It is no secret that we, as modern humans, have extremely deviated from our natural diet. To the extent that we don’t know what the natural human diet looks like – the diet that is specific to our species in nature! The question “What diet have we evolved to eat?” is actually a pressing issue in today’s contradictory dietary jungle. Luckily, our anatomy and physiological adaptations to diet don’t lie and offer a reliable compass.
The species-specific diet and health
For every animal species in nature, we can observe a specific diet – the species-appropriate diet. We often forget that humans also have a species’ natural diet. What foods are “biologically appropriate” for us is based on the evolutionary concept that we have developed specializations and adaptations to forage and digest specific foods over time while others we cannot.
The species-specific diet is biologically best suitable for the human body – and, therefore, the healthiest diet there can be! The foods of the biologically appropriate diet provide the organism with the nutrition it needs and do not overly stress the digestive, detoxification, or elimination system. The toxic burden is at a minimum. Considering these benefits, a valid question arises: Why is studying the evolutionary diet of humans not gaining more attention in nutritional science?
Most of us eat foods all day long that are not suitable for humans! However, deviating too far from our human species-appropriate diet causes chronic health conditions because we are feeding our body the “wrong” food composition. Foods are basically a highly complex “chemical mixture” that the organism has to process to extract nutrition and excrete what is not needed. Depending on the food sources of our ancestors, we are more or less well adapted to biochemically process a particular food.
Species-specific diets are well-known to anyone who feeds or observes animals, like animal caretakers, biologists, or pet owners. Wrong feeding causes disease in animals… and humans. Dobzhansky’s famous “Nothing in Biology Makes Sense Except in the Light of Evolution” includes foods and nutrition:
It seems, however, that we have forgotten about this natural principle for our own species, due to cultural reasons. We even seem to have forgotten what our own species’ diet is. It’s essential, however, to re-discover what is supposed to be in our instincts: learn what we should eat naturally by understanding foods and learning from our closest relatives, the chimpanzees!
How can we study the human evolutionary diet?
Determining the specific-specific (or biologically appropriate) diet of humans is more complicated than in other species. Why? Humans left their original tropical habitat, tropical forests, with the help of sophisticated cultural adaptations, including altering food sources through cooking. Those skills prevented evolutionary adaptations to a new environment and foods to a large extent.
There are two approaches to investigating our evolutionary diet. One is studying hunting-gathering humans before agriculture, and one is comparing humans to our closest living relatives, the chimpanzees, and their diet – which is a frugivorous diet!
1. Hunter-gatherers: Paleolithic Diet
The most popular evolutionary diet is the paleolithic diet, or “a hunter-gatherer” diet. This basically means studying the diet of our direct and recent ancestors before agricultural activity introduced new foods and depended on locally available foods at that time.
There are two major issues with the hunter-gatherer diet: firstly, paleoanthropology is one of the most uncertain disciplines in biology and, thus, a highly controversial field. Secondly, the hunter-gatherer is a survival diet. It is not the diet we have evolved to eat. Human ancestors evolved in tropical forests with a diet based on fruits. Basically, hunting was the survival strategy outside our natural habitat – and meat and cooked foods were (and still are) our fallback foods. We adapted mainly by using tools and fire.
This is the reason why the paleolithic dietary concept is hardly backed up with biological traits and dietary adaptations related to foods, foraging, digestion, and metabolism. For example, humans have not evolved with a cooked diet; we have only adapted with a slightly higher tolerance towards cooked foods, with a decreased immune response, but cooked foods still trigger our immune system, unlike raw foods. We are thus not “cookivores” that are hooked to a cooked diet. Read more about cooked foods and our earliest ancestors’ diet here.
The modern interpretation of a paleolithic diet is basically omnivorous, including (cooked and raw) vegetables, fruits, greens, meat, eggs, nuts, and seeds. The diet often does have significant health benefits, as it is a significant improvement on an average diet. Leaving out grains and processed foods is a huge step towards better health, but is it really the ultimate evolutionary diet?
2. Apes: Frugivore Diet
Another way to study the diet type of a species is by using comparative anatomy and physiology – comparing adaptations related to diet. Diet- and foraging-related traits like digestion, teeth, hands, taste receptors, or biochemical characteristics are compared to closely related species, in our case, primates. In anatomy, the function of a structure or a trait can be predicted by its form. Thus, shared traits in evolution indicate similar dietary ecology. And because we can observe the diets of those species in the wild, we can learn about our own natural diet.
Humans share many striking adaptations specific for frugivores with their primate family, especially apes, which are all highly frugivorous.
Chimpanzees are humans’ closest living relatives – and they are specialized ripe fruit-eaters found in tropical habitats. Humans also originated in the tropics and is still a tropical species (Daanen et al., 2016).
