Grass leaves as potential hominin dietary resources

Abstract

Discussions about early hominin diets have generally excluded grass leaves as a staple food resource, despite their ubiquity in most early hominin habitats. In particular, stable carbon isotope studies have shown a prevalent C component in the diets of most taxa, and grass leaves are the single most abundant C resource in African savannas. Grass leaves are typically portrayed as having little nutritional value (e.g., low in protein and high in fiber) for hominins lacking specialized digestive systems. It has also been argued that they present mechanical challenges (i.e., high toughness) for hominins with bunodont dentition. Here, we compare the nutritional and mechanical properties of grass leaves with the plants growing alongside them in African savanna habitats. We also compare grass leaves to the leaves consumed by other hominoids and demonstrate that many, though by no means all, compare favorably with the nutritional and mechanical properties of known primate foods. Our data reveal that grass leaves exhibit tremendous variation and suggest that future reconstructions of hominin dietary ecology take a more nuanced approach when considering grass leaves as a potential hominin dietary resource.

Leopard predation on gelada monkeys at Guassa, Ethiopia

“…Several million years ago, both hominins and the theropith ancestors of modern geladas transitioned from living in woodland‐dominated habitats to more open‐country environments, an environmental shift that likely presented them with novel challenges (Bedaso, Wynn, Alemseged, & Geraads, 2013; Cerling, Chritz, Jablonski, Leakey, & Manthi, 2013; deMenocal, 2011; Foley & Gamble, 2009; Isbell et al, 2018; Jolly, 1970; Pickford, 1993). These presumed challenges included a reduction in the availability of refugia (Isbell et al, 2018) and an increased reliance on resources in more seasonal, open‐country habitats, putatively including grasses and sedges (Cerling et al, 2011, 2013; Paine et al, 2018; Shapiro, Venkataraman, Nguyen, & Fashing, 2016). As a result, hominins and theropiths are both hypothesized to have adopted a fission‐fusion way of life—dispersing and re‐aggregating at irregular intervals as dictated by changing ecological conditions—ultimately resulting in the formation of multilevel societies (Chapais, 2013; Dunbar, 1993; Grove, Pearce, & Dunbar, 2012; Grueter, Chapais, & Zinner, 2012; Swedell & Plummer, 2012).…”

“…As a result, hominins and theropiths are both hypothesized to have adopted a fission‐fusion way of life—dispersing and re‐aggregating at irregular intervals as dictated by changing ecological conditions—ultimately resulting in the formation of multilevel societies (Chapais, 2013; Dunbar, 1993; Grove, Pearce, & Dunbar, 2012; Grueter, Chapais, & Zinner, 2012; Swedell & Plummer, 2012). Perhaps if, as some scholars have suggested, early hominins were constrained by similar foraging pressures to those of geladas and their ancestors (Cerling et al, 2011, 2013; Paine et al, 2018), then the evolution of multilevel societies in hominins may have provided a viable solution to handle predation risk in larger aggregations while still offering the flexibility of smaller unit foraging to cope with variations in the food supply.…”

Influences on plant nutritional variation and their potential effects on hominin diet selection

“…While trees represented the greatest biomass, the understory grasses were abundant and would have been a good source of nutrition. Our previous study of the mechanical properties of these grasses also suggests they may have been valuable foods for early hominins (Paine et al, 2018). This should be tempered, however, by our observation that the very-protein rich grasses found in Kudu Hill, notably the Setaria verticillata, were fiercely protected in the dry season by spiky panicles that clung together and would stick to any available surface.…”

Dietary versatility of Early Pleistocene hominins

“…The δ 13 C values of Homo and Paranthropus point to food intake that consisted dominantly of C 3 resources, such as forest foods, while xeric plant foods [e.g., C 4 underground storage organs (USOs), such as tubers, corms, roots, and bulbs, but also sedges, termites (20, 34, 35), or C 4 grass leaves (36)] were not dominant. However, δ 13 C data alone may not decipher C 3 and C 4 resources of dietary patterns because plant-based, meat-based, and omnivore diets cannot be distinguished with this method (e.g., ref.…”