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Edited by Melinda Zeder, National Museum of Natural History, Santa Fe, NM, and approved February 21, 2020 (received for review November 18, 2019)
Significance
Lipid residue analysis of archaeological ceramics provides the earliest direct chemical evidence for milk, meat, and plant consumption by pastoralist societies in eastern Africa. Data for milk in specialized pastoral systems (c. 5000 to 1200 BP) reveal changing selective pressures for lactase persistence and provide support for models of gene–culture coevolution among pastoral populations.
Abstract
The development of pastoralism transformed human diets and societies in grasslands worldwide. The long-term success of cattle herding in Africa has been sustained by dynamic food systems, consumption of a broad range of primary and secondary livestock products, and the evolution of lactase persistence (LP), which allows digestion of lactose into adulthood and enables the milk-based, high-protein, low-calorie diets characteristic of contemporary pastoralists. Despite the presence of multiple alleles associated with LP in ancient and present-day eastern African populations, the contexts for selection for LP and the long-term development of pastoralist foodways in this region remain unclear. Pastoral Neolithic (c. 5000 to 1200 BP) faunas indicate that herders relied on cattle, sheep, and goats and some hunting, but direct information on milk consumption, plant use, and broader culinary patterns is rare. Combined chemical and isotopic analysis of ceramic sherds (n = 125) from Pastoral Neolithic archaeological contexts in Kenya and Tanzania, using compound-specific δ13C and Δ13C values of the major fatty acids, provides chemical evidence for milk, meat, and plant processing by ancient herding societies in eastern Africa. These data provide the earliest direct evidence for milk product consumption and reveal a history of reliance on animal products and other nutrients, likely extracted through soups or stews, and plant foods. They document a 5,000-y temporal framework for eastern Africa pastoralist cuisines and cultural contexts for selection for alleles distinctive of LP in eastern Africa.
Pastoralism is a dominant form of food production in grassland ecosystems globally (1), and genetic histories of pastoralist populations reflect complex interplays among human migrations, interactions, and culinary practices (2). In eastern Africa, mobile herding communities in marginal dryland environments have historically relied on milk-based, high-protein, low-calorie diets (3), facilitated by multiple genetic alleles for lactase persistence (LP) and digestion of milk into adulthood. Although the earliest evidence for cattle, sheep, and goats dates to the Pastoral Neolithic (PN; c. 5000 to 1200 BP), when herders spread into eastern Africa, little is known about the emergence of milk as a food, settings for selection for eastern African alleles for LP, or the long-term development of highly specialized pastoralist foodways. Direct evidence for the consumption of milk, for example, is absent in PN and later archaeological records.
The genetic basis for LP facilitates the ability to survive on livestock milk, as regulatory mutations that affect production of the enzyme lactase and its postweaning retention enable digestion of milk sugars (lactose). It has long been hypothesized that LP is selected for in pastoral populations through gene–culture coevolution, but the roles of cuisine, gut microbiomes, and population interactions are poorly understood, given highly variable selection contexts worldwide (e.g., ref. 4). In southwestern Asia, archaeological data suggest early dairying was based on sheep/goat pastoralism; however, faunal remains and organic residue evidence from pottery from the 9th millennium in NW Anatolia indicate intensification of milk use centered on cattle (5). African herding systems, beginning ∼8000 BP in what is now the Sahara, were characterized by greater mobility, later limited cultivation, and dietary foci on cattle. In eastern Africa today, milk and milk products from cattle (or camels in more arid regions), sheep, and goats provide as much as 60% to 90% of total calories (6⇓–8). Milk shortages during droughts or dry seasons increase vulnerabilities to malnutrition (9⇓–11) and result in increased consumption of meat and within-bone nutrients. Milk and meat are also complemented by seasonally available wild plant foods and, today, introduced staples (e.g., maize and beans). Tishkoff and colleagues (12, 13) suggest that strong selection resulted in the appearance of the C-14010 genetic variant for the LP trait in eastern African populations an estimated ∼6,800 to 2,700 y ago. Evidence for early milk consumption is lacking, but discovery of an individual buried in northern Tanzania, dating to 2200 to 2150 BP, with the C-14010 allele provides a pastoral context for selection (14). The existence of multiple other genetic variants associated with the LP phenotypic trait in contemporary eastern African populations (12, 13) distinguishes this region from most of Eurasia, where a single allele for LP exists (2). All LP variants are present at relatively low frequencies (<45%) (13) in eastern Africa, and it is likely this was also the case in the past (14). It is frequently argued that in the absence of LP, herder dependence on milk can be facilitated by the preparation of fresh milk into more easily digested fermented milk products (2, 13).
