Science101
WHY HUMANS ARE NOT DESIGNED TO EAT MEAT
– A long overdue science lesson
What we are taught at school. Unfortunately, the National Curriculum does not have much to say about the human diet. Most school children seem to learn just three facts. 1) Humans are omnivores - we can eat anything; 2) Canine teeth are proof that we are supposed to eat meat; 3) Milk is full of Calcium, drink it up. A textbook illustration will show the human digestive system next to that of, say, a dog and a sheep. A cursory glance reveals that humans are somewhat intermediate in form. It sensibly follows that our diets should also be intermediate – we can eat anything - go forth children, and overpower those edible beasts! This is generally the extent of formal education on this matter, and it does seem decidedly odd that we are not taught further about our own bodily functions and the food we should be eating to maintain health.
It is true that the majority of people eat meat in addition to plant-based foods. Therefore to describe humans as omnivores is a statement of fact. However, most humans eat unsuitable foods on a frequent, often daily basis. Just because the majority of humans happen to be omnivores does not in any way support the notion that this is the most appropriate diet for our bodies. Food consumption should involve important decisions each day. It may sound like an old cliché, but quite literally, you are what you eat. You have the capacity to choose food that contains all the vital nutrients required to help you to function healthily… or you can fill yourself with inappropriate and indigestible matter that will damage and weaken your body.
A crucial stumbling block in the ability of humans to comprehend information about themselves. Speciesism or homocentricity, call it what you will. Unfortunately from the beginning of our lives most of us are taught - both overtly and subliminally - to regard humans as something outside (and above) nature. This is called speciesism and it is as absurd and unpleasant as racism, sexism and all the other kinds of -ism. Speciesism provides the platform upon which we willingly accept all manner of dietary misinformation. Religious and political dogma reinforces the notion that humans are the pinnacle of all evolution. If humans are top of the pile then it follows that everything else is inferior. Can other animals speak, can they make intelligent decisions … are they able to use a computer? No!! Let’s chop them up, keep them in cages and eat their children. Perceived superiority is used by humans to justify all manner of barbarity. This is why slavery exists. This is why bullying, child abuse and other manifold inequalities are ubiquitous in most human societies. It is revealing that humans tend to refer to each other as “animals” only at the precise points when our behaviours are most crucially and unmistakably human.
We need to dispell the notion of evolution as a linear sequence. Mammals are not more evolved than insects. Primates are not more advanced than rodents. Humans are not at the top of some divine hierarchy. We are simply one of approximately 3 million different types of animal. Each of these is the unique outcome of millions of almost imperceptible genetic changes over successive generations. Each species has its own special features and predilections which distinguish it from all others. The singularities of the human species are immediately obvious. We are the only animals that routinely destroy and pollute our own environment on a massive scale. We are the only animal that imprisons and degrades other species. We are apparently the only animal that has convinced itself that our every action is sanctioned by divine will. Sadly these are the diagnostic features of the human species. Contrary to popular self-importance we do not hold exclusive rights to art, music, culture, society, play, education or altruism – these are all widely spread amongst other animals. But what of our huge brains, our empathy, our ability to solve crossword puzzles! Facile speciesist nonsense. Intelligence is not a reliable characteristic for defining a species or an individual. How could I dare to make a statement on the mental capacity of a non-human animal, when I cannot be certain that the other humans I can see in the street are capable of sentient thought. They seem to be mostly preoccupied with finding food, staying warm and securing future copulations. Their aims are broadly similar to those of the pigeons at their feet. I can only speculate as to what may be going through their minds, as I may also wonder at the thoughts of a dragonfly or how the world is experienced by a tree frog. Intelligence levels of non-humans cannot be quantified, therefore this concept is beyond the realm of scientific enquiry. Humans are better at being human than any other species, but we are not very good at being aardvarks or woodlice, and to imply that there is some kind of inherent entitlement or worthiness in just being a human is an example of speciesism.
Furthermore it is not really possible to differentiate between instinctive and learnt behaviour. Most humans are comfortable in the idea that their behaviour is a consequence of learning whilst other animals operate primarily by instinct. This is further unprovable, fallacious speciesism.
Dietary terminology, or What actually is an omnivore? If we reject the speciesist viewpoint we are able to learn a lot more about ourselves. We can look to other animals to reveal information about our place in the wider picture.
