What have we evolved to eat? This is the fundamental question when taking a biological view on nutrition – and there is certainly room for more input and debate. Humans undoubtedly come from a highly frugivorous ancestry. And the majority of primates, including chimpanzees, are still frugivores today! Humans share many traits related to diet and foraging with frugivorous primates, which is why we appear to be specialized fruit-eaters, too. The undeniable resemblance raises the question: Are humans frugivores?
Adaptations indicate that the human evolutionary diet is highly frugivorous. We have culturally developed cooked omnivorous diets, but humans are still biological frugivores!
If you are convinced that nature doesn’t lie, then the frugivorous characteristics of humans will surprise you:
If you are new to this, visit this overview about frugivores here!
1. Frugivores have lost their Vitamin C-Genes – including humans.
An unequivocal biochemical feature that has evolved in humans due to fruit-eating is the loss of vitamin C-synthesization. This is a unique trait shared by highly frugivorous animals. Most mammalian species do produce Vitamin C themselves, includes meat-eating species like dogs, cats, but also herbivores like cows, which all have functional vitamin C genes.
The vitamin C loss mutation (Jukes & King, 1975) has occurred analogously in highly-frugivorous birds, bats, guinea pigs, and apes (including humans). The high intake of Vitamin C from fruits made internal vitamin C production non-vital (Drouin et al., 2011).
The evolutionary pattern shows that within a closely related group (“phylogenetic clade”), only the fruit-eating species have lost their functional vitamin C genes. While non-frugivorous species have kept their internal vitamin C production. This makes the “lost vitamin C genes” a trait that seems to evolve analogously due to high fruit intake.
This phylogenetic tree by Drouin et al. (2011) illustrates the ability of different mammals to produce vitamin C. Dark green species produce vitamin C, light green species don’t produce vitamin C.
All apes (including humans) and most primates need to consume vitamin C from external sources (fruits). However, lemures are an exception in the primate family: Lemures still produce vitamin C themselves – and to no surprise, lemures “consume much fewer fruits than other primates,” as elaborated by Jason G. Goldman in this Scientific American article. Read the whole article on vitamin C and frugivores here.
2. Trichromatic color-vision is a trait specific to frugivores.
Most frugivores, including humans, see more colors than other species – we have trichromacy. This color-vision characteristic is optimized for detecting fruits (Regan et al. 1998) and “has evolved to contrast against background leaves in response to visual capabilities of local seed disperser communities (frugivores)” (Nevo et al, 2018).
To be efficient in foraging fruits, frugivores can see more colors than omnivores, other herbivores, or carnivores. It is much harder to spot purple, orange, and pink colored fruits in a green canopy without being able to see red colors! And additionally, the coloration give us information on the ripeness of fruits at a glance – even from a distance.
Illustration from the science journal PLOS ONE (Fedigan et al., 2014): Advantage of trichromatic color-vision for fruit foraging. See also an illustration in the journal nature on the effect of color-vision to distinguish colorful flowers within leaves (Hogan et al., 2018).
Our closely related ape family all share trichromatic color-vision (Jacobs, 2007). Not all primates have trichromatic color vision. A probable reason is that nocturnal species are not trichromatic. It comes as no surprise that the highly-frugivorous howler monkey is fully trichromatic.
Digestive anatomy is one of the key characteristics to determine the diet of an organism. Food is the driver behind the diversification of the digestive system (Karasov & Douglas, 2013). If humans have the digestion of omnivores or frugivore is somewhat controversial. However, the image of the high-meat-eating human is outdated and incorrect:
“Anthropoids, including all great apes, take most of their diet from plants, and there is a general consensus that humans come from a strongly herbivorous ancestry. Though gut proportions differ, overall gut anatomy and the pattern of digestive kinetics of extant apes and humans are very similar.” (K. Milton, 1999, Nature)
Humans have the intestinal mucosa of a typical frugivore!
The gastrointestinal mucosa absorbs nutrients and is adjusted to the type of food an animal has to digest. Therefore its size is characteristically for the diet type. In humans, the allometric size of the GI mucosa is specific for a frugivorous primate. Therefore humans are grouped with the frugivorous – not folivorous (leave-eating) or faunivorous (meat-eating) – primates! (Hladik, et al.1999) Quick reminder: frugivorous primates do occasionally eat meat and some animal-based foods, but much less than other dietary types.