Although it is clear from the human genetic data that the ability for herders to digest milk must have been strongly adaptive in eastern Africa, lack of direct information on when and where milk was drunk, how ancient herders prepared their food, and how herders buffered milk shortages has constrained understanding of prehistoric selective contexts for LP. Integrated archaeological and molecular evidence can provide a deeper understanding of when, where, and why LP emerged in eastern Africa, in addition to shedding light on broader dietary patterns. Here, we report lipid residue analyses of 125 ceramic vessels from PN archaeological contexts in Kenya and Tanzania. These data provide the earliest direct evidence for meat, milk, and plant processing or storage by ancient eastern African herders, and offer a globally relevant perspective on the origins of pastoralist dietary adaptations and the evolution of milk-centered husbandry systems.
Pastoral Neolithic Herders
During the PN, communities herding cattle, sheep, goat, and donkey spread throughout the eastern African Rift Valley and beyond, interacting with indigenous hunter-gatherers. Livestock first appear in the Turkana Basin of northwestern Kenya during a period of aridity and social change c. 5000 to 4500 cal BP (3), when herder-fishers built a series of megalithic pillar sites. Some of these are communal cemeteries in which people deposited highly decorated ceramic vessels (15, 16). After c. 3300 cal BP, there was a florescence of specialized herding economies throughout south-central Kenya and into Tanzania. Herders moved into wetter, topographically diverse, and more productive pastoral grazing lands, where cattle herds can provide milk for human consumption almost year-round (17⇓–19).
The sites and samples chosen for this study are broadly representative of the archaeological diversity of the PN. They include ceremonial and habitation sites, span the Turkana Basin in Kenya to the north-central Tanzanian highlands (Fig. 1), and cover the three major PN material culture traditions (see Table 1 for references). Jarigole (GbJji1, c. 5000 to 4500 cal BP) is a megalithic pillar site on the east side of Lake Turkana, and Dongodien (GaJi4, c. 5000 to 4500 cal BP) is a roughly contemporaneous open-air habitation site on the east side of Lake Turkana. Ngamuriak (GuJf6, c. 2000 cal BP) is a settlement site in the Loita-Mara region of southwestern Kenya. Luxmanda (c. 3000 cal BP) is another large open-air settlement site, located on the Mbulu Plateau in north-central Tanzania. A description of sampling strategies and a list of lipid-yielding sherds with contextual information can be found in SI Appendix, Table S1; sherd photographs are in Fig. 2. Previously published radiocarbon dates for each site, along with newly generated compound-specific radiocarbon dates on extracted lipids (20), are in SI Appendix, Table S2.
Fig. 1.
Density and distribution of excavated Pastoral Neolithic sites in eastern Africa: major sites with known coordinates are marked with black dots. Sites sampled for this study are marked with red triangles. Base map source: Natural Earth.
View this table:
Table 1.
Summary table of archaeological information for sampled sites
Fig. 2.
Examples of sherds from each site containing lipid residues. Sherds A–G are considered Nderit pottery (see ref. 45) from the Turkana Basin; exterior surface is shown on the left, interior surface is shown on the right. Jarigole (A, GBJ001; B, GBJ014; C, GBJ016; D, GBJ018; E, GBJ007): A–D are Classic Nderit basketry-like vessels with unidentified forms; for A and B, note internal scoring, for C, note internal shallow impressions. Sherd E has incised grooves in a geometric pattern, common for shallow bowls. Dongodien (F, GAJ003; G, GAJ012): F is Classic Nderit, G has wide grooves, and three undecorated sherds with lipid residues are not pictured. Luxmanda (H, LUX019; I, LUX025; J, LUX065; K, LUX059): sherds are Narosura pottery, common to Savanna Pastoral Neolithic sites. Forms are open-mouthed bowls or globular vessels with comb-stamping or incising in bands under rims. Ngamuriak (L, NMK006; M, NMK8/9/10): sherds are Elmenteitan pottery, undecorated with forms including straight-sided or globular bowls/pots.
Lipid Residue Results
Recovery Rates and Concentrations.
