What is our natural diet? Are humans evolutionarily adapted to eat animals, plants or both?

| 3 June 2015
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do humans have carivore or herbivore teeth

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One of the most pervasive myths surrounding vegetarianism is the belief that humans are naturally meant to eat meat – that we are evolutionarily adapted to eat and thrive on dead flesh. A new Guide by Viva!, Wheat-eaters or Meat-eaters?, knocks this fable firmly on its head. Humans belong to the primate family. Our closest living relatives such as chimpanzees and gorillas live on a diet of foods overwhelmingly derived from plants. We ignore our evolutionary past at our peril, with the growing epidemics of killer diseases such as cancer, heart disease, obesity and diabetes now occurring in almost every corner of the planet.

Cues From The Body: We’re Wheat-Eaters, Not Meat-Eater

Basic anatomical comparisons show that people have much more in common with herbivores than carnivores – or even omnivores! Just a look at an adult’s mouth – let alone a child’s –  shows that the opening is too small for anything but relatively small pieces of food. We can’t even swallow those whole, but must chew them finely and mix them with saliva before the ball of food will slide down the oesophagus. In contrast, carnivorous animals such as cats tear off chunks and swallow them almost immediately.

Our teeth are much better suited for eating starches, fruits and vegetables – not tearing and chewing flesh. What many refer to as our ‘canine teeth’ are nothing at all like the sharp blades of true carnivores designed for processing meat.

Our jaws can open and close as well as move forwards, backwards and side-to-side. This is ideal for biting off pieces of plant matter and then grinding them down with our flat molars. In contrast, carnivores’ lower jaws have very limited side-to-side motion. They are fixed only to open and close, which adds strength and stability to their powerful bite.


A Trip Through The Body

From top to bottom, human digestive systems have evolved to efficiently process plant foods. Digestion begins in the mouth with a salivary enzyme called amylase. Its sole purpose is to help break down complex carbohydrates from plant foods into simple sugars. As there are no carbohydrates in meat, true carnivores don’t need this enzyme. Their salivary glands don’t make it.

The stomach juices of meat-eating animals are highly acidic. They have to be, so that they can break down the large quantities of muscle and bone materials they eat. Much lower concentrations of stomach acid are needed to digest starches, vegetables and fruits. Weight for weight, plant protein requires half the amount of hydrochloric acid to digest it, compared to animal protein. It is also digested in half the time. Vegans and vegetarians have fewer peptic ulcers than meat-eaters, mainly because their plant-based diets are easier to digest.

The human intestine is long and coiled, much like that of apes, cows and horses. This makes digestion slow, allowing time to break down and absorb the nutrients from plant foods. In contrast, the intestine of a carnivore, such as a cat, is short, straight and tubular. This means that flesh can be digested very rapidly, and the remnants excreted quickly, before they putrefy (rot).

The difference in transit time (time taken for food to make its way from the mouth to the anus) between humans and carnivores is what really brings the anatomical differences home. Humans – even those on a high fibre diet – have an average transit time of almost 41 hours. In stark contrast, the average transit time in a pure carnivore such as the mink, is just 2.4 hours! This means that when people eat meat, it has plenty of time to putrefy (rot) and cause the production of cancer-causing agents.

We cannot make vitamin C – we need it in our diet. Carnivores and omnivores manufacture it internally.


Handy Man

Finally, take a look at the external differences. Our hands are made for gathering plants, not for ripping flesh. We cool ourselves by sweating, like most other plant-eating animals, rather than panting like carnivores. We drink by sipping, not by lapping like a dog or cat.


Back To Our Roots

Fruits, green leafy parts of plants, shoots, seeds, nuts, roots and tubers are the fundamental components of the primate eating pattern – and common sense tells us that these foods should be the foods that humans eat, too.

Our Stone Age predecessors ate three or more times the amount of plant foods that we do – about nine servings daily of fruits and vegetables, compared to the UK average of three. And we consume just a fraction of the antioxidants, calcium, iron and other nutrients that our ancestors ate every day.


Cholesterol Calamity

It is well known that too much cholesterol is harmful to the human body. What is less widely known is that cholesterol is only found in animal foods, and not plant foods.

Meat-eating animals have an unlimited capacity to process and excrete cholesterol from their bodies. For example, you could feed a cat egg yolks all day long, and he or she would excrete all of it, never suffering from a build up of cholesterol. On the other hand, people’s (like other plant-eating animals) livers have a very limited capacity for cholesterol removal. Most people have great difficulty eliminating the amounts of cholesterol that they take in from eating animal products. We were made to consume plant foods (containing no cholesterol); therefore we have never needed a highly efficient cholesterol-eliminating system.


Meat-Eating Chimps?

