic (1–100 μm), composed of two glucose polymers (amylose and amylopectin) and are stored in plant organs, notably in seeds, fruits, and underground storage organs, a term that includes roots, rhizomes, and tubers. A number of features, such as their size, shape, and presence or absence of lamellae, hila, and fissures, allows us in many cases to identify the starch grain to a particular taxon. As not all plants and plant parts are processed in the same way, nor will they preserve in the same manner in the archaeological record, starch grain analysis allows us to further address the numerous questions scholars still have regarding plant diets in CWA. Our preliminary study does not propose to answer all these questions related to diets but does contribute new data on the plant resources likely consumed by the local populations and seeks to highlight the potential of applying microbotanical analysis to material recovered during rescue archaeology, which has significantly developed in the region in the last two decades.
The rescue archaeology program on the Nachtigal Amont hydroelectric dam site conducted by a Franco-Cameroonian IRD (Institut de Recherche pour le Développement) team (February 2019-July 2021) has to date documented more than 161 archaeological sites across more than 721 hectares. The most numerous sites date to the Early Iron Age (EIA) and the Modern period. A preliminary study which sought to recover starch grains was carried out on sherds recovered from 6 refuse pits, from which charcoal and Canarium kernels were radiocarbon dated (Table 1). Four pits contained ceramics similar to those of the Yaoundé region that date to the EIA, while the other two had ceramics decorated using wooden carved roulettes that date to the modern period.
A total of 23 sherds were studied from 18 different vessels (16 from the EIA). For the modern period, the selected sherds are probably from necked jars decorated with engraved roulette wheels of medium-sized vessels (opening diameter probably between 10 and 15 cm: Fig. 2A,B). For the EIA period, the analyzed ceramics, of medium size (opening diameter between 10 and 18 cm), are mostly decorated and consist of ovoid jars with necks, and bowls (Fig. 2C,D). A fragment of a cylindrical spout (from a jar or bowl) was also analyzed (Fig. 2E). The pottery sherds all come from refuse pits which can be assumed to have been filled within the span of a few decades at most, due to the frequent refitting of sherds from very different depths. Thus, we assume that the radiocarbon dates are globally attributable to the analyzed artefacts, even if the depths are not always exactly the same.
This study permitted to recover a total of 381 starch grains (not including the clusters; Table 2). For the EIA, 363 starch grains were recovered, while 18 for the modern period.
Type A: In parentheses, the number of starch grains that are closer in shape and size to sorghum (see also Figures S1, S2, and S3).
The taxa preliminarily identified include lenticular grains, which have been observed in okra seeds (Abelmoschus esculentus, Fig. 3A,B). We also recovered members of the Fabaceae family such as the Bambara groundnut (Vigna subterranea) and cowpea (V. unguiculata, Fig. 3C,D), as well as white-seed melon (Cucumeropsis sp., Fig. 3E,F), raffia palm (Raphia sp., Fig. 3G,H), Gabon nut (Coula edulis, Fig. 3I,J), and members of the Poaceae family. Given the difficulties in differentiating between starch grains of sorghum and pearl millet, we included these in a separate category (Type A, Fig. 3K,L) whenever there was any doubt on their botanical origin. Based on the larger size of a selection of these grains however (Supplementary Figures S1–3), we tentatively identified 31 sorghum starch grains for the EIA, and 1 for the modern period (Fig. 3M,N). These latter starch grains have a mean maximum length of 23.7 μm, are polygonal and have a centric hilum that present a crease, comparably to Bleasdale and colleagues who identified similar starch grains in one Late Iron Age sample from Central Africa.
Clearly ubiquitous in the EIA ceramics are Types B and C, which remain unidentified: the former is ovalish with a central fissure and measuring between 17 and 20 μm, while the latter are strongly facetted grains that measure on average 20 μm in width. Type D starch grains can be divided into two size categories: small (14–20 μm, Fig. 3O,P), and large (60–90 μm, Fig. 3Q,R). Although the larger ones are all highly damaged, both the large and smaller starch grains are good candidates for yams (Dioscorea spp.).
