How do we know what they ate?

The foods eaten by our ancestors can tell us a lot about their lifestyles and the environments in which they lived. Food has also played a major role in human evolution, particularly when meat became a significant part of the human diet about two million years ago.

Looking at teeth shape and size

Mammals have different types of teeth used for different functions, particularly (but not always) related to eating food. For example, incisors are primarily used for cutting or ripping, canines for tearing or holding, and premolars and molars for crushing and chewing. By looking at the size and shape of a hominin's teeth, scientists can gain a clearer view about their basic diet. However, using form and structure of the teeth as a diet-predictor can be misleading, as more detailed studies (such as tooth wear or chemical analysis) indicate.

Making a mark: tooth wear patterns

Teeth are the hardest part of the skeleton but the particles in foods are still capable of leaving scratches and other marks on the surfaces of teeth. Different types of food will leave different kinds of marks. Scientists compare the marks left on fossil teeth with those found on the teeth of modern-day animals to reconstruct the prehistoric diets of our ancestors. Harder foods, such as nuts, seeds, tough fruits and tubers tend to leave small pit marks in the enamel that covers the tooth surface, whereas softer leaves and fruits leave many small scratches.

For example:

• a 2008 study on tooth wear patterns of Paranthropus boisei revealed light, wispy scratches more similar to the marks on the teeth of modern fruit eaters than those on the teeth of modern primates. This suggests that P. boisei 's huge jaw, massive chewing muscles and flat, tough teeth where not primarliy used to crush tough roots and nuts as was once believed. Tougher plants may have been used as a fallback diet when hard times meant other soft foods were unavailable.
• Australopithecus africanus skulls show tooth wear like modern fruit eaters and appears to have eaten mostly soft plant foods like fruits and young leaves. It may also have included some meat in its diet.

You are what you eat: chemical analysis of skeletons

Teeth and bones contain a protein called collagen, which absorbs chemical elements such as nitrogen, carbon, calcium and strontium from the food that an individual eats. Different types of foods contain these elements in different ratios so scientists are able to obtain information about our ancestors’ diets by studying the chemical elements found in fossilised bones and teeth. The ratios of these various elements are then compared with those of various modern-day animals to establish the types of foods eaten by our ancestors.

For example:

• Paranthropus robustus lived between 1 and 2.3 million years ago. Tooth wear analysis suggests this species mostly ate hard plant foods such as nuts, seeds, roots and tubers, typical of the African open savanna. Chemical analysis on the ratio of strontium to calcium in their teeth suggests however, that this species may have also included some meat in their diet.
• The fossilised bones of Neanderthals (Homo neanderthalensis) contain different forms, or isotopes, of nitrogen- nitrogen-15 and nitrogen-14. The high ratio of nitrogen-15 to nitrogen-14 found in Neanderthal bones is similar to that found in the bone collagen of modern-day carnivores such as wolves. This indicates that the Neanderthal diet included a large amount of meat and little plant material.

Cleaning up after dinner: the archaeological record of diet

The remains left behind after food is collected, prepared and eaten also provide information about diet. These remains include food scraps as well as the artefacts used to collect and process foods.

The chance that any remains from a prehistoric ‘dinner’ will survive varies depending on the types of food eaten. Foods with hard parts that are discarded rather than eaten (such as bones and shells) have a better chance of becoming preserved. Stone tools, bone fish hooks and other artefacts made from hard materials that do not readily decay will also preserve well. Vegetable matter, on the other hand, tends to decay more easily and is unlikely to leave any remains.

A dietary case study: the importance of meat in human evolution

Our early ancestors had diets that consisted mainly of low-nutrient plant material. This meant that they needed to spend significant amounts of time feeding in order to consume their energy requirements. The inclusion of meat in the diet was a turning point in human evolution. Eating meat provided our ancestors with more proteins and fats and higher energy levels. This allowed them to develop and sustain an active lifestyle and develop a larger brain.

When our ancestors included meat as a significant part of their diet, the effects were far reaching. These effects included:

• a reduction in tooth and jaw size, which is linked with a reduction in chewing.
• a decrease in the size of the intestinal tract and an increase in brain size.
• a reduction in the time needed for food gathering, leaving more time for learning and social activities.
• an ability to live in more varied environments than had previously been possible as herbivores. Non-seasonal animal food resources could now be utilised rather than having to rely on seasonal fruits, tubers and other plant foods with restricted ranges.

