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Strictly speaking, according to evolutionary anthropologists and archaeologists there was never a single Hominin Paleolithic diet. The Paleolithic covers roughly 2.7 million years and includes multiple human ancestors with their own evolutionary and technological adaptations. One cannot make broad generalizations of the earlier human diets as they varied dramatically across space and time. Our pre-hominin ancestors are broadly herbivorous, relying on either foliage or fruits and nuts and the shift in dietary breadth is often considered a critical point in hominin evolution. The commonality between Paleolithic diets of the various human ancestors is that they are all to one degree or another omnivorous and are inextricably linked with tool use and new technologies.

The Paleolithic Diet
The idea of an all-encompassing Paleolithic diet is a misnomer. Due to the variety of environments inhabited, physiologies of the humans and human ancestors alive during the Paleolithic over 2 million years, we can’t ascribe a single diet to any species regional or cultural group (Gowlett 2003). Increasing amounts of animal protein is viewed by some scientists as essential to the evolution of a larger human brain. Larger brain sizes required a greater caloric intake and the shift from earlier hominins is viewed as a generally greater reliance and shift to more animal protein (Aiello 2009). Meat eating was undoubtedly a factor in the increase in human brain size, but its importance in human diet cannot be assumed across all times and places, and is heavily dependent on the local environment. In colder climates meat might be necessary due to the decreased availability of plant based foods, and in hotter tropical climates a wider range of plants would be available (Gowlett 2003).

Homo habilis, Homo floresiensis & Homo erectus
By 3 million years ago the broad pattern of human dentition was in place. Reduced canines and a jaw morphology implying heavier chewing (Gowlett 2003). Stone tools and butchered animal remains dating to 2.6 million years ago have been found together in Ethiopia. This finding provides both the clearest evidence of meat eating by early human ancestors and the association of earliest stone tools with the butchering of animals for meat and marrow (Semaw et al 2003) The cooccurrence of stone tools clearly linked with the butchering of animals and earliest identifiable appearances of Homo habilis. (Ungar et al 2006). Tooth wear from Homo habilis indicates a relative lack of hard foods such as nuts, tubers or other hard brittle plant material being consumed (Ungar et al 2006, Ungar et al 2011). This is not to say that no tougher foods were eaten by H habilis, only that it was likely not a regular part of the diet. By contrast, Homo Erectus teeth generally reflect a much higher degree of wear, indicating tougher plant foods being eaten (Ungar et al 2006, Ungar et al 2011). While likely able to consume a variety of plant and animal resources, it seems that H habilis was not able to exploit the wide array of resources and ecological niches its descendants would be able to (Wood & Strait 2004).

Homo floresiensis is thought to diverged from humanities ancestral branch prior to the evolution of Homo erectus. The direct ancestor of Homo floresiensis is currently thought to be Homo habilis, but this is subject to change with new information. Tooth wear from Homo floresiensis implies a tough, fibrous diet requiring powerful mastication. There is some evidence of meat eating associated with Homo floresiensis, but current evidence indicated that a plant based diet dominated. The specific plant species available to H floresiensis is currently unknown (Brown 2009). This complicates H floresiensis relationship to H habilis due to the latter’s association with intensive meat eating diet. That being the case, more than enough time passed for H floresiensis diet to specialize to its given environment.

In contrast to Homo habilis, H erectus left its ancestral environment of Africa and spread through much of the old world. Homo erectus appears to have avoided other large predators. Several interpretations of Homo erectus diet have been made, usually contrasting between primarily plant based foragers and scavengers or opportunistic hunters. However, as H. erectus dispersed across Eurasia some behaviors in some areas appear to have changed (Carotenuto 2016). The trajectory of diets between Homo habilis and Homo erectus can be described as a diversification of diet as Homo erectus spread within Africa and beyond into Asia. Meat played a critical role in the evolution of H habilis, but as Homo erectus evolved the diet broadened to include tougher foods that H habilis did not consume regularly (Ungar et al 2006, Ungar et al 2011). A broad diet alone however is not Homo erectus sole contribution to evolution of the human lineage. Genetic evidence of reduced jaw muscles implies the adoption of cooking by humans prior to the branching of H sapiens and H neanderthalensis, placing the first use of fire for cooking firmly during the time of Homo erectus. Fire presents clear advantages to a species diet, in that cooking allows a greater range of foods to be eaten and improves the caloric content of both animal protein and plants (Perry et al 2015).

Homo Heidelbergensis & Homo Neanderthalensis
Homo heidelbergensis, the likely predecessor of Homo neanderthalensis has few direct clues to its diet. Two adult incisors, likely form H heidelbergensis have been found in England in an environment that at death would have been a spring fed wetland. The teeth themselves are heavily worn, implying heavy wear in the individual’s diet (Hillson 2010).