So what’s the Chimpanzees’ diet like?
Chimpanzees mainly eat tropical fruits (around 70%), but also greens, nuts, bark, flowers, and some animal foods like insects, eggs, and sometimes meat. So, frugivores mainly forage for fruits, but they do consume other food types in much smaller amounts.
Adaptations in humans that are typical for frugivorous primates
What traits specialize frugivores in a high-fruit species and diet? Humans and Chimpanzees share intriguing features with each other that serve essential functions in fruit foraging. They also share many features with other frugivorous mammals, which are not as closely related. The same diet can lead to the same adaptations in species of different evolutionary lineages independently (analogous traits).
List of some of the most remarkable biological features that have evolved with our dietary habits as highly frugivorous species:
- Loss of internal vitamin C synthesis due to high fruit intake, a characteristic specific for frugivorous animals.
- Trichromatic color-vision: specialized color-vision for highly effective fruit foraging.
- Digestive anatomy and microbiome like other frugivorous primates.
- Dentition typical for frugivorous primates
- Complex hand with opposable thumbs needed for tree life and fruit foraging.
- Tasting sweetness. While we love sweet – not all animals can even taste it!
- Instincts: sensory cues strongly attract us to ripe fruits (color, smell, taste), unlike any other food in nature.
- Humans originated in the tropics: tropical forests are the only habitat that sustains larger frugivores.
A major difference of the primate frugivorous diet compared to the Paleolithic dietary concept is not only the much smaller proportion of meat, but also that there is no cooking! Everything is raw – straight from nature. Here is where instinctual knowledge becomes a thing:
3. Human Instincts
Instincts are a natural intelligence innate to all living organisms, to either be attracted to, or repelled by a specific food. Thus, our instincts are an underrated tool to help us study our species-appropriate diet: Natural dietary behavior (i.e., in children) or our own taste receptors, and visual and olfactory cues can give us important information on what we would actually eat.
Simple questions related to our own instincts and behaviors can aid to identify the human species-appropriate diet: in what environment could humans live without infrastructure and food processing? In other words: to what conditions are we adapted biologically? What foods can we eat straight from nature? Animals obviously know what to eat in the wild by using their instincts. Try feeding an impala fresh meat and a lion fruits…
Grains are an example of what we eat today that is not really human food: Grains are not something we would consider food in the wild! It does not look or taste appealing. Most grains need to be processed and cooked to be edible! Grain-eaters (granivores) like insects and birds are adapted to grains and their toxic defense chemicals plants release to protect their progeny. We are not. Now, we call them “anti-nutrients“.
We can ask these questions about any other food: For example, would we eat raw meat straight from nature? And would we find it appealing? Or rather see this as a “second choice” type of food? Would we eat beans, roots, kale, or insects? Some foods would not be our preferred food, but they serve as fallback food. But some foods we eat today are highly toxic when raw! Read more on suitable food groups for humans here.
Aren’t humans clearly classified as omnivores?
Yes, humans are classified as omnivores because we are able to digest both, plants and animal-based foods.
However, humans do have distinct adaptations as specialized fruit-eaters like our closest living relatives, all great apes, and many other frugivorous primates, which are classified as frugivorous omnivores. Therefore it would be worth a discussion to specify the human dietary classification and refer to humans as frugivorous omnivores, too. What might seem like detail is essential in shaping the perception of our natural diet!
Should we be learning from chimpanzees or hunter-gatherers?
This question does not have a clear-cut answer because we do not live in our natural environment. We might should be learning from both! The takeaway message is that humans share a lot of adaptations and instincts with chimpanzees in terms of diet, which should no longer be ignored. A diet high in tropical fruits seems a good idea, in either case!
From real-life experience, both diets can improve health, as many inflammatory foods are left out in both of them! However, there are levels to health, and the health-improvement reports of people going on the frugivore diet seem to far outperform the paleo experience. However, a frugivore diet demands that we live in a tropical, natural environment in the long run!
There are some apparent drawbacks to studying the paleolithic diet! While studying our direct ancestors is fascinating, it is clearly limited, as we look into a widely unknown past. Also, the paleolithic diet does not take into account that cultural adaptation does not equal biological adaptation, which is essential to the understanding of our natural habitat and diet. Thus, comparative evolutionary analysis has many advantages in this sense and also allows for real-life observations and experiments.
Adaptive traits in anatomy and physiology related to diet, reveal the dietary ecology of a species – including humans. Thus, by studying our characteristics for foraging we can discover a lot about the natural human diet.
We find that humans share many fascinating traits with their closely related frugivorous (fruit-eating) ape and primate family. Comparing the diets and traits of wild chimpanzees certainly deserves more attention when studying the species-appropriate nutrition of humans.
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