Lipid analysis and interpretations for PN ceramics were performed using established protocols (e.g., refs. 21 and 22). A total of 125 ceramic sherds were sampled from Jarigole (n = 20), Dongodien (n = 20), Ngamuriak (n = 22), and Luxmanda (n = 63). Lipid recovery rates varied, with rates at the two earlier sites, Jarigole and Dongodien, being lower (25%, n = 5 at each site) than at Luxmanda (38%, n = 24), and especially at Ngamuriak, where lipid recovery was very high (82%, n = 18). Lower lipid recovery rates may be taphonomic, but more likely suggest different patterns of vessel use. The mean lipid concentrations of the Jarigole and Dongodien sherds are 0.7 and 0.08 mg⋅g−1, respectively (Table 1), with maximum lipid concentrations of 1.9 mg⋅g−1 (GAJ003) and 0.2 mg⋅g−1 (GBJ014), whereas the mean lipid concentrations for Luxmanda (1.3 mg⋅g−1) and Ngamuriak (3.6 mg⋅g−1) and the maximum lipid concentrations at these sites are considerably higher (Luxmanda, 11.5 mg⋅g−1, LUX019; Ngamuriak, 29.4 mg⋅g−1, NMK018). Several sherds from both later sites contain high concentrations of lipids (e.g., LUX003, 4.6 mg⋅g−1; LUX019, 11.5 mg⋅g−1; LUX038, 5.9 mg⋅g−1; LUX043, 2.7 mg⋅g−1; LUX052, 2.0 mg⋅g−1; NMK004, 2.3 mg⋅g−1; NMK005, 6.2 mg⋅g−1; NMK006, 13.2 mg⋅g−1; NMK8,9,10, 3.4 mg⋅g−1; and NMK018, 29.4 mg⋅g−1). These vessels were likely subjected to sustained use in the processing of high fat-yielding resources.
Meat and Milk.
Analysis of the total lipid extracts (TLEs; n = 125) from all sites, using gas chromatography (GC) and GC-mass spectrometry (GC-MS), demonstrated that 52 sherds contained sufficient concentrations (>5 µg⋅g−1) of lipids to allow reliable interpretation (23). These extracts comprised lipid profiles that demonstrated that palmitic (C16) and stearic (C18) fatty acids, typical of a degraded animal fat (Fig. 3 B–D), were the most abundant components (e.g., ref. 24). Further analyses by GC-combustion-isotope ratio MS (GC-C-IRMS) characterized the source of these animal products through determination of the δ13C values of the major fatty acids, C16:0 and C18:0 (Fig. 4), which allows differentiation between carcass fats from ruminant and nonruminant animals and between ruminant dairy and carcass fats (21, 24).
Fig. 3.
Partial gas chromatograms of trimethylsilylated lipid extracts of pottery. (A) Lipid distributions in LUX032 are indicative of leafy plant processing and (B–D) showing typical degraded animal fat chromatograms, dominated by C16:0 and C18:0 fatty acids, from Dongodien, Luxmanda, and Ngamuriak, respectively. Circles, n-alkanoic acids (fatty acids, FA); triangles, n-alkanes; IS, internal standard, n-tetratriacontane.
Fig. 4.
Graphs showing the Δ13C (δ13C18:0 – δ13C16:0) values from the potsherds at each of the sampled sites: Jarigole, Dongodien, Luxmanda, and Ngamuriak. The ranges shown here represent the mean ± 1 SD of the Δ13C values for a global database comprising published modern reference animal fats from Africa (25), UK (animals raised on a pure C3 diet) (21), Kazakhstan (46), Switzerland (47), and the Near East (48).
At Jarigole (n = 5), one lipid residue plots within the nonruminant (or, possibly, plant) range, with the remaining four plotting within the ruminant adipose region. Ruminant dairy fats are differentiated from adipose fats when they display Δ13C (δ13C18:0 – δ13C16:0) values of less than −3.1‰ (25). Thus, at Jarigole one residue with a Δ13C value of −3.0 plots at the border between adipose and milk fats. At Dongodien (n = 5), one vessel plots in the ruminant dairy range, with two vessels plotting in the ruminant adipose range and a further two plotting in the nonruminant/plant range. Nonruminant mammals potentially present in the area during the PN include equids (zebra and donkey), suids (warthog and bushpig), and small mammals such as hare and hyrax. At Jarigole and Dongodien, δ13C16:0 values (range, −26.3‰ to −16.8‰) suggest that animals were subsisting on both C3 and C4 plants, as confirmed by other datasets at these sites (ref. 17 and SI Appendix, Fig. S2).