Several types of damages were observed in the samples. The first can be seen on individual starch grains, such as the loss of birefringence (the ability to doubly refract polarized light) and changes in their morphology (Fig. 4). These damages are likely due to exposure to heat in the presence of moisture, so potentially from boiling. Two of these starch grains potentially belong to a tuber (i.e., Dioscorea sp.) given their size, visibility of the lamellae (in the case of Fig. 4A), and the eccentric hilum in Fig. 4F. Moreover, other damages seen on some of the starch grains may be explained by mechanical grinding. These damages include starch grains that look burst (Fig. 4G,H), as well as crushed grains with fissures and fractures along the edges, and damage to the extinction cross (Fig. 4I–L).
Moreover, there were gelatinized masses, composed of starch grains that have undergone irreversible structural and morphological changes, making it difficult at times to further identify them. In some cases, however, the taxon can still be identified, such as in the case of a small cluster where the starch grains resemble those of okra (Fig. 5A,B). In other cases, the masses are too damaged and little more can be said, except that these are likely the result of cooking (i.e., high temperatures) and were found in several samples (Fig. 5C,H).
Other plant remains were present (e.g., sclereids, phytoliths, vascular tissue, trichomes, Fig. 6), and while these could not all be identified further, they likely highlight the use of these ceramics to hold and prepare a range of vegetal-based preparations. Phytoliths were also recovered but not studied further. Other microfossils include opaque perforated platelets belonging to inflorescences in the Asteraceae family (Fig. 6A), as well as different types of sclereids, which are specialized cells found in seed coats, leaves, and also fruits (e.g., Fig. 6C). The leaf epidermis (Fig. 6F) belongs to a monocotyledon, given the dumbbell shape of the guard cells surrounding the stomata. Algae and sponge spicules were also recovered, but no further identification was made (Fig. 6G, H). The presence of microfossil charcoal fragments was noticed in some of the samples (seen for example in Fig. 6E, G) but were again, not considered further in this article.
The archaeological starch grains were compared to those in our reference collection obtained from a range of plant organs from taxa native to West and Central Africa (Supplementary Fig. S4). The present study complies with relevant institutional, national, and international guidelines and legislation. The plants are for the most part sourced from the plant collection of the ArScAn archaeobotany laboratory at the MSH Mondes in Nanterre (France) and the UMR 7209 AASPE (National Museum of Natural History) laboratory in Paris. To complete the collection, seeds from cultivated plants used in the food industry were purchased in France.

Sections

"[{\"pmc\": \"PMC9643481\", \"pmid\": \"36347970\", \"reference_ids\": [\"Fig1\"], \"section\": \"Introduction\", \"text\": \"In this article we present the preliminary results from starch grains recovered from ceramics dated to the EIA (ca. 2500\\u20132200 BP) and the modern period (ca. 150 BP) recovered from refuse pits located north of the modern city of Yaound\\u00e9 (Cameroon, Fig.\\u00a01) and discovered on a dam construction site. Starch grains are microscopic (1\\u2013100\\u00a0\\u03bcm), composed of two glucose polymers (amylose and amylopectin) and are stored in plant organs, notably in seeds, fruits, and underground storage organs, a term that includes roots, rhizomes, and tubers. A number of features, such as their size, shape, and presence or absence of lamellae, hila, and fissures, allows us in many cases to identify the starch grain to a particular taxon. As not all plants and plant parts are processed in the same way, nor will they preserve\\u00a0in the same manner in the archaeological record, starch grain analysis allows us to further address the numerous questions scholars still have regarding plant diets in CWA. Our preliminary study does not propose to answer all these questions related to diets but does contribute new data on the plant resources likely consumed by the local populations and seeks to highlight the potential of applying microbotanical analysis to material recovered during rescue archaeology, which has significantly developed in the region in the last two decades.