The terms omnivore, herbivore and carnivore are widely misused. To avoid further confusion - an omnivore is an animal that eats a range of food consisting of both plants and other animals; an herbivore is an animal that only eats plant matter; a carnivore only eats other animals, either capturing them itself or eating those that are already dead. There are other less frequently used diet-specific labels – frugivores, granivores, insectivores, nectivores, piscivores etc. Obviously these are not always strict categories. Most animals, except extreme dietary specialists, are omnivores to some degree. Large herbivores such as elephants and cows are bound to ingest small insects and other creatures amongst their plant food, and there are very few exclusive carnivores. Most animals will vary their diet opportunistically as new foods become available. This is a vital part of evolution. This is what ancestral humans did many thousands of years ago when they first started to scavenge dead animals.
The question now arises as to whether our bodies have had sufficient time to adapt physiologically to this new diet. This will form the main basis of the following discussion.
Humans are able to exist as omnivores or as herbivores. Despite popular claims a human cannot be a carnivore. This was discovered by large number of Canadian fur trappers last century. They attempted to survive by eating only the animals that they trapped, mostly Snowshoe hares. The most successful carnivore amongst them lasted less than 3 months.
Humans as a part of the class Animalia. Humans are classified as follows. We are animals, thus separate to plants, fungi or bacteria. We are vertebrates, thus allied to birds, reptiles, amphibians, fish and other mammals. Within the class Mammalia we belong to the order Primata, which also includes apes, monkeys, lemurs, lorises and tarsiers. (And if you don’t know what a tarsier is, do a quick image search because you really should be acquainted with these delightful little things).
The primates can be split into three broad groups :
1) The “primitive” prosimians (literally pre-monkeys) include lemurs, aye-ayes, bushbabies, lorises, pottos, angwantibos, and all manner of endearing bug-eyed creatures. They are often characterised as nocturnal insect-eaters, but there is a trend for the larger species to be both diurnal and herbivorous. (Note that the frequent use of the word primitive in relation to these creatures is an example of scientific speciesism. They are called primitive because they are less like humans than the “higher” primates, not because they have stopped evolving);
2) The tarsiers occupy a somewhat intermediate position. To our human perceptions they appear to be most similar to the first group yet the structure of their nostrils implies that we share a common ancestor;
3) “Higher” primates (no bonus points for spotting the implicit speciesist terminology) are the monkeys and the apes. Humans are one of 7 species of “great” ape. The word great distinguishes us from the gibbons or “lesser” apes. Gibbons are the brachiating South East Asian maniacs who appear to have found the key to eternal joy through swinging.
The Higher Primates. The primates are a relatively recently diversified group. This means that genetically speaking they are all fairly closely related. For example all primates are more similar to each other than two-toed sloths are to three-toed sloths. In fact primates are much more closely related to rats and rabbits, than for example, a rhino is to an elephant or a hedgehog is to porcupine.
Within the higher primates, humans belong to the family Hominidae, which also includes two species of chimpanzees, two of gorillas and two of orang utans. Our closest genetic relatives are the two species of chimp. We share 99.6% of our genes with chimps. We are much more closely related to chimps than they are to the other apes. The two species of gorilla are more genetically distinct from each other than humans are from chimps, even though there is much greater physical similarity. The explanation for this is a process called neoteny. Most animals have an immature, non-reproductive stage before the appearance of secondary sexual characteristics. In humans and other apes this is the condition prior to puberty. Neotenous animals are those which are able to reproduce whilst still in a physically immature state. The most famous example is the Axolotl – an amphibian that never grows out of its aquatic larval stage under natural conditions. Basically, humans are neotenous chimps. We retain several characteristics of baby apes throughout our lives – our unhairyness, our proportionally large heads and brains, and our capacity for playfulness, curiosity and learning. Basically humans are apes that do not grow up, or if feeling less magnanimous, humans are immature, weapon-fixated, bald chimps.