It has passed into popular folklore that chimps have been observed eating meat, which has been taken as an indication that humans too have evolved to eat meat. This is in large part due to a David Attenborough film many years ago in which chimps were seen hunting. Attenborough’s observations were first recorded by chimpanzee expert Jane Goodall. Over 10 years, the 50 or so chimpanzees killed and ate 95 mammals. They were all tiny – the young of bushpigs, bushbuck and baboons – and most weighed 10lbs or less. It works out at 2.4 grams per individual per day – about the size of a pea! So, meat-eating in chimps is actually rare – it forms just 1-1.5 per cent of the overall diet. And, of course, not all chimp groups hunt at all.

Whilst our primate ancestors did eat insects this was not in sufficient quantity to provoke a change in their dentition. Primate canine teeth are small and their molars have a large grinding surface with a thick enamel covering, making their jaws a powerful crushing, grinding and chewing machine designed to cope with vegetation.

Of all the living primates, humans are the only one to eat large animals, the rest being almost entirely herbivorous.


Back In Time

Sixty million years ago the lower primates first developed – the mammals from which we all sprang. So much of what makes us skilled as mammals was developed at this time. They were all plant-eating species.

Twenty million years after the lemurs came the anthropoids, the higher primates that include monkeys, apes and humans – another group of vegetarians. Around 18 million years ago came the hominoids, apes which lack tails and have larger brains and bodies than the monkeys. They evolved in Africa and included one called Proconsul, sometimes referred to as the ‘Daddy of us all’. It is thought that we share this ancestor with the gorilla and it is another famous vegetarian. DNA studies show that we have a close relationship with the gorilla and the chimpanzee and that we split from one common ancestor around five to six million years ago.

Because we have the fossilised jaws to study, we know that these primates were herbivores and ate fruits, nuts, berries and the cambium which grows in the spring beneath the bark as the tree begins to swell. Some of us still eat it today and we call it slippery elm, a popular health food supplement for digestive disorders.


Meat-Eating Beginnings

Meat-eating began in the last one-and-a-half million years with the advent of Homo erectus, who lived until 300,000 years ago. However, this species was still largely a plant-eating animal. Contrasted with the life of an 80-year-old human being it means that only in the last 15 years would meat have been eaten. For 65 years we were vegetarian.

Of course no-one can deny that human beings became omnivorous. But very little meat was eaten compared to today’s consumption. Hunting was given a great boost when climactic changes destroyed the food sources in the northern climes in the great Ice Ages. However in evolutionary terms this is a very short period.

Humans are naturally vegan and we ignore, at our peril, our primate ancestry. The sooner we ditch the ‘meat maketh man’ myth the better for our health. We were never meant to eat meat or dairy (which humans only began consuming 6,000 years ago), our bodies are not designed to eat flesh and our health is suffering because of it. Once we exclude animal products from our diets our own health, our planet’s health and the lives of billions of animals will be better for it. Only then can we really claim to be a truly great ape.

Extracted from the Viva! Guide, Wheat-eaters or Meat-eaters?. Buy it for just £1 inc p&p. Call 0117 944 1000 (Mon-Fri) or send your name and address with cheque to ‘Viva!’ to Viva!, 8 York Ct, Wilder St, Bristol BS2 8QH



Comparative Anatomy Chart: Carnivores, Herbivores, Omnivores and Humans

Facial muscles

Reduced to allow wide mouth gape

Well developedReducedWell developed
Jaw type

Angle not expanded

Expanded angleAngle not expandedExpanded angle
Jaw joint location

On the same plane as the molar teeth

Above the plane of the molarsOn the same plane as molar teethAbove the plane of the molars
Jaw motion

Shearing; minimal side-to-side motion

No shear; good side-to-side, front-to-back motionShearing; minimal side-to-side motionNo shear; good side-to-side, front-to-back motion
Mouth opening vs head size


Teeth: incisors

Short and pointed

Broad, flattened and spade shapedShort and pointedBroad, flattened and spade shaped
Teeth: canines

Long, sharp and curved

Dull and short or long (for defence), or noneLong, sharp and curvedShort and blunted
Teeth: molars

Sharp, jagged and blade shaped

Flattened to grind foodSharp blades and/or flattenedFlattened to grind food

None; swallows food whole

Extensive chewing necessarySwallows food whole and/or simple crushing


About the author
Juliet Gellatley
Juliet Gellatley is founder & director of Viva! – the biggest vegan campaigning charity in Europe. Viva! launched in 1994, joined by Viva! Poland in 2002. Juliet has created and launched numerous campaigns on the impact of what we eat on animals, the planet and our health. She has also investigated many farms – often the big names - and exposed the devastating cruelty. She is the author of several reports, guides and books and producer of the award-winning HOGWOOD: a modern horror story documentary on Amazon Prime. Juliet has given many hundreds of talks, radio, Podcast and TV interviews. Juliet has a degree in Zoology & Psychology and is a qualified nutritional therapist.

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