\"}, {\"pmc\": \"PMC9643481\", \"pmid\": \"36347970\", \"reference_ids\": [\"Tab1\"], \"section\": \"Location and context\", \"text\": \"The rescue archaeology program on the Nachtigal Amont hydroelectric dam site conducted by a Franco-Cameroonian IRD (Institut de Recherche pour le D\\u00e9veloppement) team (February 2019-July 2021) has to date documented more than 161 archaeological sites across more than 721 hectares. The most numerous sites date to the Early Iron Age (EIA) and the Modern period. A preliminary study which sought to recover starch grains was carried out on sherds recovered from 6 refuse pits, from which charcoal and Canarium kernels were radiocarbon dated (Table 1). Four pits contained ceramics similar to those of the Yaound\\u00e9 region that date to the EIA, while the other two had ceramics decorated using wooden carved roulettes that date to the modern period.\"}, {\"pmc\": \"PMC9643481\", \"pmid\": \"36347970\", \"reference_ids\": [\"Fig2\", \"Fig2\", \"Fig2\"], \"section\": \"Location and context\", \"text\": \"A total of 23 sherds were studied from 18 different vessels (16 from the EIA). For the modern period, the selected sherds are probably from necked jars decorated with engraved roulette wheels of medium-sized vessels (opening diameter probably between 10 and 15\\u00a0cm: Fig.\\u00a02A,B). For the EIA period, the analyzed ceramics, of medium size (opening diameter\\u00a0between 10 and 18\\u00a0cm), are mostly decorated and consist of ovoid jars with necks, and bowls (Fig.\\u00a02C,D). A fragment of a cylindrical spout (from a jar or bowl) was also analyzed (Fig.\\u00a02E). The pottery sherds all come from refuse pits which can be assumed to have been filled within the span of a few decades at most, due to the frequent refitting of sherds from very different depths. Thus, we assume that the radiocarbon dates are globally attributable to the analyzed artefacts, even if the depths are not always exactly the same.\"}, {\"pmc\": \"PMC9643481\", \"pmid\": \"36347970\", \"reference_ids\": [\"Tab2\"], \"section\": \"Results\", \"text\": \"This study permitted to recover a total of 381 starch grains (not including the clusters; Table 2). For the EIA, 363 starch grains were recovered, while 18 for the modern period.\"}, {\"pmc\": \"PMC9643481\", \"pmid\": \"36347970\", \"reference_ids\": [\"MOESM1\", \"MOESM1\", \"MOESM1\"], \"section\": \"\", \"text\": \"Type A: In parentheses, the number of starch grains that are closer in shape and size to sorghum (see also Figures S1, S2, and S3).\"}, {\"pmc\": \"PMC9643481\", \"pmid\": \"36347970\", \"reference_ids\": [\"Fig3\", \"Fig3\", \"Fig3\", \"Fig3\", \"Fig3\", \"Fig3\", \"MOESM1\", \"Fig3\"], \"section\": \"Results\", \"text\": \"The taxa preliminarily identified include lenticular grains, which have been observed in okra seeds (Abelmoschus esculentus, Fig.\\u00a03A,B). We also recovered members of the Fabaceae family such as the Bambara groundnut (Vigna subterranea) and cowpea (V. unguiculata, Fig.\\u00a03C,D), as well as white-seed melon (Cucumeropsis sp., Fig.\\u00a03E,F), raffia palm (Raphia sp., Fig.\\u00a03G,H), Gabon nut (Coula edulis, Fig.\\u00a03I,J), and members of the Poaceae family. Given the difficulties in differentiating between starch grains of sorghum and pearl millet, we included these in a separate category (Type A, Fig.\\u00a03K,L) whenever there was any doubt on their botanical origin. Based on the larger size of a selection of these grains however (Supplementary Figures S1\\u20133), we tentatively identified 31 sorghum starch grains for the EIA, and 1 for the modern period (Fig.\\u00a03M,N). These latter starch grains have a mean maximum length of 23.7\\u00a0\\u03bcm, are polygonal and have a centric hilum that present a crease, comparably to Bleasdale and colleagues who identified similar starch grains in one Late Iron Age sample from Central Africa.