The ape family are known for highly complex social structure as well as remarkable systems of communication based on facial expressions, gestures and varied vocalisations. All species are able to make and use tools, to build nesting structures, to care for their extended families. The close relationship between humans and chimps is revealed by further traits that are not shared with the other apes. In terms of behaviour we are particularly close to one of the chimp species – Pan troglodytes, the so-called “common” chimpanzee, a name no longer appropriate for this critically endangered animal. Amongst the traits shared by humans and common chimps, but lacking in almost all other mammals are tribal warfare, murder, rape and pet-keeping (wild chimps are known to keep Tree hyraxes – look them up! – as pets). The other chimp is Pan paniscus - the Bonobo or Pygmy chimpanzee – again a strange choice of name, as it is no smaller than the other species. Bonobos seem to have opted out of a violent lifestyle, solving disputes and easing potential conflict primarily through sexual stimulation. Their permissive, promiscuous and - perhaps crucially - matriarchal societies are striking in their peaceful and co-operative non-aggression, especially when compared to those of humans and common chimpanzees.
The higher primates are with few exceptions herbivorous. The primitive ancestral condition seems to be insectivorous, with more recently evolved species favouring a vegetarian regime. Most species subsist on fruits, seeds, nuts and the softer and fleshier parts of a large variety of plants. A few species have become secondarily adapted to occasional meat-eating, notably baboons and common chimps. The meat eaten by these species is usually in the form of small soft-bodied animals – invertebrates and baby mammals and birds. Infrequently, larger mammals (wild pigs, small antelopes, colobus monkeys) are hunted and eaten usually by groups. Unlike in many humans, meat never accounts for more than a small portion of their diet. In the case of chimps it is uncertain as to how recently meat-eating behaviour was acquired. Amongst the other apes, some male Orang utans have been known to eat small animals, whereas Gorillas and Bonobos never willingly eat meat.
What about canine teeth and intestines?
We have seen that humans are members of a large group of mostly vegetarian mammals. Our closest relatives are primarily herbivorous, none at all partaking in a meat-heavy diet. Humans evolved from herbivorous apes, and meat-eating is a relatively recent adaptation. So what about the school biology lesson? If we are natural vegetarians why have we got canine teeth and why don’t we have four stomachs?
If you were to compare a human skull with that of another ape or a monkey, one of the most obvious features is how proportionally small human canine teeth are. Most other higher primates have canine teeth twice as long. If canine teeth are indicative of meat-eating then why do all these herbivorous monkeys have large canines? The reality is that canine teeth in primates, and some other animals, are not actually linked to diet. Humans have canine teeth because our earliest ancestors had them and they are sufficiently useful not to have been lost through evolutionary caprice. Simply watching a monkey or an ape reveals how canine teeth are used prominently to enhance facial expressions and gestures – a very significant means of communication in this group. Of course they are also used in feeding, but most species that possess them are strict vegetarians.
Perhaps less surprisingly our guts are also very similar to those of other herbivorous primates. What is more surprising is that our guts are basically similar to those found in the majority of the 5000 other species of mammal. The textbook example which compares us to a sheep and a dog is distorting the true picture with its crafty choice of examples. In respect of our guts at least, humans are typical mammals. Most mammals are herbivorous and possess the same basic gut conformation. Horses, elephants, fruit bats, rodents, pigs, hippos, kangaroos, rhinos, tapirs, manatees, sloths, rabbits and of course, monkeys and apes all have the basic mammalian gut design – large stomach followed by long, twisted intestines.
Dogs and sheep are actually atypical in their respective guts. Dogs belong to the order Carnivora – the true carnivores. This group includes most of the specialist meat-eating mammals, and they have evolved their own modified intestines. Sheep belong to the group of ruminants in the order Artiodactyla. These are the cellulose digesters and they need multiple stomachs to process their harsh fodder.
What our bodies can tell us…
Eyes
One of the commonest misconceptions regarding human diet is that the forward-facing position of our eyes reveals us to be hunters, like lions, leopards and weasels. This is one of the silliest pro-meat-eating arguments. The binocular vision of humans is far more developed than that of any hunting mammal. Humans and all higher primates have two eyes situated on the front of the face. This gives us two slightly different views of the same panorama. To gain a wider field of view we must turn our heads. Many other animals (both herbivores and carnivores) have eyes situated on the sides of their heads which enables a far greater field of view but makes it harder to gauge distance. The position of our eyes provides us with depth perception and is clearly an adaptation of an arboreal mammal given to making dangerous leaps. Those tree-dwellers were our ancestors and we have retained their binocular eye condition. To suggest that forward-facing eyes are an adaptation to hunting is to show staggering ignorance of basic evolutionary processes. If this was the case then why haven’t the eyes of gorillas migrated to the sides of their head? Why haven’t all those other binocular-eyed primates taken up hunting?
