Human Origins, Diet & Lifestyle
This is a story about humans—where we came from, and what diet and lifestyle we followed along the way.
This will help us triangulate what to eat and how to live today.
Prologue
Koalas don’t need dieticians, so why do we?
Per evolutionary theory, animals are adapted to their historical environment, diet and lifestyle.
For a koala, this means spending most of their time climbing around (or sleeping) in eucalyptus trees. Eucalyptus leaves are their primary food source.
Image: Unsplash
Observe that the physical attributes of koalas are perfectly designed for this way of life. For example, their sharp claws, strong arms and legs make them excellent climbers, who can comfortably live amongst the trees.
Their digestive systems are also specialised for the task of digesting eucalyptus leaves, which are highly-fibrous, low in nutrients, and contain a vast array of (toxic) plant defence chemicals.
Koala digestive anatomy. Koalas, like all animals that consume significant amounts of fibrous plant foods, have very distinctive digestive features, such as a complex large intestine (where trillions of microbes digest the cellulose and turn it into usable energy).
Image: Stevens & Hume (1998)
In summary, koala anatomy and physiology is perfectly suited to their instinctive behaviours—climbing around / sleeping in eucalyptus trees, and consuming large amounts of eucalyptus leaves.
Examining human evolution, behaviour, anatomy and physiology offers similar clues that can help us rediscover our true dietary preferences and nutritional needs (discussed in detail further below).
Consequences of unnatural diet & lifestyle
What happens when we remove koalas (or humans) from their natural habitat, and feed them artificial diets?
Animals living in captivity, such as the lion cubs at the London Zoo in 1889 (who had been removed from their historical environment, and fed inappropriate diets) become malnourished, suffer various symptoms of ill health, and eventually develop chronic diseases.
This is also what we see in modern human civilisations—unprecedented rates of malnutrition, disability and chronic diseases (often called ‘syndromes’).
Considering the scientific and technological progress that modern humans have made elsewhere, it’s almost hard to believe how badly we’re faring with chronic diseases (especially prevalent since the industrial revolution).
Missing the forest for the trees
There are two major problems with modern science;
Bias, conflicts of interest, corruption, and political / corporate interference. These influences (along with non-replication and methodological errors) are so pervasive in modern science that Ioannidis stated in 2005 that the majority of published research findings are false. The implications of this are huge.
Fragmentation of scientific disciplines, over-specialisation, and echo chambers. Biological systems do not operate inside vacuums; everything is inter-connected and inter-dependent. In other words, specialisation, while helpful, also comes at a cost. Why do we so often fail to address this fundamental principle when studying / teaching / prescribing?
Regardless of such reasons, at the end of the day, the public health and nutrition science apparatus informs the dietary guidelines.
Official guidelines have the potential to build individual and generational health. By the same token, they also have the potential to destroy it.
So, if our dietary guidelines are erroneous (and they are), this is a monumental problem—a knot that will take generations to undo.
We no longer know what to eat (unlike koalas)
Traditional dietary habits and human instincts have been replaced by marketing, memes, and social conditioning.
Nutritional inadequacies, and deficiencies are now the norm.
Disability, ‘syndromes’ and chronic diseases are at unprecedented levels.
Fecundity / reproductive health (a good way to measure our species’ overall health) has declined precipitously.
These are not good signs for any organism.
The worst part is that we know our dietary choices are a major driver of this problem.
Junk food / drink is a known cause of ill-health. Consumption of ultra-processed food and drinks is continuing to increase. These products are highly-profitable, addictive, contain toxic ingredients, and are unethically-marketed to young children.
Image: Unpslash
The modern human diet and lifestyle is at odds with our biological needs and expectations.
These recently-acquired behaviours are the root cause of most (recently-acquired) chronic diseases.
Modern nutrition ‘science’ has failed to produce more appropriate diets than those that our (much healthier) ‘primitive’ ancestors consumed.
The last remaining hunter-gatherer tribes (Hadza, Masaii etc., see further below) are real life examples of this—they do not follow Western nutrition guidelines, yet remain much healthier, and are considered an invaluable reference point for understanding default human health and behaviours.
The first step on the path to understanding human nutrition is to learn about nature, and our place within it.
This requires us to go beyond the treacherous, narrow-minded worldview of mainstream nutrition, to consider evidence from a range of (inter-dependent) disciplines; biology, zoology, anthropology, archaeology, primatology, anatomy and so on.
Here we go.
Tree of Life
The first terrestrial animals appeared over 500 million years ago (Mya).
