Diet and Human Evolution: What Did We Evolve to Eat?

There is a lot of confusion today about what makes up a healthy diet. According to proponents of the Paleo diet, we should eat only what our earliest ancestors ate. But do we know what their diet was? And can we access those foods today? This article explores some of what we know—and don’t know—about diet and human evolution.



 homo erectus

Who Were Our Ancestors?

The consensus today is that modern humans evolved in Africa and expanded from there in the past 200,000 years. Our nearest living relatives are chimpanzees and bonobos, with whom we had a common ancestor 7 million years ago. More recent ancestors include: 

  • Australopithecus afarensis (“Lucy”, 3-4 million years ago) 
  • Homo habilis (first toolmaker, 1.6-2.3 million years ago)
  • Homo erectus (first to leave Africa, 0.7-1.5 million years ago)
  • and Homo heidelbergensis (0.2-0.8 million years ago).

Neanderthals are a side branch of our lineage. However, Neanderthals interbred with Homo sapiens outside Africa, as did the Denisovans, another human species known only from two fossil bones in Siberia.

Modern Homo sapiens probably left Africa via the Arabian Peninsula around 70,000 years ago. They moved out along shores since flooded by rising seas, reaching Australia by 50,000 years ago. Some moved inland to Europe 40,000 years ago. There they encountered the Neanderthals, over-running their territory and replacing them. Others colonized the Americas via the Bering land bridge around 15,000 years ago. The Pacific islands were settled last, some only in the past 1,000 years.



cave fire

What Did Our Earliest Ancestors Eat?

The great apes are a good starting point to understand diet and human evolution. Chimps and bonobos eat mainly plant foods such as fruit and leaves. They occasionally take in animal food by collecting insects or hunting monkeys. They have large teeth to break up a fibrous diet and spend much of the day chewing. These apes also have a large gut in which microbes aid digestion. 

Our earliest ancestors probably followed an ape-like diet. But by the time of Homo erectus, there are signs of change. The fossils show smaller teeth, weaker jaws and a reduced gut size. Brain size also increased, even though brains are costly to fuel. Humans had started moving to a diet that was more energy-rich and easier to digest. Four factors probably drove the change:

  • more meat eating
  • use of fire
  • eating starchy roots, and
  • better food processing

The relative timing of these factors is not settled, but all played a role. Cut marks on fossils show carcass processing going back at least 2 million years. Cooking has become essential: humans now have trouble maintaining weight on a raw diet. We have more starch-digesting enzyme in our saliva than chimpanzees, so starch was important to survival. Finally, Homo erectus made more complex tools than earlier species. Cutting meat, cracking nuts and grinding plant foods could all have played roles in a more digestible diet.



evolve to eat

Out of Africa

Expanding from Africa was a huge step. We had to adopt highly flexible behaviour to survive in new geographical regions. Migration itself drove even more change: the visible differences between non-African populations have all arisen in the past 70,000 years.

Moving into new areas meant eating novel foods. We digest meat or fish readily, but new prey could be difficult or dangerous to obtain. In addition, wild game is very lean, and protein alone does not support human life. In the absence of a ready source of fat, or when the hunt failed, hunters needed plant foods.

Unlike meat, plants can be hard to digest. Compared to apes, humans have lost much of the ability to obtain energy from leaves. An alternative is starch, stored in plant roots or seeds. Our gut converts starch to glucose, especially if cooked. We can also use fructose and sucrose from fruit for energy. But many plants are bitter or toxic, needing special processing to make them edible. In each new habitat, our ancestors had to learn anew what foods they could eat. In some cases, there are clear links between diet and evolution. With limited access to plants, Inuit in the Arctic ate a high-fat, high-protein diet based on marine animals. Their genes now show changes that protect against high fish oil intake. They also have cold-adapted genes that may have come from Denisovans.




The Start of Agriculture

The upheaval that came next was not planned. Foragers collected their favourite plants and discarded seeds or roots near camp sites. They chose fruits that were sweeter or less bitter, wild grasses with seeds that were easier to mill into flour or roots were starchier and less fibrous. Returning to old sites, foragers sometimes found improved stands of plants and again chose the best to eat. Bit by bit, plants were accidentally domesticated, and later deliberately planted near permanent villages. Farming started in multiple locations up to 10,000 years ago. The plants varied: grains (teff, sorghum, millet), roots (cassava, taro) and fruits (olive, fig), but all became radically different to their wild relatives. In parallel, some herd animals were tamed and came to be managed as a regular supply of food.

Once agriculture began, it spread across huge areas. Farmers out-competed their neighbours, who either adopted agriculture or were forced into less fertile regions. On an agricultural diet we bred faster, despite more disease in permanent villages. For this reason, nearly all of us today are descended from farmers. Links between diet and evolution are evident again here. If your ancestors kept cattle for milk, you may have genes to digest milk sugar as an adult. Maasai herders, consuming largely milk, meat and blood, have genes both for milk digestion and to protect against a high-fat diet. If your ancestors farmed starchy crops, you may have saliva that digests starch more readily, and this may help protect against diabetes



healthy diet

Lessons for a Healthy Diet Today

Can we use information about diet and human evolution to prescribe how to eat today? Not really. There are three problems:

The first is that we lack detail about our ancestors’ diets. To a large extent, we can only speculate about what prehistoric hunter-gatherers ate or how their diet varied over time or between different areas. There is some data on recent hunter-gatherers, but even that is disputed. Dietary extremes like those of the Inuit or Maasai also raise questions about whether there was ever a single typical “paleo diet”.

The second is that we can’t assume hunter-gatherers had optimum health. As with diet itself, we have limited data. Gene variants relating to diet show survival on the available foods could at least be challenging. In addition, while hunter-gatherers may have had low rates of Western disease, so did primitive farmers cultivating a limited number of crops. Farming itself may not be the issue.

The third problem is: even if our ancestors had a single ideal diet, we cannot follow it today. The foods they ate are not available to us, or cannot feed our populations. We can plant maize, but we cannot survive by gathering wild teosinte. Our domestic plants and animals differ nutritionally from their wild relatives in significant ways. Hence, a diet constructed from these foods would not be our ancestral diet.

So are we doomed? Not remotely. We may know relatively little about what our ancestors ate, but we know more than ever about a healthy diet. There are detailed studies on how diet affects heart disease, the genetics of obesity and the importance of our gut microbiome. If we are careful to take in quality information, we have every chance to eat for good health—and a longer life than our ancestors ever enjoyed.

Bon appétit!



Further Reading

Catching Fire: How Cooking Made Us Human, Richard Wrangham, Basic Books, Philadelphia 2009

Guns, Germs and Steel: A Short History of Everybody for the Last 13,000 Years, Jared Diamond, Vintage Publishing, London 1997

Paleofantasy: What Evolution Really Tells Us About Sex, Diet, and How We Live, Marlene Zuk, Norton, New York 2013

The 10,000 Year Explosion: How Civilization Accelerated Human Evolution, Gregory Cochran and Henry Harpending, Basic Books, New York 2009