One delightful benefit of our herbivorous heritage is colour vision. Amongst mammals true colour vision is only found in certain plant-eaters, though it is widespread in birds, reptiles and insects. In diurnal primates, colour vision seems to have evolved in combination with fruit-eating – allowing us to determine whether or not fruit is ripe. Most other mammals - including all carnivores - see only a few muted colours or scales of grey.
Teeth
The fact that canine teeth are widespread amongst plant-eating primates has already been discussed. There are further examples from other herbivores. Some of the largest proportional canine teeth belong to various types of deer – musk deer, muntjacs and Chinese water deer. These herbivorous animals use their teeth in combat with each other.
Of course true carnivores do use their canines in the procurement of food - and it follows that their canines are rather larger and more impressive than ours. Examine your own teeth in a mirror. Your canines are the two slightly pointy ones bordering the four frontal incisors. You have an upper pair and a lower pair. Do you reckon you could throttle someone with those?
Next time you encounter a friendly cat have a look at those canines. Even in such a small carnivore those teeth clearly mean business. Now consider that an average adult human is heavier than a leopard. A leopard can use its canines to squeeze the life out of an animal three times bigger. If we were supposed to be using our canine teeth to assist us in the act of meat-eating then it follows that we should be bringing down prey appropriate to our size. Go and try it. Go and find a cow and rip its throat out with your canine teeth. Or you could try the other carnivore trick of using the canine teeth to sever the spinal cord. Go on, pick a cow and take it out with your teeth.
The whole canine-teeth-as-the-hallmark-of-a-meat-eater myth seems to be based on a fundamental error. Someone in the dim and distant past seems to have got canines confused with carnassials. The special teeth of carnivores are nothing to do with canines. All true meat-eaters (in the order Carnivora) are equipped with carnassial teeth. These are razor-sharp, shear-edged teeth situated in the sides of the mouth. If that friendly cat is still hanging around try to see its cheek teeth, and then compare them with your own. Rather different. The jaws of meat-eating animals are only able to move in an up and down, snapping motion. This allows the carnassials to work like scissors, slicing through tough meat. This action increases the surface area of the meat before it enters the intestinal tract, allowing for the most rapid digestion necessary for a potentially toxic meal. The cheek teeth of humans are nothing like carnassials. Feel them with your tongue, and ponder the fact that if a cat tried to do the same it would hurt itself. In place of sharp carnassials, we have flat-topped premolars (in front) and molars (behind). These provide a level, grinding surface for pulverising plant material to release the nutritious cell contents. In common with all herbivorous mammals except the ruminants (giraffes, cows and antelopes etc.) we cannot digest cellulose - the material that makes up plant cell walls. The vital stuff that we need to stay alive is contained within these cell walls but we must use physical means to break them open. So the plant-eating mammal has flat-crowned teeth and a jaw that can move in a side to side motion as well as up and down. This enables our teeth to work like a pestle and mortar crushing tougher plant material.
Stomach
This is the first internal organ of digestion. Food travels from the mouth through a tube called the oesophagus to the stomach which is a muscular bag filled with hydrochloric acid and protein-digesting enzymes. The function of your stomach is dictated by what you choose to eat. There is a fundamental difference between animal and plant food which often goes unappreciated. Uncooked plant food is still alive whilst we are eating it. The cells are in tact, they still contain all their vital enzymes and the processes of life are still happening inside. Meat on the other hand, is resolutely dead. As soon as an animal dies it starts to rot. This means that decomposing bacteria start to invade the dead body. The cells of the dead animal rupture and empty their contents. The life processes stop.
If flesh is your food then it needs to be eaten before it putrefies. Carnivores have mechanisms to stop the putrefying bacteria present in meat from poisoning their bodies. They have very strong stomach acid, which has the double effect of killing bacteria and other micro-organisms, and also commencing the break down of the complex proteins found in meat. Humans and other natural plant-eaters have gastric juices 20 times weaker. Our stomach acid is not strong enough either to kill invading bacteria or to adequately digest meat. Consequently, bacteria in meat often survive the stomach acid to proliferate and cause food-poisoning in the lower gut.
