Stone Age Sustenance: How Meat and Animal Fat Shaped Paleolithic Diets

The short answer is “no, but...” What people eat has always varied by region, season, and ecology. However, such flexibility does not cancel the evolutionary constraints that still apply. Even as opportunistic eaters, humans cannot freely consume foods outside the range their biology can handle without suffering the costs. For nearly every other animal, we assume it will thrive on a diet that roughly matches the one it evolved to eat. Humans are unlikely to be an exception. 

The question, then, becomes: how to mark the boundaries of that human, species-adapted dietary range, variable though it is? To answer that, we need to know what our ancestors ate during the evolutionary time span of the Stone Age, ever since they moved into the savannah. 

Before 4 million years ago, carbon-isotope evidence indicates diets that were still dominated by woodland plants. Forest-dwelling hominins relied mainly on fruits, leaves, pith, and maybe underground roots and tubers, occasionally supplemented by insects and small vertebrates. 

Only later, as African landscapes became more grass-dominated between 4 and 2 million years ago, did a fundamental dietary transition take place. Aggressive scavenging of animal carcasses became important, supplying grassland-derived nutrients, in particular those from flesh, fat, marrow, and organs, at first probably in modest amounts. Although this shift in ecological niche did not immediately produce full-blown hunters, meat and animal fat became increasingly important.

There is no well-defined moment, but divergence accelerated once hominins gained access to large herbivores. The older idea that aggressive scavenging of cadavers allowed hominins to become sufficiently efficient to threaten competing predators, after which they transitioned to active hunting, now looks too simple. Carrion remained valuable later on, especially in seasonal shortages, while there was less competition with other animals than often assumed. In contrast to carnivores, early hominins focused on inside-bone nutrients (brains and marrow), which carried less microbial risk.

That said, hunting became the main source of meat as Homo emerged from Australopithecus. The earliest stone-tool marks on megafauna date to 1.8 million years ago, on modified elephant bones, as marrow helped fuel larger brains in Homo erectus. By then, early humans appear to have specialised in megafaunal resources, with major consequences for social organisation.

Meat, viscera, and animal fat supplied abundant energy, fat, complete protein, and micronutrients. They were essential for brain expansion and produced the adaptations that set humans apart from other apes: taller, more linear bodies; smaller teeth and chewing muscles; and a ribcage and pelvis that imply a reduced gut. The expensive-tissue hypothesis holds that a shorter, less fermentative gut could be sustained only on a higher-quality, more digestible diet, freeing energy for a larger brain. From that point on, scavenging, hunting, and fishing remained vital for nutrient security through the Pleistocene.

The dependence on animal foods likely began in infancy. Human infants are born with large, costly brains and delayed dental development. Breast milk alone cannot meet the iron, energy, and long-chain fat needs of later infancy, and Palaeolithic groups had no porridges or milled staples. Caregivers must have pre-chewed meat and fat for older infants and young children. Without that practice, it is hard to see how the nutrient demands of brain growth could have been met.

One million years ago, during the Middle Pleistocene Transition, Homo erectus populations expanded into various African and Eurasian steppe-desert regions and beyond. To improve dietary breadth, early humans relied on social cooperation and, especially, technological innovations. Large ungulates often became a dietary staple, which was facilitated by the use of wooden spears. In arid or icy environments, where plant resources were limited, humans relied heavily on large animals, prioritising fatty cuts of meat. Fishing and shellfishing appear in some regions by the later Pleistocene and, in a few places, much earlier. In tropical regions, diets incorporated more fruits, tubers, seeds, and nuts, while coastal populations included seafood and marine fats. 

Notwithstanding their place in the large-carnivore guild, the preferred dietary targets of Palaeolithic humans were foods rich in carbohydrates and, above all, lipids, whether of animal or plant origin. The sources of these macronutrients, and their relative proportions, were governed by availability and culture rather than by biology. Adequate fat and/or carbohydrate intake was required to avoid protein poisoning, a condition sometimes described as 'rabbit starvation'. Lean game such as rabbit is high in protein and very low in fat, so a diet based on it can leave a person both underfed and protein-overloaded. This is why Palaeolithic hunters targeting large herbivores, in the absence of starchy or sugary foods, are thought to have preferred marrow, brains, and fatty tissues rather than lean muscle.

During the late stages of the Pleistocene, into the Mesolithic era, humans adapted to new ecological challenges during the Broad Spectrum Revolution. Well before the woolly mammoth went extinct in Europe about 12kya, modern humans already started creating predatory pressure on the megafauna. This created a need to hunt for smaller and faster animals, thus selecting for more agile and cognitively developed hominins. Diets were diversified by including more eggs, fish, seafood, and plants. A shift toward smaller game required greater precision, planning, and cooperation, advancing social complexity and innovation. Long-range weapons and improved thermal and non-thermal food processing techniques also enhanced food security.