Tree of Life—Animal Kingdom. Humans are a tiny speck, see bottom right.
Image: evogeneao
Ancient human ancestors
Humans are mammals—who arose ~200 Mya.
Among mammals, humans belong in the order of primates, who arose 50-80 Mya.
Primate Evolutionary Tree. Primates are mostly omnivorous, pro-social animals who typically live in, and around, the trees of tropical forests.
Image: Eat Ancestral
Recent human ancestors
Approximately 12 Mya, we split off from orangutans.
Approximately 10 Mya, we split off from gorillas.
Approximately 7 Mya, early humans and chimpanzees are the same animal, then we too diverge—the first chimpanzees, and the first hominins (human-like animals) arise.
Great Ape divergence over the past ~12 million years.
Image: Encyclopaedia Britannica
This is where the story of human evolution gets particularly interesting.
Up until this point (~5 Mya), we were very similar to modern-day chimpanzees—another quadrupedal, mostly plant-based primate, with an appropriately-sized primate brain (approximately 400-500 grams).
Big changes were afoot, however.
The first humans (genus homo) emerged ~3 Mya from the Australopithecina lineage.
Image: Wikipedia
Over the next few million years, our dietary habits would change, our brains would triple in size, and our bodies would transform into our upright, bipedal, modern-day human form.
Artist impression of the human lineage. How did we evolve from tree-dwelling apes into walking, talking humans? This is the big question.
Image: Encyclopaedia Britannica
Without a series of key evolutionary developments, we’d likely still be hanging in, and around, the trees of tropical forests in East Africa.
It is hard to overstate the gravity of these changes, which laid the foundations for modern humans…
Becoming self-aware
Developing tools
Controlling fire
Discovering food technologies (cooking / fermentation)
Creating art / music / languages
Discovering agriculture / animal husbandry
Inventing the wheel
Building industrial machines
Creating the internet
Effectively, without this series of events, we wouldn’t be having this conversation.
From primitive ape to modern human; key evolutionary developments
What follows is a very high-level view of key developments that have taken place since the time Australopiths arrived on the scene, roughly 5 Mya.
We transitioned to living permanently on the ground.
This created changes in our movement patterns and food supply.
We developed tools and weapons (clubs and primitive spears), and over time, became very effective hunters.
Adaptations to the hands, and the upper body (especially the shoulder) helped us become excellent at throwing projectiles (affording us the unique ability to kill from a distance)
Adaptations to the cardiovascular system (and other systems) increased our endurance capabilities
We followed this hunter-gatherer diet / lifestyle for millions of years, right up until the dawn of agriculture (~10,000 BCE).
Human anatomy and physiology adapted to these behaviours; especially hunting, meat-eating, and eating cooked foods.
Notable adaptations related to dietary changes…
Digestive anatomy and function evolved significantly.
Humans evolved from quadrupedal, plant-based apes, into bipedal, animal-based hunters.
Modern human anatomy and physiology (particularly digestive anatomy) appears largely the same as our recent ancestor Homo Erectus (now extinct), who arrived on the scene ~2 Mya.
H. Erectus is known for hunting megafauna (imagine animals 3-4 times the size of a modern-day elephant), and mostly consumed high-fat animal foods (estimates suggest >70% of their diet was animal foods).
This indicates the dietary specialisation of the human species has diverged significantly from the time of (mostly plant-based) Australopiths (~5 Mya.).
Unlike gorillas and chimpanzees, humans are adapted to obtaining the majority of our energy and nutrients from hunting, not foraging.
The term ‘omnivore’ is a source of great confusion
Humans are omnivores, but like most omnivores, we are highly-specialised (as opposed to being diet generalists, who are less fussy about their food choices).
We are specialised to consume fat and protein-rich foods (meat), and the least toxic, most digestible plant foods (fruit). We are not well-suited to digesting significant amounts of fibrous plant foods (leaves etc.).
Our ‘Sister Species’, chimpanzees, are a good example of the opposite specialisation—they are omnivorous, consuming ~10% animal foods, ~90% plant foods. Their digestive anatomy reflects these behaviours (see Gallery below).
So, humans, being omnivores, can eat a certain amount of plant foods, but this is no longer our primary food source (except during times of famine). Our primary food source, since the at least the time of H. Erectus (~2 Mya.) has been meat, fat and organs from hunted animals.