Our stomachs do contain protein digesting enzymes but they are ill equipped to deal with excessive meat consumption. Our main stomach enzyme is a member of the endopeptidase group called Pepsin. Its job is to digest proteins by breaking the large Amino acid chains into smaller chains. We do not produce sufficient amounts of this enzyme to deal with large amounts of high quality protein. Consequently meat will pass through the human stomach into the small intestine largely untroubled by digestive processes.
Another major misconception regarding mammalian digestion is that plant eating mammals are all furnished with multiple stomachs. As already mentioned the majority of mammals are herbivores and only a small number of these have chambered stomachs. These are the ruminants or the cud-chewers and they are specialised grass and leaf eaters like cows, antelopes, deer, goats and sheep. Inside their first stomach chamber are colonies of bacteria which are able to break down cellulose - the material that keeps the good stuff inside the plant cells. Ruminants swallow their food which is broken down in this chamber before being brought back to the mouth for a second spate of chewing (the cud). It can then be swallowed again and digested properly. Ruminants feed on large volumes of low-nutrient food such as grass and leaves. Humans and most other herbivores do not need chambered stomachs because we do not eat tough material like grass, but instead feed on highly nutritious softer food such as fruit and nuts.
Intestines
Again there are major differences between the intestines of a typical meat-eater and those of a typical herbivore, and guess which ones are similar to human intestines! This part of the gut consists of two continuous tubes - the small and large intestines. In the small intestine food is absorbed into the blood stream to be carried away to the places where it is needed for growth, repair and respiration. The large intestine is shorter with a wider diameter. This is where water is absorbed back into the body leaving behind solid waste which can then be expelled through the anus. In true meat-eaters these tubes are comparatively short. Meat enters the intestines from the stomach already well digested, and is rapidly passed through the intestines before it has a chance to putrefy. The nutrients from the meat are absorbed through the gut wall and the indigestible parts (bone, hide, hair etc.) are expelled from the body. This is in complete contrast to the system found in the guts of humans and other plant-eaters. We have long, convoluted intestines perfect for the slower break down of plant material. Most of our digestion takes place in the small intestine rather than the stomach. A cocktail of enzymes is added to the food. These are mostly carbohydrate-digesters such as amylase that only work in an alkaline environment. Protein needs to be digested in acidic conditions therefore any meat eaten by humans which has survived the stomach acid will also remain largely undigested as it passes through the small intestine. Food typically takes hours to travel through the twisted human guts. If meat is amongst the ingested food then it has plenty of time to sit rotting inside the intestines, poisoning the cells that it contacts. This is the main cause of colon cancer, a disease almost unheard of amongst herbivorous humans. These problems are compacted by other poor dietary choices. Often human diets that are rich in meat and other animal products are the lowest in fresh fibrous plant material. Fibre is needed to encourage the movement of food through the gut through a process called peristalsis. Heavy meat-eaters are facing the worst risk of cancer and other diseases caused by meat staying lodged in their digestive systems for days, in some cases years. If you are not expelling waste two or three times a day then you are not eating enough fibre. You really don’t want that stuff sitting around inside you for longer then is necessary.
The chemicals produced in our bodies also provide vital insight into the foods they are expecting to deal with. We have already discussed our weak Hydrochloric acid and our alkaline intestinal conditions. The substances we do or do not produce reveal much about our herbivorous nature.
Enzymes
They are the chemicals which break food down into smaller more digestible pieces. Many different enzymes are produced inside our bodies, each one specific for a certain type of food. Additional secondary enzymes, necessary for efficient digestion, are gained by eating fresh living plant material. The must abundant human enzyme is Amylase which is needed for starch breakdown. Starch is a long complex carbohydrate molecule composed of a string of numerous tiny molecules of glucose. We need the glucose for our most fundamental cellular processes – respiration! – and it can be most readily acquired from plant sources. Meat-eating animals do not produce Amylase, because starch is only found in plant-based food, therefore they must obtain their glucose secondarily from animal sources - an energetically expensive process.
Different enzymes are used to break down long protein chains into Amino acids which are also essential for basic bodily function. Meat is a complete protein containing all the essential Amino acids but it is not easily digested by the human body. Our protein digesting enzymes are much more effective at digesting rich plant sources such as beans and nuts. All the essential Amino acids are easily obtained from a variety of plant proteins.
