In Jean Auel’s The Valley of Horses, Ayla faces a problem that at first seems strange. She can catch small animals such as rabbits, so she has meat. Yet she remains desperate to kill a larger animal because she needs fat.

Why would that matter so much? If a person has plenty of meat, shouldn’t that be enough?

The answer is no. In a cold environment, especially during a long winter, obtaining enough food and obtaining the right kinds of food are two different problems.

Humans need protein, but we cannot simply keep increasing protein intake indefinitely to meet all of our energy needs. A diet composed overwhelmingly of very lean meat can become dangerous. Early explorers sometimes called the resulting condition “rabbit starvation.” Modern nutritional research describes the same underlying problem as excessive protein intake combined with too little fat or carbohydrate.

That makes Ayla’s search for fat much more understandable.

Meat Was Not All the Same

When we say that prehistoric people ate meat, it is easy to picture something resembling a modern steak. But an animal offered much more than muscle.

A successful kill could provide:

  • muscle meat
  • fatty tissue
  • bone marrow
  • organs
  • blood
  • brains
  • connective tissue

From a survival standpoint, these parts did not have equal value.

Lean muscle supplies large amounts of protein. Fat supplies concentrated energy. Gram for gram, dietary fat contains more than twice the energy of protein or carbohydrate.

For someone trying to survive winter, that mattered enormously.

A rabbit can provide useful protein, but wild rabbits are often quite lean. A large ungulate or other substantial animal could provide stores of fat unavailable from small lean game. Even when the visible meat itself was lean, marrow and particular body tissues could remain valuable sources of energy.

The problem could become especially serious late in winter. Archaeological research has pointed out that hunter-gatherers in temperate, subarctic and arctic regions sometimes encountered a difficult combination: stored foods were running low at the same time that hunted animals themselves had lost much of their body fat. Under those circumstances, people could have plenty of lean protein available and still struggle to obtain enough usable energy.

The Problem With Living on Lean Meat

Protein is indispensable. It provides amino acids needed to build and repair tissue and perform countless other functions.

But using protein primarily as fuel creates another problem. The nitrogen contained in amino acids must be processed by the liver and excreted.

There appears to be a practical limit to how much protein the human body can handle. Reviews of human protein intake describe very high-protein diets as capable of producing nausea, diarrhea and other serious effects when protein becomes an excessive share of total calories.

That helps explain the old accounts of “rabbit starvation.”

A person could eat repeatedly, feel hungry again soon afterward, eat more lean meat and still fail to solve the underlying energy problem.

The missing ingredient was not necessarily more meat.

It was often fat or carbohydrate.

Why Fat Was So Valuable

Fat solved several problems at once.

First, it is extraordinarily energy dense. Someone living outdoors in freezing temperatures, walking long distances, hunting, gathering fuel and maintaining shelter could burn tremendous numbers of calories.

Second, fat allowed people to obtain those calories without forcing the body to process ever-increasing quantities of protein.

Third, dietary fat supplies essential fatty acids that the human body cannot manufacture on its own.

This means that a large animal was valuable for reasons beyond the sheer quantity of flesh hanging from its skeleton.

A successful hunter would have strong reasons to value the fatty parts of the carcass.

It also helps explain why bone-breaking appears repeatedly in archaeological sites. Bones are not empty packaging surrounding the meat. They can contain marrow—an energy-rich resource worth recovering.

The concept changes the way we think about hunting. The goal was not necessarily to obtain the largest possible pile of meat.

The real goal was to obtain nutrition.

But People Needed More Than Fat

It would be equally misleading to go to the opposite extreme and imagine that prehistoric people required nothing but fatty meat.

Humans are extraordinarily flexible eaters.

When available, carbohydrate could be extremely useful. Research examining lean-meat diets found that both fat and carbohydrate improve the nutritional situation, and carbohydrate can be particularly effective at reducing the amount of protein the body must burn for energy.

Depending on region and season, hunter-gatherers could make use of foods such as:

  • roots and tubers
  • nuts
  • seeds
  • berries and other fruits
  • fish
  • shellfish
  • edible inner bark and other plant foods
  • preserved foods gathered during more productive seasons

Not every population had access to all of these foods, and winter diets differed enormously by environment.

That is an important point. There was never a single “Stone Age diet.”

People living near a productive coastline faced a completely different food environment from people living on an inland steppe or in a northern forest.

Winter Was a Problem People Planned For

One of the mistakes we can make when imagining prehistoric life is assuming people simply waited until they became hungry and then went looking for something to eat.

Survival in strongly seasonal climates required planning.

Food could be dried, smoked, frozen, cached or otherwise preserved when conditions permitted. Nuts, roots and other plant foods could sometimes be gathered before winter and stored.

Human movement itself was another strategy.

People did not necessarily remain in one place throughout the year. Winter survival could involve months of preparation, food storage, knowledge of animal movements and decisions about where to spend the cold season.

What About the Mountain Men?

The mountain men of the early nineteenth century provide an interesting later comparison.

They were not prehistoric hunter-gatherers. They possessed firearms, metal traps, horses, trade networks and access to manufactured goods. We should not treat them as substitutes for early humans.

But they faced one problem that would have been immediately recognizable thousands of years earlier:

How do you stay fed through a Rocky Mountain winter?

Historical accounts show that starvation was a real danger. Large animals were extremely important, and descriptions of winter food sometimes specifically emphasize fat meat.

But mountain men were not necessarily living on meat alone.

The annual rendezvous connected trappers with commercial supply networks, and trade goods could include foods such as salt and sugar along with other supplies. Fur-trade posts could also produce or receive agricultural foods.

The surviving records are uneven, especially for men traveling alone or in very small parties. That makes it risky to construct one universal “mountain man diet.” Some undoubtedly depended heavily on game for long periods. Others had access to trade goods, stored foods or settlements at different times of the year.

But the underlying nutritional problem remained the same.

A man could kill an animal and still care deeply about whether that animal was fat.

Survival Was About More Than Finding Something Edible

This may be the most interesting lesson.

Early humans did not merely face the question:

Can I find something to eat?

They also faced:

Does what I can find contain what my body actually needs?

A landscape filled with rabbits might still present a nutritional crisis.

A large animal could be worth enormous effort because it provided access not just to meat, but potentially to fat, marrow and nutrient-rich tissues.

Roots gathered months earlier could become critical during winter.

A cache of dried food could mean the difference between remaining in a good shelter and being forced to move during terrible weather.

And generations of experience would have taught people where particular foods could be found, when animals became lean, which parts of a carcass were most valuable and what needed to be stored before winter arrived.

Ayla’s predicament is fictional.

The nutritional problem behind it is not.

For much of human history, survival meant understanding something modern people can easily forget:

Calories were important—but the source of those calories mattered too.

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