Considering how long we have been eating this way (99% of human evolutionary history), humans have become dependent upon animal-source foods (and the unique nutrients they contain) for optimal health. This is why we see nutrient inadequacies and deficiencies in people who do not eat, or have access to animal foods (vegetarians, people in developing countries).
See the below Gallery for further context, or skip to the bottom for a summary.
Gallery
Adaptations to ground-living
Tree-climbing vs ground-living anatomy. Unlike chimpanzees, modern humans are no longer proficient tree-climbers, but we are extremely well-adapted to walking, and running, long distances.
Image: Encyclopaedia Britannica.
Gorilla resting in a deep squat. While gorillas also spend time on the ground, their anatomy is clearly adapted for life amongst the trees. Note their grasping feet, similar to chimpanzees.
Image: Unsplash
Chimpanzees are knuckle-walkers. Chimps also spend time on the ground, however they are clearly specialised for arboreal activities.
Image: Unsplash
Chimpanzee (left) and human (right) hands are specialised for different tasks. Chimpanzees require larger, stronger hands for climbing. Humans, meanwhile, adapted smaller hands, capable of manipulating objects with precision.
Image: Young (2003)
Evolution of the human hand — power vs precision grip.
Image: Encyclopedia Britannica
Energy needs of large, hungry brains
Compared to almost all other animals, humans have very large brains (as a percentage of body size).
This is interesting, because large brains are expensive to maintain.
The brain is a very energetically-expensive organ. Despite only weighing ~2% of our total body weight, the brain takes up ~25% of our Total Daily Energy Expenditures (TDEE).
Image: Unsplash
If an organism ‘wants’ to evolve a bigger brain, that organism must secure access to the necessary resources (calories, growth factors, micronutrients…) for growth and long-term maintenance.
From where did Australopiths and early humans obtain the resources that allowed for the brain to evolve so quickly—to triple in size—over such a short period of time?
Brain size in primates was relatively similar (~350 cc) for tens of millions of years. Within a relatively short period (~5 million years), human brain size tripled, peaking at ~1600 cc. This is 3-4 times larger than that of our closest living relatives—gorillas and chimpanzees. As diet quality is tightly correlated with brain size, it appears that the significant increase in diet quality played a key role in this expansion.
Image: Encyclopaedia Britannica.
Time at the dinner table. Our closest-living relatives, chimpanzees, spend many hours per day eating in order to obtain their baseline energy and nutrient requirements. By contrast, humans can obtain their daily energy and nutrient needs in very little time at all. Differences in diet quality explain this conundrum.
Image: Unsplash
Chimpanzees, like most primates, consume a variety of fibre-rich plant foods, such as wild fruits, barks, stems, leaves and seeds.
These animals rely on microbial fermentation (in the large intestine) to turn this plant matter into usable energy—short chain fatty acids (SCFAs)—which is then absorbed across the gut wall and utilised to fuel metabolic demands.
However, the entire process is rather slow, and yields low amounts of both energy and nutrients.
Leaves are low in energy and nutrients. Leaves are highly-fibrous plant foods that yield low amounts of energy (calories) and nutrients (fats, protein, vitamins, minerals etc.). Note that plant seeds (incl. nuts, legumes, beans) and ‘vegetables’ (leaves, stems, roots) also contain anti-nutritional factors (tannins, phytates, oxalates, saponins etc.) that inhibit digestion, limit nutrient absorption, and burden organ systems (i.e. liver, kidneys) responsible for detoxification.
Image: Unsplash
A side-by-side comparison shows that, when compared to plant foods (especially fibrous ones) animal foods yield significantly more energy and nutrients.
Energy yield by macronutrient group. Pound-for-pound, fibrous plant foods contain / yield far less energy than fat and protein-rich animal foods. In this sense, simple sugars and (cooked) starches are also far more valuable than fibrous plant foods. Presence of anti-nutritional factors in plant foods further limits their energy/nutrient yield.
Image: Eat Ancestral
Net energy return of hunting vs foraging. When compared to foraging for plant foods, hunting produces more energy / calories per hour of work. Hunting large game animals is estimated to deliver a 10-30x greater return, when compared to (best-case) ripe fruits and (cooked) starchy ‘vegetables’. Remember that, aside from greater energetic return, animal foods are also far richer in bioavailable micronutrients.
Image: Eat Ancestral
Through hunting, humans discovered the most efficient way to obtain high-quality foods.
The highest quality foods found in nature—animal fat and protein—became the foundation of the human diet.
Humans (like chimpanzees) also value the highest quality sources of carbohydrates—simple sugars, from ripe fruit, and honey (later, when we learned to cook, this would include starch from cooked tubers).