Vitamin C
This is an essential nutrient for health and well being. Humans must consume small amounts of Vitamin C every day. Dietary Vitamin C is only available from plant sources. True carnivores make their own Vitamin C and are unable to process dietary Vitamin C. Cats and dogs have been fatally poisoned by accidental consumption of foods rich in Vitamin C.
An interesting aside illustrates that at least one group of humans are evolving towards a less herbivorous diet. The Inuit (formerly Eskimo) of high northerly latitudes traditionally lived in conditions where fresh plant material was unavailable for long periods of time. Alone amongst humans, but similar to true carnivores, the Inuit are able to synthesise their own Vitamin C when it is absent from their diet. However this should not be taken as an indication that human physiological evolution is moving towards a meat-rich diet. It is more an example of how extreme environmental conditions can favour rapid adaptive changes which enable a species to cope. The fact that the traditional Inuit diet is insufficient for a healthy human body is illustrated by the incidence of another diet-related disease. Osteoporosis is a condition caused by a lack of Calcium. This mineral is essential for healthy teeth and bones and needs to be taken in through food on a regular basis. It is found in a wide variety of both plant and animal food. However, Calcium deposition on human bones is negatively affected by the consumption of excessive animal protein in the diet. We are taught at school that milk is the best source of this element but in consuming animal products we are hampering our body’s ability to absorb Calcium. Osteoporosis is the condition arising when Calcium deposition is insufficient to maintain strong bones. By far the highest incidence of this disease (>50%) is amongst the Inuit people who also have the highest levels of meat and fish consumption.
The insides of our bodies reveal a lot about our natural condition. But our external appearance also suggests a creature poorly design for rapine and savagery. Humans have no natural weapons to catch prey. We have no claws, our teeth are ineffective, our eyesight and hearing are mediocre and our sense of smell is feeble. Even the fastest human could not outrun a meandering antelope.
Of course there are those fabulous brains we are always slapping ourselves on the backs about. Another common textbook diagram shows a graph of brain size to body mass ratios. Humans are sat there at the top looking down on our closest competitors – the chimps and bottle-nosed dolphins, and, oh look at the woeful sheep all the way down there. The sole purpose of this diagram seems to be the reinforcent of nonsensical speciesist contrivances. The careful choice of representative animals may imply to our human sensibilities that there is some kind of link between brain and body mass ratios and intelligence. But include a rat or a mouse on the diagram and it suddenly looks less comfortable for the sanctimonious primates.
Further absurdity. A popular pseudoscientific television programme went so far as to state that meat eating was the fuel for our brain enlargement and our consequent technological outpouring. Perhaps this show received funding from the meat industry, I do not know. In any case they failed to explain why the world is not full of laptop-proficient tigers and missile-wielding polar bears.
The reason we have no natural weapons are twofold. Our ancestors were plant-eaters, without the natural accoutrements for capturing prey. Therefore we could not have inherited them. Secondly meat-eating in humans has been a form of cultural, not biological evolution. There has simply not been enough time for the human body to change from a plant-eater to a meat-eater.
Think of the Giant panda, a true carnivore which has gone the other way, and become vegetarian. This is a much more ancient species than humans. There have been Giant pandas around for millions of years, and several important changes have allowed this creature to adopt a herbivorous condition despite its ancestors being meat-eaters. Yet still the panda is somewhat inept at being a herbivore. It is unable to digest much from its chosen plant food and has to eat for up to 20 hours of each day. This is after millions of years of evolution. The human dietary shift towards omnivory is only a few hundred generations old. There has simply not been enough time for our bodies to adapt.
If you still plan to eat meat, consider this…
Like those chimps that chose to eat meat, it should make up less than 1% of your diet. The type of meat that would be most suitable for your digestive system would come from tender easily digestible animals. You should try earthworms (remove the soil first) or grasshoppers. Sit by a pond and catch tadpoles and newts. Baby robins and other low nesting birds would make an easy snack. You could put up nest boxes to encourage a constant supply of youngsters in the summer months. Nests of baby mice would also be easily digestible in the human stomach and if you swallow them alive you could get that vital headstart against colon cancer.
