Evolution and Human Diet

According to plant-based proponents, prehistoric/early man mainly subsisted on fruits, vegetables, and grains and ate little, if any, meat. However, archaeological evidence suggests otherwise.

Primates vs. Humans

Plant-based proponents often point to what many scientists consider human’s closest relative, the primates, to assert that humans were and are meant to be herbivores. However, vast differences between primates and humans invalidate this argument.

In the 1995 book Comparative Physiology of the Vertebrate Digestive System, authors Stevens and Hume note how gorillas have larger colons and intestines than humans. Gorillas are hindgut fermenters, meaning, like non-ruminant herbivores, plant matter must ferment in the caecum and colon to allow bacteria to break down plant matter to absorb nutrients.

To obtain enough nutrients, primates must eat large amounts of plants daily. For example, a male gorilla eats up to 75 pounds of vegetation and fruit a day. Female gorillas need approximately 40 pounds a day.

Even with the ability to ferment vegetation and to eat massive quantities of food, this still isn’t adequate. Gorillas eat their feces, a behavior known as coprophagia, to obtain further nutrients. Despite the massive intake of plant material, their digestive system needs to process it twice to get all the needed nutrients.

Archaeological and anthropological evidence and comparison between herbivores and humans indicate that prehistoric humans were not herbivores. The ability to obtain and consume meat was vital to humankind’s development. A diet including sufficient meat is not only ancestrally correct but is species-appropriate.

Physiology: Herbivores vs. Humans

Herbivores are divided into two categories: ruminant and non-ruminant. Ruminant herbivores such as cows, have multi-chambered stomachs allowing for a longer digestive time.

Non-ruminant herbivores, such as horses or gorillas discussed above, do not have multi-chambered stomachs but have a large caecum and colon. They ferment plant matter in the caecum and colon, where bacteria break down the cellulose and carbohydrates.

As noted in a 2007 paper, humans have a “simple stomach, relatively elongated small intestine, and reduced caecum and colon.” While the human digestive system is different from pure carnivores, such as cats, who have relatively shorter digestive systems, the human digestive system relies “on a high-quality diet in which meat is a predominant component” while also being able to digest some plant foods.

Meat

After analyzing stable isotopes and trace elements of prehistoric remains found in Arene Candide Cave (Liguria, Italy), anthropologists theorize that the diet of these early humans was mostly meat, mollusks, and potentially dairy.

Trace elements analyzed were copper and zinc as indicators of meat consumption and barium, magnesium, strontium, and vanadium as indicators of vegetable consumption.

Anthropologists concludedthat the diet of the Middle Neolithic humans who lived in that area was “based on hunting and on an appreciable gathering of marine mollusks.”

Most likely, meat, fowl, and, for those populations living near bodies of water, fish and seafood would have made up the majority of prehistoric humans' diet. This is also suggested by numerous cave paintings found over the years. Such paintings have been discovered all over the world and depict hunts and images of animals. If plants were a significant component of prehistoric humans’ diet, they were not considered as important as meat.

Fat

Evidence suggests that fat was the primary energy source sought out by prehistoric man, and this led to the advanced development of the human brain.

In the 2010 book Fat Detection: Taste, Texture, and Post-Ingestive Effects, the authors note that the “human fossil record indicates that major changes in both brain size and diet occurred in association with the emergence of early members of the genus Homo between 2.0 and 1.7 mya [million years ago] in Africa” and “increased consumption of dietary fat” appears to be a vital component in the increased size of prehistoric humans’ brains.

The human brain, about three times the size of the primate brain, is the most energy-demanding organ, using approximately 20-25% of daily calorie intake at RMR (resting metabolic rate). As the brains of prehistoric humans grew, so did the need for more nutritionally dense (higher fat) foods.

Additionally, findings in the fossil record further support this hypothesis. A 2011 paper published in the journal PLoS One (Public Library of Science) highlights discoveries found in the Levant; a term that refers to the historical and geographical region of the Eastern Mediterranean region of Western Asia. Homo erectus, considered to be the direct ancestor of Homo sapiens, is speculated to have populated the region 1.5 million years ago.

The authors note how “archaeological evidence seems to associate Homo erectus with large and medium-sized game,” as the ancient remains of elephants and handaxes, “tools associated with the butchering of large game” have been found. Elephants and other large to medium-sized game would have been preferred over smaller game because of the higher fat yield.

Due to prehistoric humans increasing brain size, it is theorized this led to changes in the human gut. The gut evolved to be smaller than primates to prioritize energy for brain development and subsequent energy requirements. This shorter human gut, therefore, “had evolved to be more dependent on nutrient and energy-dense foods than other primates.”

Born To Barbeque

Humans clearly have a long history of eating a meat-heavy diet, and our digestive system is optimized for that purpose. Multiple archaeological facts intersect to show us that we evolved as scavengers and then predators. While most people are quite removed from and unaware of our collective past, a sizzling grill will still whet our appetites!