\"}, {\"pmc\": \"PMC9643481\", \"pmid\": \"36347970\", \"reference_ids\": [\"Fig3\", \"Fig3\"], \"section\": \"Results\", \"text\": \"Clearly ubiquitous in the EIA ceramics are Types B and C, which remain unidentified: the former is ovalish with a central fissure and measuring between 17 and 20\\u00a0\\u03bcm, while the latter are strongly facetted grains that measure on average 20\\u00a0\\u03bcm in width. Type D starch grains can be divided into two size categories: small (14\\u201320\\u00a0\\u03bcm, Fig.\\u00a03O,P), and large (60\\u201390\\u00a0\\u03bcm, Fig.\\u00a03Q,R). Although the larger ones are all highly damaged, both the large and smaller starch grains are good candidates for yams (Dioscorea spp.).\"}, {\"pmc\": \"PMC9643481\", \"pmid\": \"36347970\", \"reference_ids\": [\"Fig4\", \"Fig4\", \"Fig4\", \"Fig4\", \"Fig4\"], \"section\": \"Results\", \"text\": \"Several types of damages were observed in the samples. The first can be seen on individual starch grains, such as the loss of birefringence (the ability to doubly refract polarized light) and changes in their morphology (Fig.\\u00a04). These damages are likely due to exposure to heat in the presence of moisture, so potentially from boiling. Two of these starch grains potentially belong to a tuber (i.e., Dioscorea sp.) given their size, visibility of the lamellae (in the case of Fig.\\u00a04A), and the eccentric hilum in Fig.\\u00a04F. Moreover, other damages seen on some of the starch grains may be explained by mechanical grinding. These damages include starch grains that look burst (Fig.\\u00a04G,H), as well as crushed grains with fissures and fractures along the edges, and damage to the extinction cross (Fig.\\u00a04I\\u2013L).\"}, {\"pmc\": \"PMC9643481\", \"pmid\": \"36347970\", \"reference_ids\": [\"Fig5\", \"Fig5\"], \"section\": \"Results\", \"text\": \"Moreover, there were gelatinized masses, composed of starch grains that have undergone irreversible structural and morphological changes, making it difficult at times to further identify\\u00a0them. In some cases, however, the taxon can still be identified, such as in the case of a small cluster where the starch grains resemble those of okra (Fig.\\u00a05A,B). In other cases, the masses are too damaged and little more can be said, except that these are likely the result of cooking (i.e., high temperatures) and were found in several samples (Fig.\\u00a05C,H).\"}, {\"pmc\": \"PMC9643481\", \"pmid\": \"36347970\", \"reference_ids\": [\"Fig6\", \"Fig6\", \"Fig6\", \"Fig6\", \"Fig6\", \"Fig6\"], \"section\": \"Results\", \"text\": \"Other plant remains were present (e.g., sclereids, phytoliths, vascular tissue, trichomes, Fig.\\u00a06), and while these could not all be identified further, they likely highlight the use of these ceramics to hold and prepare a range of vegetal-based preparations. Phytoliths were also recovered but not studied further. Other microfossils include opaque perforated platelets belonging to inflorescences in the Asteraceae family (Fig.\\u00a06A), as well as different types of sclereids, which are specialized cells found in seed coats, leaves, and also fruits (e.g., Fig.\\u00a06C). The leaf epidermis (Fig.\\u00a06F) belongs to a monocotyledon, given the dumbbell shape of the guard cells surrounding the stomata. Algae and sponge spicules were also recovered, but no further identification was made (Fig.\\u00a06G, H). The presence of microfossil charcoal fragments was noticed in some of the samples (seen for example in Fig.\\u00a06E, G) but were again, not considered further in this article.\"}, {\"pmc\": \"PMC9643481\", \"pmid\": \"36347970\", \"reference_ids\": [\"MOESM1\"], \"section\": \"Methods\", \"text\": \"The archaeological starch grains were compared to those in our reference collection obtained from a range of plant organs from\\u00a0taxa native to West and Central Africa (Supplementary Fig. S4). The present study complies with relevant institutional, national, and international guidelines and legislation. The plants are for the most part sourced from the plant collection of the ArScAn archaeobotany laboratory at the MSH Mondes in Nanterre (France) and the\\u00a0UMR 7209 AASPE (National Museum of Natural History) laboratory in Paris. To complete the collection, seeds from cultivated plants used in the food industry were purchased in France.\"}]"

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