Humans have the microbiome of a typical frugivore!
Humans have been shown to have a nearly identical microbiome to wild (frugivorous) chimpanzees when living in a natural environment (Gomez et al., 2019). What changes our microbiome is a “modern” polluted environment and diet (Sharma et al., 2020). Thus, humans naturally have a microbiome typical for a frugivorous primate.
4. Humans have teeth typical for frugivorous primates.
Human teeth have the same overall dental pattern as other frugivorous apes and primates. Teeth are the most important tool in food intake and foraging. Their shape essentially defines their function and what type of food we can process effectively. Frugivores take bites with incisors, and chew their foods with the molars while releasing sugar-digesting enzymes in their saliva. But when comparing frugivorous dentition to the dentition of other dietary types – like omnivores or herbivores – a few picture will tell a lot:
The teeth and dental structure of primates eating a high-fruit diet are very similar, as “form follows function” in biology.
Take as an example the “long-tailed macaque” living in south Asia. They are classified as omnivores because they eat fruits, leaves, fungi, and insects and also are known to eat crabs. Their preferred food, however, is fruits. It makes up the majority of its diet. Thus this primate species is also a frugivore – with a dental structure adapted to eat fruits.
This is the dentition of a chimpanzee, which is very similar to humans. See a detailed comparison between human and chimp teeth here.
5. Humans have complex hands optimal for foraging fruits.
Complex hands are the perfect tools for picking fruits from trees, determining ripeness, and peeling. To get the scope of this, picture picking and peeling fruits with a snout or paws will not work well – speaking from my own observation of my berry-eating dog!
As explained above, a sophisticated, functional characteristic – such as a complex hand – does not happen by chance as explained by Kimbra Cutlik in the Smithonian Insider: “Developing such complex hands was a costly evolutionary feat, requiring not only anatomical changes to the wrist and fingers, but also expanded nervous tissue to process sensory and motor signals between fingers and brain.”
What about climbing skills and arboreal skills?
Opposable thumb allow animals to grab and hold things and enables climbing. Primates share this with other arboreal (tree-living) species like pandas, squirrels, koala bears, and opossum (to name a few). But do humans have the climbing traits and skills for an arboreal life and, thus, for a fruit diet?
Humans have been argued to have reduced skills for arboreal life, i.e., tree climbing, but better adaptations of terrestrial bipedal life due to our “reduced” grip of the feet. However, it’s likely that through tree climbing training – since early childhood – arboreal life and fruit foraging seems possible. Thus the extent of possible arboreality of humans is still an open question in science.
“Our findings challenge the persistent arboreal–terrestrial dichotomy that has informed behavioral reconstructions of fossil hominins and highlight the value of using modern humans as models for inferring the limits of hominin arboreality.”
Venkataraman et al, 2012
Nevertheless, do reduced climbing skills and terrestrial adaptations – that ensured survival outside tropical forests, hunting and foraging other types of foods than fruits – generally speak against us being frugivores? Not necessarily, because
- Frugivores can be terrestrial (ground-living), too. (Havmøller, 2021)
- Bipedalism (walking upright on two feet) is also used on trees and has not necessarily evolved due to terrestrial living (read more here). This gives off some serious Avatar vibes?!
- Adapting to new challenging conditions (fallback foods) does not necessarily mean maladaptations to the prior conditions (high-fruit).
This, admittedly, is speculative, but in evolution, we need to consider different scenarios to reconstruct the real picture! Despite adaptations to terrestrial life, cooked foods (see below), and cold climates (see here), humans still have distinctive traits that have evolved with a high-fruit diet. A fact that appears to be largely ignored in human nutrition and dietary biology and evolution.
6. Sweet Taste Receptors help to detect energy-rich sugars in fruits.
Tasting and liking sweetness motivates us to eat ripe fruits. What gives fruits the sweet tastes are simple sugars, which are our primary energy source provided by the fruits. For us, liking sweets is natural and seems normal, but not all animals are able to taste sweetness! Especially species with a high meat-intake have lost their ability to taste sweet (read more here). Humans on the other hand do not find a raw, fresh piece of meat appealing nor tasty. Quite to the contrary, just looking at meat and blood is repulsive to most of us! This is why we do not take a trip to a slaughterhouse with our kids, but will be happily take them along with us to collect cherries or mangoes.