The majority of the lipid-bearing residues at the two later PN sites, Luxmanda (83%, n = 20) and Ngamuriak (94%, n = 17), plot within the ruminant carcass range, confirming the dominant use of ceramic vessels for meat processing. δ13C16:0 values (range, −22.1‰ to −12.0‰) for these sites suggest that animals were subsisting mainly on C4 plants, which aligns with stable carbon isotope data for livestock tooth enamel across southern Kenya and northern Tanzania (refs. 17, 26, and 27 and SI Appendix, Fig. S2). One vessel at Luxmanda, LUX004, with a Δ13C of −5.4‰, plots firmly in the ruminant dairy region, with a further vessel (LUX025, −3.1‰), plotting at the boundary of the range. Similarly, at Ngamuriak, vessel NMK020 plots close to the top of the range (Δ13C of −3.4‰), with vessel NMK8/9/10 plotting close to the boundary between meat and milk products.
Plant Processing.
At Luxmanda, two vessels, LUX032 and LUX057, plot within the nonruminant/plant region with enriched Δ13C values of 2.9‰ and 3.7‰, respectively. Interestingly, both vessels have low lipid concentrations, often indicative of plant processing, and the lipid profile of LUX032 includes a series of odd-over-even n-alkanes (Fig. 3A), dominated by C31, likely originating from C3 or C4 wild grasses or lake-margin plants, such as sedges (28⇓⇓–31). A further vessel, LUX030, is dominated by high concentrations of even-over-odd numbered long-chain fatty acids, maximizing at C26, again strongly indicative either of an origin in leaf or stem epicuticular waxes (28).
Freshwater Resources.
Fatty acid methyl esters (FAMEs) from all lipid residues were analyzed by GC-MS in SIM mode to check for the presence of aquatic biomarkers; namely, ω-(o-alkylphenyl) alkanoic acids, vicinal dihydroxy fatty acids, and isoprenoid fatty acids. These are routinely used to detect both marine and freshwater animal product processing (32⇓–34); however, no freshwater biomarkers were detected here. Despite the prevalence of fish bones at Dongodien (35), freshwater resources such as fish may not have been prepared by boiling in pots and could have been cooked in other ways such as roasting, salting, or smoking.
Discussion
Lipid residue analysis of archaeological ceramics provides the earliest direct chemical evidence for milk, meat, and plant consumption by pastoralist societies in eastern Africa. Our results demonstrate that the earliest herders in the region, at Dongodien, c. 5,000 y ago, predominately processed meat products in their pottery vessels, while processing milk or milk products at low frequencies. The presence of milk at Dongodien provides evidence for an extended chronology for selection for the distinctive eastern African basis for LP (C-14010), and raise questions about whether these herders may have carried an allele for LP (e.g., G-13907) common in Sudan or Ethiopia today (see refs. 12 and 13). Meat, fat, and/or bones from livestock and wild fauna (nonruminants) were the predominant products cooked or served in ceramic pots found at the Dongodien settlement and the Jarigole mortuary site. These food residues are consistent with faunal data from Dongodien; however, it is notable that few remains of nonruminant mammals (hyrax and hare) were identified in the faunal assemblage (35). The organic residue data reveal that at least some highly decorated Nderit ceramics found at both early PN mortuary contexts and habitation sites were used in the storage, preparation, or serving of food. All five vessels with preserved lipids at Jarigole, and three from Dongodien, display low lipid concentrations, suggesting they were only used sporadically for cooking or for serving foodstuffs. At Dongodien, two additional vessels (GAJ003 and GAJ013) yielded high lipid concentrations, indicating their possible use as cooking pots, although no use-wear such as sooting on any Nderit pottery indicates use over fire.
In the wetter southern highlands and richer grasslands, faunal remains show that later herders with different mortuary and ceramic traditions c. 3000 to 2000 BP kept large cattle herds and depended on livestock, with little to no reliance on wild fauna (36, 37). Lipid residues demonstrate that herders at the Luxmanda and Ngamuriak settlement sites used their pottery predominantly for processing ruminant carcass products, and to a lesser extent for processing milk. Comparison with lipid residues extracted from ceramics used by heavily milk-reliant Samburu pastoralists in northern Kenya today revealed a broadly similar pattern (38). In Samburu, this pattern reflects container choices, rather than degree of reliance on milk in the diet (9). Meat and bones are cooked in pots, while milk, for both ceremonial and daily use, is generally collected, stored, and processed in wooden vessels and gourds, which rarely preserve at archaeological sites.