Herbivores require a large intestinal tract because vegetation is harder to digest than meat. When a greater proportion of meat was included in the diet, the digestive system was able to shrink in size and more energy became available to sustain a large brain.

Homo ergaster was the first of our extinct relatives to have a thin waist and a small intestinal tract accompanied by a significantly larger brain.

Was cannibalism practiced?

Cannibalism is the act of a species consuming other members of its own species or kind. About 15 primate species, including chimps and modern humans, have been proven to have practiced or still practice cannibalism.

Cannibalism has been known to occur in human societies in the past, and also in the modern era, in times of extreme survival stress, for ritualistic reasons, for food in general or for reasons of insanity (distinction should also be made to separate the practice of killing a human for food versus eating the flesh of a person who was already dead). The possibility that it occurred in prehistory cannot be denied, although it is difficult to prove with any certainty from the archaeological remains. Even if cannibalism did occur, it does not imply lack of emotion or respect for the victim. Anthropologists studying societies in which cannibalism was practised concluded that in some cases it was done in an effort to gain from the meal, for instance eating brains to obtain wisdom or insight, or eating flesh to gain the other person's strength.

Examining the evidence

It is necessary to first establish whether the human remains are due to animal or hominin activity. This is done by examining the bones under a microscope to see if the cut or breakage marks are from animal teeth or from tools. As the oldest tools are about 2.5 million years old this makes extrapolating any information about cannibalism prior to this time very difficult.

Once human activity has been confirmed further criteria indicating possible cannibalism are examined. These include:

• looking at the state of the bone when it was cut. Cut marks on old bones would not be for eating of meat (it would have already decayed) and may be for secondary burial practices. Cutting fresh bone may indicate using meat for consumption but may also be a sign of ritual defleshing.
• looking for the presence or absence of nutritionally valuable bones, as this indicates whether these had been chosen for consumption.
• determining if the bones of the animals and humans in the assemblage are treated in the same way
• examining the bones for breakages as this may indicate whether or not the bones were broken to extract marrow
• determining if the bones had been burnt or cooked

Examples of prehistoric cannibalism?

There is no evidence of cannibalism amongst earlier hominin species but there are some controversial examples from several Homo species, including early H. sapiens.

Homo heidelbergensis

• the Bodo skull, found in Ethiopia and dating to about 600,000 years old, shows cut marks from stone tools on the eye sockets, cheekbones, forehead and cranium. The bone was green or fresh indicating that defleshing occurred around the time of death.

Homo erectus

• Some skulls from Zhoukoudian in China show marks around the base near the foramen magnum. Although studies show some of the skull breakages were due to hyenas, analyses on Homo erectus Skull V shows marks were made by stone tools, indicating cannibalism may have occurred.

Homo antecessor

• the cave site of Gran Dolina in Spain yielded human bones, dating to about 800,000 years old, with the same types of cut marks as those on nearby butchered animal remains. This indicates dismemberment was probably the goal; the lack of carnivore teeth marks also supports the suggestion that it was humans that made the incisions.

Homo neanderthalensis

• At the site of Krapina Cave in Croatia, over 800 Neanderthal bones show evidence of cut marks and hammerstone fragments. The marrow-rich bones are missing and the marrow-poor bones are all in tact. Some argue that the evidence is inconclusive as the fragmentation of bones may have been caused by cave-ins and the bone cuts are different to the marks seen on reindeer bones. They claim the cut marks could be from secondary burial practises.
• Bones from Abri Moula in France show cut marks typical of butchery rather than simple ritual defleshing. The marks were also like those on the bones of roe deer, assumed to be food, found in the same shelter.
• The cave of El Sidron in Spain yielded hundreds of Neanderthal bones with cut marks, deliberate breaks for marrow extraction, and other signs that the bodies had been butchered for flesh in the same way as animals other bones show evidence of human defleshing and some skulls were smashed.

Homo sapiens

• some of the human bones from the site of Klaisies River Mouth in South Africa are burnt and show cut marks like those on the Bodo specimen. The cut marks were made on fresh bone.