7. Frugivores like sour taste.
Acidic taste is off-putting for most animals – but not for frugivorous humans, apes, and birds! Just like sweet taste, humans enjoy sour taste. Most animals reject sour foods! We share our preference for slightly sour with all apes, and the frugivorous monkeys as well as birds. Once more, this is a typical feature for frugivorous species, as most fruits have some acidic, sour flavor to them. (This phylogenetic tree by Frank et al. (2022) shows acid detection and preference in different animal species.)
Being attracted to acidic foods could be linked to the vital necessity to get vitamin C (ascorbic acid) via the diet: sour is a good indication of vitamin C in the food. Thus, vitamin C detection and attraction could be vital and adaptive in species without functional vitamin C genes (see above).
8. Instincts tell us what looks and tastes like actual food in nature – mainly fruits!
Besides sweetness, there are other sensory cues that instinctively attract us to fruits. Why do we perceive colorful fruits, especially tropical ones, as extraordinarily appealing and beautiful in their natural state? Because we are biologically adapted to those fruits, which do not need any cooking or flavoring for us to love them in their ripe form. They smell and taste good , too! Those are all instincts that naturally guide us – like other animals.
We instinctually know that fruits are good for food, and to no surprise, wild tropical fruits are edible for us (Sayago-Ayerdi, 2021) – unlike wild temperate fruits, which evolved as food sources for birds (read more here). Unfortunately most of us have never experienced (or even thought about) the abundance, variability and nutritious value of tropical fruits – which is the fundament of a frugivorous diet for primates.
As small infants, after the lactation period, we are already instinctually attracted to sweet and colorful fruits, and sweet fruits are one of the first foods we can feed the little ones.
And if you like a small, convincing experiment about how important and strong instincts are, try feeding any cat some mangoes pieces…
Are humans adapted to cooked foods?
Generally, in nature, everything that is appealing straight from nature is a species’ naturally suitable food – this instinct is the key for every animal to know what to eat in the wild. Theoretically, everything that needs to be cooked to become edible or seasoned to be palatable and appealing is not natural human food. However, have we evolved with cooked foods, so that we can no longer be sustained by a raw diet? Unlike chimpanzees? The very short answer is no… but this topic calls for another article; see here.
9. We are a tropical species – the only habitat where bigger frugivores can survive!
Humans come from tropical ancestry and are actually still a tropical species (read more here). Only the tropics sustain larger frugivorous animals. Thus generally frugivorous mammals are found in the tropics. Bigger mammalian frugivores are exclusively tropical-native species. Why? Because only tropical conditions provide highly nutritious fruits throughout the entire year, as opposed to seasonal and cold climates. Thus, in temperate or colder climates we obviously cannot survive on mostly fruits.
Also, the lack of major biological cold adaptations, shows that humans are a tropical species. We just manage to live outside the natural habitat, because of our intelligent ability to shape cold environments into survivable conditions (heating, cooking, clothing, etc.). The “tropical human” is also supported by fossil records, which points towards humans being a species that originated in tropical Africa (Daanen, 2016).
Us being a tropical species is another indication that frugivory in humans is a real possibility, which is why most wild tropical fruits are edible for humans!
Conclusion
Knowing the human biological species-appropriate diet matters: the enormous ramification for dietary recommendations and habits, health, and the view on chronic diseases only becomes clear once we can see how wrongly we have eaten from a biological perspective. Most of us live entirely out of our natural habitat, which is why knowing the natural human diet is challenging. If we have never experienced the abundance, flavors and nutritional quality of high-quality tropical fruits, it is hard to imagine that we can live on mostly fruits.
Comparing and analyzing biological adaptations to diet and foraging is a valuable tool for exploring our species-specific diet. Humans have many adaptive features that specialize us as fruit-eaters. But are we still as frugivorous as chimpanzees? More scientists should ask this essential question! And as a follow-up question: “what can we learn from wild primate diets?”. Like this citation from K. Milton in Nature (1999) in her scientific work:
Want to know more about adopting a frugivore diet yourself? Check out our guide:
Go to How to do the Frugivore Diet
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