Lipid assemblages at Ngamuriak and Luxmanda are dominated by ruminant carcass product processing, which corresponds well with highly fragmented cattle, sheep, and goat bone assemblages (18, 26). Extremely high lipid concentrations from nearly all Ngamuriak vessels and many of the Luxmanda vessels indicate that ceramic technologies throughout the PN played a critical role in the repeated preparation of meat, bones, marrow, and/or fat, likely through breakage and boiling of bones. Furthermore, lipid profiles at Luxmanda provide evidence for plant processing in the PN. Given otherwise good preservation of lipids at Luxmanda, the large number of sherds with no detectable lipid residues may come from pots that served other functions such as serving or storage of low lipid-yielding foods.
At a larger scale, our findings demonstrate that as herders spread throughout eastern Africa following Saharan expansion, food-producing economies incorporated carcass processing in pots and the use of milk from the earliest PN, and plant processing in pots by the later PN. Lipid residue data are relatively consistent across a wide geographic area, different site types, and different material traditions: Throughout the PN, herders used pots to process predominantly ruminant carcass products and, infrequently, milk or milk-based products. Notwithstanding the low frequency of milk processing, the evidence is robust. Hence, this time frame provides a relatively long period in which selection for the LP trait may have occurred within multiple groups in eastern Africa, which supports genetic estimations. Settings for selection differed with social and economic organization and environment. Diversified reliance on livestock, fishing, and hunting at Lake Turkana 5,000 y ago provided herders in this arid region with alternatives to reliance on milk or slaughtering of livestock during times of seasonal shortage or drought. Conversely, lipid residue and faunal data reveal that pastoralists who lived at Ngamuriak and Luxmanda in the rich grazing lands of southwestern Kenya and northern Tanzania relied almost exclusively on their livestock, and possibly plants. Given pastoralist specialization, selection for LP in east Africa (the C-14010 allele) may have been stronger among specialized pastoral groups after 3100 BP in more southerly regions than earlier at Lake Turkana in the north.
The earliest herders in northern Kenya 5,000 y ago drank milk or ate milk-based products, but ceramic vessels with preserved lipid residues, found at both ceremonial and settlement sites, were predominantly used for processing or serving carcass products from livestock. Later specialized herders in southwest Kenya and north-central Tanzania c. 3000 to 2000 BP intensively processed livestock carcass fats in ceramic vessels, similar to how Samburu herders use ceramics today. These results reveal the changing significance of livestock, and their milk, to herder diets and have broader relevance for understanding the biological histories of herders in eastern Africa. These histories are likely the result of gene-culture coevolution involving complex interplays among migrations, diverse livestock management strategies, local ecologies, and dietary and culinary adaptations spanning thousands of years.
Materials and Methods
Lipid analysis and interpretations were performed using established protocols described in detail in earlier publications (e.g., refs. 21 and 22). All solvents used were HPLC grade (Rathburn), and the reagents were analytical grade (typically >98% of purity). Briefly, ∼2 g of potsherd were sampled and surfaces cleaned with a modeling drill to remove any exogenous lipids. The sherds were ground to a powder and an internal standard, typically 40 μg, was added to enable quantification of the lipid extract (n-tetratriacontane; Sigma Aldrich Company Ltd). Following the addition of 5 mL H2SO4/MeOH 2% to 4% vol/vol (δ13C of MeOH measured), the culture tubes were placed on a heating block for 1 h at 70 °C, mixing every 10 min. Once cooled, the methanolic acid was transferred to test tubes and centrifuged at 2,500 rpm for 10 min. The supernatant was then decanted into another furnace culture tube (II) and 2 mL dichloromethane (DCM) extracted double-distilled water was added. To recover any lipids not fully solubilized by the methanol solution, 2 × 3 mL n-hexane was added to the extracted potsherds contained in the original culture tubes, mixed well, and transferred to culture tube II. The extraction was transferred to a clean, furnaced 3.5-mL vial and blown down to dryness. Following this, 2 × 2 mL n-hexane was added directly to the H2SO4/MeOH solution in culture tube II and whirlimixed to extract the remaining residues. This was transferred to the 3.5-mL vials and blown down until a full vial of solvent remained. Aliquots of the lipid extracts were derivatized using N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) containing 1% vol/vol trimethylchlorosilane (TMCS; Sigma Aldrich Company Ltd.; 20 μL; 70 °C, 1 h). Excess BSTFA was removed under nitrogen, and the derivatized FAME was dissolved in hexane before GC, GC-MS, and GC-C-IRMS.