There is a very strong case that these dietary shifts played a central role in human evolution, particularly with regards to brain and gut size / function.
Proposed evolutionary interplay between brain size, gut size and diet quality.
Image: Aiello & Wheeler (1995)
Access to high-quality animal foods (along with energetic savings from reductions in gut size, discussed below) would have provided the bulk of the necessary resources to fuel and sustain the expansion in brain size.
Evolution of human brain size over time. Coincidental, or instrumental?
Image: Saladino (2020)
Evolution of the human digestive system (the gut)
There is a strong inverse correlation between diet quality and gut size.
In other words, as diet quality increases, gut size decreases.
The human gut is 60% smaller than expected for similarly-sized primates. Humans do not possess the large, complex gut structures that are necessary for the digestion of significant amounts of fibrous plant foods, and subsequent nutrient extraction. Notice the flared-out ribcages of Chimpanzees and Australopiths, which allow room for long, bulky digestive systems.
Image: Aiello & Wheeler (1995)
Sheep (herbivore) vs dog (carnivore) digestive anatomy. Herbivores, such as sheep, who consume large amounts of (low-quality) fibrous plant foods require large guts for digestion and nutrient extraction. Carnivores, such as dogs, who almost exclusively consume protein and fat-rich animal foods, have simpler, smaller guts.
Image: Stevens & Hume (1998)
Let’s now compare humans and chimpanzees.
Gut structure is a reliable indicator of dietary specialisation. Humans and chimpanzees are both omnivorous, but like most terrestrial mammals, are highly-specialised (in opposite directions). Note the relative size and structural differences between the small / large intestines, especially the presence of a voluminous caecum in chimpanzees.
Image: Hunt (2020)
Chimpanzees have larger, more complex colons / large intestines (where fibrous plant matter is digested by microbes—see table below).
Humans, by contrast, have smaller colons, but larger small intestines (where fat, protein and simple sugars are digested—see table below).
Humans also have a highly-acidic stomach, pH ~ 1.5 (more acidic than most carnivores) which is essential for digesting protein-rich foods.
All together, this indicates our dietary specialisation—unlike most primates, humans are adapted to a diet mostly consisting of animal foods.
Digestion sites of macronutrients.
Image: Hunt (2020)
Humans’ ability to derive nutrition from fibrous plant foods is very limited.
As we have seen, the modern human digestive system is specialised to digest and absorb proteins, fats and sugars. Our ability to derive energy and nutrients from fibre-rich foods is very limited.
Our physiological limit—the maximum amount of calories—that humans can acquire per day from fibre fermentation (done by microbes in the large intestine) is estimated to be less than 10% of TDEE. Ten percent of the average human TDEE (2000 kcal) is just 200 calories.
Humans simply cannot be fibre-fuelled, unlike sheep, cows, gorillas and chimpanzees.
Gallery Recap
Humans are descendants of primates, who are largely omnivorous, and specialised to consume plant foods.
However, humans have evolved to specialise in hunting and consuming animal foods—this is our primary food source (and has been for at least 2 million years).
Humans retain the ability to consume some plant foods, but we are not well-suited for plant-based diets.
With specialisation comes dependency
The human species has a clear need for animal-source foods, and we should be eating far more of them than what modern nutrition guidelines suggest.
The only remaining question is, how much?
As noted earlier, meat-eating in humans is thought to have peaked during the time of H. Erectus, who arrived on the scene ~2 Mya, and lived for ~1.2 million years.
“H. erectus was morphologically and behaviorally adapted to carnivory, was a social hunter of megafauna, possibly specializing in large prey, which, by zoological analogy, would have been a hypercarnivore with some 70% of the diet derived from animals.”
Other researchers suggest that Neanderthals (homo neanderthalensis—another very close relative of ours) who also prioritised hunting large herbivores, were possibly even more carnivorous than H. Erectus.
As time went on, modern humans (homo sapiens) became more diverse in their approach (probably not by choice, but out of necessity due to megafauna decline) incorporating smaller game, and aquatic animal foods into their diets.
It is not until the dawn of agriculture that we begin to see the gradual displacement of animal foods with cheaper, nutrient-poor substitutes, such as grains, beans, and ‘vegetables’.
Modern humans are descended from a long lineage of hunter-gatherers
For millions of years, humans lived an active, outdoor lifestyle.
