Margaret Schoeninger describes how stable isotopes tell us that humans and neanderthals were likely high level carnivores.
Stable Isotope Analyses and the Evolution of Human Diets
Stable Isotopes Mammal Bone Collagen 13C 15N
Using stable isotopes to estimate date and diet.
Diet, Evolution, Extinction, Hunting
Facultative Carnivore describes the concept of animals that are technically omnivores but who thrive off of all meat diets. Humans may just be facultative carnivores - who need no plant products for long-term nutrition.
Hunter-gatherer societies refer to a way of life that prevailed for most of human history, where people relied on hunting wild animals, fishing, and gathering edible plants, fruits, and nuts for their subsistence. This lifestyle was common before the development of agriculture around 10,000 years ago.
Abstract Stable isotope analysis of carbon and nitrogen has revolutionized anthropology’s approach and understanding of the evolution of human diet. A baseline comparison across extant nonhuman primates reveals that they all depend on C3 plants in forests, forest patches, and woodlands except during rare seasonal intake, in marginal regions, or where maize fields exist. Even large bodied hominoids that could theoretically rely on hard-to-digest C4 plants do not do so. Some Plio-Pleistocene hominins, however, apparently relied heavily on C4 and/or CAM plants, which suggests that they relied extensively on cecal-colon microbial fermentation. Neanderthals seem less carnivorous than is often assumed when we compare their δ15Nbone collagen values with those of recent human populations, including recent human foragers who also fall at or near the top of their local trophic system. Finally, the introduction of maize into North America is shown to have been more sporadic and temporally variable than previously assumed.
One of the most interesting and confounding applications of stable isotope ratios has been the study of Neanderthal δ15Nbone collagen values. On the basis of nitrogen data, authors suggest that Neanderthals ate virtually no plants or were highly carnivorous (Balter & Simon 2006, Hublin et al. 2009), predominantly ate meat (Richards & Schmitz 2008, El Zaatari et al. 2011), or obtained their protein solely from meat (Richards et al. 2008), especially large herbivores (Richards & Trinkaus 2009). Some have even suggested that Neanderthals might have differed physiologically from modern humans in order to digest such large amounts of meat (Pearson 2007). Complete carnivory in extant primates occurs only in Tarsier, which weighs ∼100 g and has distinct morphological adaptations that allow it to obtain and survive on such a diet (Fleagle 2013). Some foraging human populations such as the Dogrib, a Dene Aboriginal Canadian people living in the northwestern part of Canada, survived on almost 60% animal products (Szathmary et al. 1987), as did other human foragers living far from the equator (Kelly 1995, Cordain et al. 2000). All these groups, however, included significant amounts of plant foods and/or animal fat, and there may be a protein ceiling of ∼35% (Cordain et al. 2000) because higher levels compromise liver function owing to physiological limitations on urea synthesis (Speth & Spielmann 1983, Hardy 2010). In part, the assumption of carnivory is based on the expectation that Neanderthals lived under arctic conditions with few available plants. Yet, many Neanderthal sites are in more southern parts of western and southern Europe (Shipman 2008 and see included references), and Europe experienced temperature fluctuations, including warm intervals, during Neanderthal times (Hardy 2010). Evidence from dental calculus indicates that Neanderthals ate some plants (Henry et al. 2011, Salazar-Garcia et al. 2013), and edible plants were recovered from the Neanderthal site of Amud, Israel (Madella et al. 2002). Richards & Schmitz (2008) concluded that high carnivory was based on the similarity between Neanderthal values (9 and 7.9) and those of a red fox (8.6), even though red foxes are noted to be omnivores (Lloyd 1981). Figure 2 compares all generally accepted European Neanderthal δ15Nbone collagen values compared with European hyena, horse, and reindeer (Bocherens et al. 1991, Bocherens et al. 1999, Richards et al. 2000, Bocherens et al. 2001, Bocherens et al. 2005, Richards et al. 2008, Richards & Schmitz 2008). Although Neanderthals have the highest δ15Nbone collagen values, the overlap between individual Neanderthal δ15Nbone collagen values and those of hyenas is extensive (10.1–11.8 in the former and 7.9–11.5 in the latter). This is the same pattern seen in North American Great Basin human foragers (see Figure 2) and four additional trophic systems (Schoeninger 1995b). High relative δ15Nbone collagen values are common in humans, although it is far from clear how this result occurs. Neanderthals clearly ate meat just as human foragers worldwide do (Kelly 1995, Speth 2006); they selected prime adults and the bones most likely to contain a lot of marrow (Gaudzinski & Roebroeks 2000). Some data also suggest that they hunted marine mammals (Stringer et al. 2008), which often have much fat. Such selection would allow them to eat animal products for up to two-thirds of their diet. But, the question is, did they? Or, perhaps more realistically, did they all participate, and if so, when? Only after we understand why humans almost always have high δ15Nbone collagen values can we address these questions fully.