All FAMEs initially underwent high-temperature GC using a gas chromatograph fitted with a high-temperature nonpolar column (DB1-HT; 100% dimethylpolysiloxane, 15 m × 0.32 mm i.d., 0.1 μm film thickness). The carrier gas was helium and the temperature program comprised a 50 °C isothermal hold followed by an increase to 350 °C at a rate of 10 °C⋅min−1 followed by a 10-min isothermal hold. A procedural blank (no sample) was prepared and analyzed alongside every batch of samples. Further compound identification was accomplished using GC-MS. FAMEs were then introduced by autosampler onto a GC-MS fitted with a nonpolar column (HP-1; 100% dimethyl polysiloxane stationary phase; 60 m × 0.25 mm i.d., 0.1 μm film thickness). The instrument was a ThermoFinnigan single quadrupole TraceMS run in EI mode (electron energy 70 eV, scan time of 0.6 s). Samples were run in full scan mode (m/z 50 to 650), and the temperature program comprised an isothermal hold at 50 °C for 2 min, ramping to 300 °C at 10° C⋅min−1, followed by an isothermal hold at 300 °C (15 min). Data acquisition and processing were carried out using HP Chemstation software (Rev. B.03.02 [341], Agilent Technologies) and Xcalibur software (version 3.0). Peaks were identified on the basis of their mass spectra and GC retention times by comparison with the NIST mass spectral library (version 2.0).
Carbon isotope analyses by GC-C-IRMS were also carried out using a GC Agilent Technologies 7890A coupled to an Isoprime 100 (EI, 70eV, three Faraday cup collectors m/z44, 45, and 46) via an IsoprimeGC5 combustion interface with a CuO and silver wool reactor maintained at 850 °C. Instrument accuracy was determined using an external FAME standard mixture (C11, C13, C16, C21, and C23) of known isotopic composition. Samples were run in duplicate and an average taken. The δ13C values are the ratios 13C/12C and expressed relative to the Vienna Pee Dee Belemnite, calibrated against a CO2 reference gas of known isotopic composition. Instrument error was ±0.3‰. Data processing was carried out using Ion Vantage software (version 1.6.1.0, Elementar). These methods have previously been detailed in, for example, ref. 39. All data discussed in this article will be made available to readers.
Acknowledgments
We would like to express our deep gratitude to Kathleen Ryan, who initially spearheaded this project. Her ethnographic scholarship on cattle pastoralism in eastern Africa continues to inspire. K.M.G. and M.E.P. thank the Tanzanian Commission for Science and Technology and the Division of Antiquities for permission to excavate at Luxmanda and to export ceramic sherds. Export permits were also issued by the National Museums of Kenya to K.M.G. for export of material from Jarigole and Dongodien. Permits for export of Ngamuriak sherds were issued to K.R. Analyses of Dongodien and Jarigole ceramics were funded by NSF Doctoral Dissertation Improvement Grant #0752042 to K.M.G. and F.M. Fieldwork at Luxmanda was funded by a University of Wisconsin–La Crosse Faculty Research Grant to K.M.G in 2015, and by a Wenner-Gren Foundation grant to K.M.G. and a National Geographic Society grant (NGS-196R-18) to M.E.P. in 2018. J.K. received a UWL Undergraduate Research Grant. Additional thanks to Natural Environment Research Council for partial funding of the National Environmental Isotope Facility (Bristol laboratory), the Leverhulme Trust (RPG-2016-115) for a research grant to R.P.E. supporting a research fellowship to J.D., the European Research Council (H2020 ERC-2018-PoC/812917) for a research grant to R.P.E. supporting a research fellowship to E.C., Helen Grant of the National Environmental Isotope Facility (Lancaster laboratory) for stable isotopic characterization of reference standards and derivatizing agents, and Ian Bull and Alison Kuhl for technical help.
Footnotes
↵1K.M.G. and J.D. contributed equally to this work.
- ↵2To whom correspondence may be addressed. Email: kgrillo{at}ufl.edu.
↵3Deceased January 17, 2018.
Author contributions: K.M.G., J.D., K.-M., K.R., and R.P.E. designed research; K.M.G., J.D., M.E.P., A.O.G., J.K., A.Z.P.M., P.R., T.G., C.W.-D., and H.L.W. performed research; E.C. contributed new reagents/analytic tools; J.D., E.C., T.G., C.W.-D., and H.L.W. analyzed data; and K.M.G., J.D., F.M., M.E.P., A.J., P.R., and R.P.E. wrote the paper.
The authors declare no competing interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.1920309117/-/DCSupplemental.
Published under the PNAS license.
References
Molecular and isotopic evidence for milk, meat, and plants in prehistoric eastern African herder food systems
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