We ‘exercised’ every day, got plenty of sunlight, and were exposed to trillions of microorganisms (probiotics) living in the soil beneath our shoeless feet.
Since the time we evolved into humans the foundation of our diet has always been animal foods (meat, fat & organs).
Our secondary food sources are simple carbohydrates from fruit and honey. When humans learned to cook, starchy tubers also became a relatively high-quality option.
Highly-fibrous, nutritionally-poor plant leaves, stems and seeds were only eaten as fallback foods—when our primary and secondary food sources were unavailable (failed hunts, times of famine).
Even then, to render these plant foods less poisonous and more digestible / nutritious, we learned to employ various food technologies, such as soaking / leaching, fermentation, and cooking. Modern humans do not fare well on raw food diets.
As we have seen, our long-standing feeding behaviours / food preferences are clearly reflected in our anatomy and physiology.
These food preferences also persist among the last hunter-gatherer human cultures that have survived into the modern era.
Diets of modern-day hunter-gatherers
Hadza hunters. The preferred foods of the Hadza, who inhabit modern-day Tanzania, are honey, meat and fruit.
Image: Brian Wood
Inuit couple. In 1928, the arctic explorer Vilhjalmur Stefansson wrote: “the chief occasion for vegetables… with most Eskimos, was famine.”
Image: Frits Johansen
Maasai warriors. The nomadic, pastoralist Maasai, who inhabit modern-day Kenya / Tanzania, live off a steady diet of milk, blood and meat.
Image: José Valero
These ‘primitive’ humans continue living their ancestral lifestyle, care little for Western nutrition ‘science’, and interestingly, do not suffer from malnutrition and chronic diseases like ‘civilised’ people do.
One might suppose that they are healthy because they are satisfying their biological needs and expectations—behaving like humans have always done—by consuming nutrient-rich foods, spending lots of time outdoors; getting adequate sunlight and regular exposure to microorganisms, among other things.
Contrast this with the modern (post-agricultural / industrial revolution) diet and lifestyle of humans;
Largely sedentary, indoor populations
Nutritionally-inadequate, plant-based diets; rich in grains, plant fats (like seed oils), and ‘vegetables’
Public health authorities recommend that we avoid the sun, and frequently sterilise our bodies and homes, for fear of ‘germs’
Regularly exposed to novel chemicals, food additives, plastics and other agents of environmental pollution.
Humans are not well-adapted to these modern behaviours, and we are paying an enormous price; infertility, diabetes, cancer, heart disease, Alzheimer’s, depression, anxiety, and so on.
These preventable conditions—these diseases of lifestyle—are responsible for causing the majority of global deaths, and represent the sinkhole into which the majority of public healthcare budgets are disappearing.
Our suffering is largely caused by our historical and nutritional ignorance.
Practical take-aways
Humans are hunters first, gatherers second.
We have been purposefully consuming significant quantities of animal foods for at least 2 million years, probably much longer.
Human anatomy is specialised for the task of hunting, eating and digesting protein and fat-rich foods (meat, animal fat), plus simple sugars (honey, fruit).
Human physiology is critically dependent upon the unique nutrients that animal foods provide (such as; essential amino acids, fatty acids, bioavailable vitamins and minerals) to ensure optimal growth, development, learning, and lifelong wellbeing.
Modern humans develop predicatable nutrient deficiencies when eating plant-based diets. Studying human evolution, anatomy, physiology, and traditional human diets explains why.
This also helps us understand why removing plant foods from the diet is a key part of highly-successful protocols aimed at reversing gut and autoimmune-related diseases. When stressors are removed from the system (and homeostasis is achieved) the body can often heal itself, and return to it’s natural state—of health.
Epilogue
It is my sincere hope that this has provided some clarity about who we are, where we come from, and how we should consider eating / living today.
In the modern era, eating meat and animal fat is seen as unhealthy, unethical, and a major cause of environmental destruction.
It should be obvious to the reader that the nutritional claim has no basis in fact, and that the opposite is actually true.
We should thus be very skeptical of any related narratives, which (well-intentioned or not) may also end up causing more harm than good.
Note: it is outside of the scope of this article, but I believe that proponents of plant-based diets are largely wrong on all three accounts (nutritional, ethical and environmental).
Our default state is health, not disease (unlike the current state of public ‘health’).
Following in our ancestors’ footsteps (in terms of diet and lifestyle) is the quickest, cheapest way out of this mess.
And no, one does not need to go live in the bush like a hunter-gatherer to experience the benefits (although frequent nature excursions are highly-encouraged).