Neanderthals were almost certainly effective hunters. Multiple sites associated with H neanderthalensis also have the remains of butchered animals. More direct stable isotope evidence from Neanderthal bodies also indicate indicates a heavy, though by no means exclusive reliance on animal protein (Karavanic et al 2000). The degree to which Neanderthals rely on meat in their diet is extensively debated with contradictory evidence found often at very similar sites. Worn teeth from Neanderthal remains at a variety of sites imply use of plant and other abrasive foods (Kupczik & Hublin 2010), while other researchers find that Neanderthal tooth wear in general indicates a varied diet of both plants and meat (Perez-Perez et al 2003). There is clear evidence of the consumption and processing of ancestors of wheat and barley by Neanderthals from starch analysis of from dental calculus, while in Belgium, a species related to Sorghum was consumed along with other unknown plants (Henry 2010). At the site of Shanidar in Iraq, in addition to the ancestors of wheat and barley, Homo Neanderthal is known to have consumed dates, legumes and a variety other unknown plant species. In addition, evidence exists from the same teeth of Neanderthals to support the increased use of fire in their diet in addition to the wide variety of plant and animals in their diet (Henry 2010). Evidence from Neanderthal coprolites from a Middle Paleolithic site in Spain support a diet of animal protein and plants at that site, though there is a lack of indicators for the consumption of starchy tubers (Sistiaga et al 2014). Neanderthals at El Sidron cave in Spain appear to have a more limited diet of meat when compared to other Neanderthal groups. Instead of diet dominated by meat eating, the genetic and microbiological evidence from dental calculus implies reliance on mushrooms, pine nuts and a species of moss (Weyrich et al 2017). The implications of this array of evidence is important due to the evidence that the “broad spectrum” of plant use is not unique to Homo sapiens (Henry 2010). Homo neanderthalensis had, for all intents and purposes, a complex diet similar to many hunter-gather groups of Homo sapiens. The critical factor in this diet was that it varies significantly based on the local environment (Henry 2010).

Homo Sapiens
The evidence of early Homo sapiens diet stems from multiple lines of evidence, and there is a relative abundance of information due to both a larger relative population footprint and more recent evidence. A key contribution to early human diet likely was the introduction of fire to hominins toolkit. Some studies indicate a correlation with the introduction of fire and the reduction of tooth and gut size, going so far as to indicate their reduction as clear evolutionary indicators of the introduction of fire (Gowlett 2013).

A key difference between the diets of Homo sapiens and close extinct relatives such as H neanderthalensis is the ability to effectively digest cooked starches, with some evidence found linking cooked starch and a further increase in H sapiens brain size (Hardy et al 2015). Roots and tubers were introduced into the broader human diet, and can likely be associated with fire as cooking would likely be necessary for many tubers to help digest (Gowlett 2003). The use of root and tuber species in some Hunter Gatherer cultures makes up a critical component of diet. This is not only for the nutritional value of the species, but the relative annual stability of the species. This buffer effect would be important for many groups that relied on tubers (Greaves & Kramer 2014). The ability to process starch is linked genetically to modern humans, with the genes necessary to its consumption not found in H neanderthalensis. The timing of this mutation on modern humans is important as it means the ability to digest heavily starchy foods has only developed in the last 200ky years (Perry et al 2015). In addition to the exploitation of tubers, another dietary innovation (this far) of Homo sapiens is the introduction of coastal and other marine resources. Some researchers have argued that the introduction of shellfish and other marine species play a significant role in the evolution of modern Homo sapiens (Will et al 2013).

By the upper Paleolithic more complex tools and a higher proportion of meat in the human diet are assumed to correlate with an expansion of population in Europe (Bocquet-Appel 2005). Though the diet of modern humans is not consistent through the Upper Paleolithic. From the Middle to Late Pleistocene there is a general shift in many areas towards a less abrasive diet. This is accompanied by changing technologies that would aid in the processing of abrasive plant species (Perez-Perez et al 2003). Ethnographic comparisons with contemporary groups of Hunter Gatherers broadly imply a high reliance on animal protein supplemented with a wide range of available plant foods. While a reliance on animal protein is often seen as typical, it is by no means universal (Cordain 2002).

By the time of the Upper Paleolithic and modern Homo sapiens, not only was a wide variety of plants consumed, but a wide variety of animals, snails and fish as well. In order to exploit the many different species consumed, there was a wider variety of tools made than ever before available to humans (Mayer & Bar-Yosef 2009). The shift to a higher quality diet and the technology to process a wide array of foods is reflected in modern humans by both the relatively larger brain size and reduction in gut size (Kaplan et al 2000). The trend of larger brain size, the eating of animal protein, fire use and diversification of exploited foods is key to understanding the changing diets of human ancestors (Gowlett 2013).

Cannibalism
Debates over the frequency of cannibalism in ancient humanity have been sporadic, usually erupting on the discovery of human with cut and break marks reflective of being processed as food. Evidence of cannibalism has been tied to both Homo sapiens and Homo neanderthalensis. Many theories of cannibalism amongst humans rely on a lack of available prey, crowding and fears of potential starvation. There are clear biological drawbacks of cannibalism including disease, and in addition instances of ritual cannibalism that have nothing to do with nutrition drawn from the ethnographic record (Nishimura 2004). Evidence from Neanderthal remains in Belgium features cracked bones, cut marks and other indicators of processing for food. Notably, reindeer remains from the same site have the same types of butcher marks. The degree to which these remains reflect a ritual behavior, regular diet or isolated instances of dietary distress is not known (Rougier et al 2016).

General Trends
Many specifics of the evolution of the human diet are change regularly as new research and lines of evidence become available. Through the Paleolithic across the last 2.6 million years there has been a pattern of human and human ancestor’s biology adapting to a additionally available food source with resulting greater brain size, with the subsequent broadening and diversification of human diet. Homo habilis incorporated larger amounts of animal protein and fat into its diet, then as Homo erectus evolved it increased the breadth of its diet through fire and more advanced tool use. Homo sapiens in turn evolved the ability to consume cooked starch and marine life, which led to a further increase in brain size then greater technological diversification that ultimately allowed modern humans to adapt to a wide variety of ecological niches. The initial technological and biological adaptations each have knock on effects that allow a greater range of species to be used as food. This culminates in the Neolithic when suites of plants and animals are ultimately domesticated. In short, if there is a clear human Paleolithic diet, it is the use of fire to cook food (Gowlett 2003).