The diet of known human ancestors varies dramatically over time. Strictly speaking, according to evolutionary anthropologists and archaeologists, there is not a single hominin Paleolithic diet. The Paleolithic covers roughly 2.8 million years, concurrent with the Pleistocene, and includes multiple human ancestors with their own evolutionary and technological adaptations living in a wide variety of environments. This fact with the difficulty of finding conclusive of evidence often makes broad generalizations of the earlier human diets very difficult. Our pre-hominin primate ancestors were broadly herbivorous, relying on either foliage or fruits and nuts and the shift in dietary breadth during the Paleolithic is often considered a critical point in hominin evolution. A generalization between Paleolithic diets of the various human ancestors that many anthropologists do make is that they are all to one degree or another omnivorous and are inextricably linked with tool use and new technologies. Nonetheless, according to the California Academy of Sciences, "Prior to about 3.5 million years ago, early humans dined almost exclusively on leaves and fruits from trees, shrubs, and herbs—similar to modern-day gorillas and chimpanzees."
Background
Due to the variety of environments inhabited, physiologies of the humans and human ancestors alive during the Paleolithic over 2.8 million years, we can’t ascribe a single set diet to any species, regional or cultural group. Larger brain sizes required a greater caloric intake. 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.
Evolution of hominins
Recents estimates of the last common ancestors of humans and chimpanzees are around 12 million years ago. After this split the first bipedal hominins appeared around 4 million years ago in the genus Australopithecus.The first appearance of genus Homo takes place around 2.8 million years ago with Homo habilis, followed by Homo erectus at around 1.8 million years ago, Homo neanderthalensis by 400,000 years ago and finally the first appearance of Homo sapiens by 200,000 years ago. In each new species of hominin, particularly genus Homo there is a general trend of increasing brain size and decreasing dentition, these patterns are inextricably linked with an evolving diet.
Lines of evidence to uncover the diet of human ancestors
There are numerous difficulties in detecting and understanding the ancient diet of human ancestors. The Paleolithic begins around 2.6 million years ago and ends only around 12,000 years ago with the onset of the Holocene and Neolithic. The enormous time scale, variable environments inhabited by human ancestors and issues with preservation ensure that direct evidence is often very difficult to come by.
Evolutionary anthropologists who study the evolution of human origins and diet use a variety of methods to determine what human ancestors ate. As a starting point comparative analysis of the diets of humans closest living relatives, great apes such as chimpanzees, bonobos and other great apes, though these comparison are limited. Through environmental reconstruction of the areas ancient humans lived, inferences of available resources can be made. A common method of analysis is through the study of dentition and toothwear, as different foods will leave different markers that can be studied. There is also direct archaeological evidence, different types of tools would be used to process and consume different types of food and often be associated with faunal remains and evidence of fire. Human coprolites can also reflect direct evidence of diet.
More recent techniques have been introduced such as carbon isotopic analysis of recovered bones, which can be used as direct evidence of diet, and life history traits. An example would be the expensive tissue hypothesis, linking a decrease in gut size with an increase in brain size. Recently genetic studies of differences between Homo sapiens and other related hominins to determine adaptations related to diet.