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 does not overly stress the digestive, detoxification, or elimination system. Thus the toxic burden is at a minimum. Thus the real question here might be: 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! But, deviating too far from our human species-appropriate diet causes chronic health conditions because we are feeding our body the “wrong” food composition – which is basically complex chemical composition that the organism has not evolved and adapted to process biochemically. 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:
Even in nutrition, nothing makes sense except in the light of evolution!
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!
To read the full list of suitable and not suitable foods for humans, visit this article.
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? Because humans left their original tropical habitat with the help of sophisticated cultural adaptations (including altering food sources through cooking) that prevented local adaptations 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 ancestors before agricultural activity introduced new foods and depended on locally available foods at that time. However, paleoanthropology is one of the most uncertain disciplines in biology and, thus, a highly controversial field. We have very little information on what our ancestors’ diet really consisted of.
Also, the paleolithic dietary concept is hardly backed up with biological traits and dietary adaptations related to foods, foraging, digestion, and metabolism. Because of this, the paleolithic diet can be considered a “survival diet” with fallback foods, like cooked tubers and meat, before agriculture came into the picture. 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 “The Paleo 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. Chimpanzees: Frugivore Diet
Another way to study the diet type of a species is by using comparative anatomy and physiology. Diet-related traits like digestion, teeth, hands, or dietary enzymes, 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 “wild” diet.
And to no surprise humans share many striking adaptations specific for frugivores with their primate family. Read about human dietary traits below or in our in-depth article here!
Chimpanzees are humans’ closest living relatives – and they are specialized ripe fruit-eaters found in tropical habitats. Humans also originated in the tropics and are still is 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 small amounts.
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:
Learn more about high-fruit diets for humans in our free guide here.
3. Human Instincts
Instincts are a natural intelligence innate to all living organisms, to either be attracted or repelled to a food. Thus, our instincts are an underrated tool to help us studying 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 a 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 or kale, 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.
What adaptations tell us about the human species-specific diet
Humans are certainly highly flexible in their diet because of our skills to manipulate foods by cooking and flavoring. However, like all other animals, we have been shaped through evolution and adapted to forage certain foods. This is why studying adaptations to foraging different food types is essential to determine our natural diet. However, in nutrition, this approach rarely gets even mentioned! Comparative dietary analysis in evolution and nutrition science is either the neglected stepchild or the ignored elephant in the room!
What are adaptations, and what can they tell us about the diet of a species – and the human species?
What is an adaptation?
What is an adaptation? Organisms constantly need to adapt to a changing environment. They do so on different levels and timelines:
- Within one individual: immediate response to environmental impacts on the epigenetic level. One and the same individual can look different under varying environments. This means its appearance and traits can vary for the same genotype – also called phenotypic plasticity. This plasticity is limited by the given genetic framework.
- Within a species: long-term evolutionary response to environmental conditions on the genetic level. Genetic changes only happen over generations within a species.
Adaptations for food and foraging
Species evolve under the selective pressure of their environment, including food availability: Individuals that are effective in foraging generally have better chances to survive, reproduce and pass on their genes (fitness). This can include finding food sources fastly, or effective digestion to get energy and nutrients or tolerating the toxic components in foods well.
Simple example: frugivorous primates have “handy” hands for fruit picking and holding. If you think this is too simple, you have never seen your dog trying to pick a berry from bushes with its snout (paws don’t serve at all) or chewing a piece of apple.
When is a biological trait adaptive?
- An adaptive trait is a characteristic of an organism that has evolved to be advantageous for its survival and reproduction.
- A trait is adaptive within a given environment if the animal is more successful with it than without it.
- Adaptive traits in one environment can be non-adaptive (useless or neutral) or even maladaptive (disadvantageous) in another environment.
Adaptations come at a cost
Adaptations to a challenging environment are costly or lead to constraints in other traits (energy expenses or trade-offs). And in nature, energy saving is key for being functional and successful. Energy that is saved by not sustaining one trait can be used for another, more advantageous trait. Thus, if a trait is not used, it can get lost (dysfunctional genes) over generations, which can be a benefit for the organism itself (see below the loss of vitamin C genes).
Adaptive traits help us understand our species-appropriate diet!
Because of our complex and widely unknown recent ancestral dietary past, comparing adaptive traits related to foods and foraging to other apes and primates is an important tool for more insight.
And surely, studying anatomical and physiological adaptations of frugivorous primates and primate foods in the wild reveals nothing short of surprises about ourselves and our special evolutionary relationship with fruits – as frugivores.
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 own 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.
In-depth article on these traits 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!
Conclusion
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. The take-away 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 a real-life perspective, 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.
There are some clear drawbacks in 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 important to the understanding of our natural habitat and diet. Thus, the comparative evolutionary analysis has many advantages in this sense and allows also 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.
Combining both approaches by studying the here and now, plus understanding human adaptations to colder climates and their more recent food sources (i.e. cooked food tolerance, fire smoke toxins and lactose tolerance) can be valuable when we do not have abundant access to the foods needed for a tropical frugivore diet! We then might have to consider integrating the best-possible fallback foods for each case into our diet!
Learn more about fruit diets here:
Go to How to do the Frugivore Diet
If you are new to this, visit this overview about frugivores and frugivory here!
References
- Paleolithic diet. Wikipedia (2023) (available at https://en.wikipedia.org/wiki/Paleolithic_diet). (link)
- D. J. Bergman, Fraud and forgery in paleoanthropology. Answers in Genesis (2009) (available at https://answersresearchjournal.org/fraud-and-forgery-in-paleoanthropology/). (link)
- R. Lewin, “Chain of Fraud” – Bones of contention (available at https://www2.clarku.edu/faculty/djoyce/piltdown/map_expose/chain_of_fraud.html). (1987) (link)
- H. A. M. Daanen, W. D. Van Marken Lichtenbelt, Human whole body cold adaptation. Temperature. 3, 104–118 (2016), doi:10.1080/23328940.2015.1135688. (link)
- K. Milton, Nutritional characteristics of wild primate foods: Do the diets of our closest living relatives have lessons for us? Nutrition. 15, 488–498 (1999), doi:10.1016/s0899-9007(99)00078-7. (link)
- Adaptation. Education (available at https://education.nationalgeographic.org/resource/adaptation/). (link)
- Y. Tu, W.-J. Rappel, Adaptation in living systems. Annual Review of Condensed Matter Physics. 9, 183–205 (2018), doi:10.1146/annurev-conmatphys-033117-054046. (link)
- N. Stewart, Smoke signals: DNA adaptation helped early humans deal with toxic fumes. The Guardian (2016) (available at https://www.theguardian.com/science/2016/aug/02/smoke-signals-dna-adaptation-helped-early-humans-deal-with-toxic-fumes). (link)
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