The capacity to exploit a wide diversity of animal and plant foods through processing marked a major threshold in hominin evolution, contributing to their capacity to conquer new environments. In its crudest form, this involved the use of stone tools. Slicing meat already reduced chewing time and force well before cooking became routine. Even raw, animal foods would have lowered the cost of feeding a growing and metabolically expensive brain. 

The use of fire definitely was a game changer, boosting the adaptive potential of early humans. Controlled fires date back at least 800,000 years, and fundamentally shaped social organisation. Its use progressed from harvesting natural fire to maintaining and ultimately making fire, which was achieved at least 400,000 years ago. Cooking dramatically improved the net energy value of plant and animal foods by facilitating mastication and increasing digestibility.

Besides slicing and cooking, fermentation and other forms of processing improved the safety, digestibility, and nutrient availability of foods, diversifying diets even within similar environments. Seasonal scarcity also mattered: in leaner periods, groups depended more heavily on stored or preserved foods. For instance, given the efforts needed to process large animals in cold periods of the Eurasian Palaeolithic, various ways of storing and preserving vast amounts of meat and fat were probably used (alternatively, humans could have temporarily aggregated in short-term larger group sizes). Ways of preservation may have included drying, smoking, fermentation, and ‘pond’ storage in water. ‘Putrified’ meat and fish were likely ubiquitous, desirable, and nutritionally important.

Probably 30-70% of the caloric intake came from animals, but this may have been higher in areas with mega-herbivores and during glacial conditions. Homo habilis likely consumed only around 10%, being still close to the Australopithecus lineage. For the obligate bipedal and larger-brained Homo erectus, arguably the first true representative species of Homo, the contribution may have been 60% or more, and for Homo neanderthalensis even up to 80%. 

It has been argued that Homo members may have been, at least for a part of their existence, megafauna-chasing ‘hypercarnivores’. At least some of the Upper Palaeolithic diets became dominated by red meat and fat, with mammoth protein comprising up to two-thirds of the intake of Neanderthals and early ‘modern humans’ in certain regions of Eurasia, followed by other large animals, such as bison, aurochs, muskox, reindeer, horse, and woolly rhinoceros. A 10-metric-ton straight-tusked elephant would have easily yielded more than 2,500 daily portions of 4,000 kcal for adult Neanderthals.

These diets seem to have been mostly terrestrial, lacking contribution of aquatic sources. Even if landscapes and food sources may have been more diverse and with higher access to plants than often assumed, even in extreme cold conditions, populations were mostly heavily carnivorous in the presence of megafauna. As an example, the more recent Clovis culture may have obtained up to 95% of calories from large herbivores, such as mammoths, elk, and bison. Their diet was similar to that of Homotherium, a now-extinct scimitar-toothed cat.

However, after the megafauna extinction at the end of the Pleistocene, humans were pushed into a new major dietary transition. Especially during the Mesolithic ‘Broad Spectrum Revolution’, diets became more diversified with a focus on smaller animals, while more sophisticated processing enhanced the role of foods like tubers and grains. Macronutrient ratios differed based on ecological factors, with some diets being low in carbs and high in protein, while others incorporated more starches. Eventually, this would lead to the agricultural transition in the Holocene.

In any case, animal-sourced foods were essential in all pre-agricultural diets. Even modern foragers still derive more than half of their energy from hunting and fishing on average. In cold environments, this even reaches higher shares (>90%), while the caloric budget is dominated by plants for only a minority of groups. Meat and animal fat consumption ranges from 5% to 90% of total caloric intake, with annual intake levels of 40-650 kg per person, depending on the group and region.

When we talk about a ‘natural’ diet, we are not talking about a fixed menu but about an ever-changing buffet tailored by time and place. Designing an optimal ‘Paleo’ diet would be an illusion, not in the least because today's foods are no longer representative of the ancestral situation. 

That said, there are some physiological boundaries that need to be respected. Understanding evolutionary diets and the biological limits of human nutrition can clue us in on what is good for us and what is not. Such knowledge also helps keep modern misconceptions about food in check. Animal nutritionists seem to understand this much better than many human nutritionists and dietitians, possibly because the former are more prone to reality checks.

For instance, it is wrong to argue that today's consumption of red meat and animal fat is ‘unnatural’ or ‘unprecedented', even in wealthy countries. During 99% of human existence, our ancestors likely consumed more of these foods per person than we do now. Moreover, the ability to thrive on plant-heavy diets long-term is not universal. It varies with genetic differences in lipid metabolism, brain function, and the conversion of plant precursors into bioactive forms. Notably, APOE ε4 carriers appear more dependent on animal-derived nutrients, likely a legacy of ancestral hypercarnivory, which can contribute to health issues in modern low-meat environments.

It is for these reasons and nuances that Palaeolithic diets should not be seen as blueprints, but as a source of inspiration. They allow us to identify what is biologically relevant (or not) and to formulate more robust dietary guidance. The Nourishment Table is an example of such an approach.