What chimpanzees teeth reveal about the human diet
Dental structures are important anatomical traits to investigate the diet type and dietary ecology of a species. Thus, by studying the chimpanzees’ dentition and diet in the wild and comparing it with human dentition, we can learn what our natural diets have in common. After all, it is the striking similarities between human and chimpanzee teeth that have convinced a growing number of people to adopt a high-fruit diet – inspired by the chimpanzees!
Our primate cousins are highly frugivorous (specialized in eating ripe tropical fruits). Therefore the question here is, are human teeth those of a frugivore, too? In this article, we dive into the similarities and the differences (mainly bigger canines and thinner enamel in Chimpanzees) and see what this means to approach this question.
To know more about the anatomical similarities and differences between our teeth and Chimps’ teeth, I asked a zoologist. Here is what he found (and what I had to add):
The dental structure plays a critical role in determining the food preferences of an animal species. Tooth shape, size, structure and position help to shed light on their distinct evolutionary history regarding diet. This is no different for humans and chimpanzees – our closest primate family.
Primates have been confined to tropical latitudes (Emes et al., 2011) where they have evolved in tropical climates and with tropical food sources. This includes humans, which originated in tropical Africa (Daanen et al., 2016). Chimpanzees and humans are classified together in the superfamily Hominidae and share approximately 98% of DNA, which explains the close similarity between their dentition (Machanda et.al. 2015).
The teeth of primates (for this case, humans and chimpanzees) can be distinguished based on position, form, and function into incisors, premolars, canines, and molars; this is the heterodont dentition.
We know that form follows function. Hence it is not surprising that humans and chimpanzee dental function seems very much the same: According to Machanda et al. (2015), in the dental structure of both human beings and chimpanzees, the functions of the various types of teeth are comparable; incisors aid in cutting, canines enable piercing and ripping, while premolars and molars facilitate grinding. This indicates that their species’ diets are very similar.
But to get a better idea of what characteristics the dentition of Chimpanzees and Humans have in common, and also in what they differ, let’s look at the anatomy in detail: Let’s compare the dental structure in more detail to find out how similar they really are:
Similarities between chimpanzee and human teeth
List of morphological similarities of chimpanzee and human dentition:
- Number of teeth: Humans and Chimps both have 32 teeth.
- Same Number of each type of tooth: We share the heterodont dental formula (18.104.22.168) with Chimpanzees. The dental formula represents the number of the four types of teeth (2 incisors, 1 canine, 2 premolars, and 3 molars for each side). Their teeth can be distinguished based on position, form, and function into premolars, canines, incisors, and molars.
- Two sets of teeth: Both humans and chimpanzees are diphyodont, with dental changes after the juvenile life stage: We grow milk or deciduous teeth, which fall off as the baby matures, and then develop a permanent set of teeth in place of the milk teeth (all their deciduous incisors, molars, canines, and premolars have a single set of replacement teeth). Numerous baby teeth persist till some permanent teeth are in place.
- Periodontal ligament: The dental roots are attached to a bony alveolus through a suspensory ligament (Emes et al., 2011).
- Enamel formation: Recent histological research studies on the formation of enamel crown in primates have suggested numerous resemblances during the time of molar formation in both chimpanzees and humans.
- Anatomy of the root canal: The anatomy of the root canal varies depending on the type of tooth as well as the morphology of the root.
- Gradient of the thickness of the molar enamel: The enamel thickness increases from the anterior towards the posterior section of the jaws of both humans and chimpanzees (Machanda et al. 2015). Smith et al. (2008) postulate that the front-to-back increase in the thickness of the enamel in both humans and chimpanzees may be associated with the varying bite forces along the rows of the teeth.
- Premolars cusps: The cusps are used for sharpening the canines.
Differences between chimpanzee and human teeth
When looking at differences between human and chimpanzee teeth, we need to keep in mind, that we are looking at two distinct but closely related species. This means that while there are differences, the overall dental pattern is shared!
To put the extent of the differences into perspective, if we compare humans to other mammals like giraffes (folivorous herbivore), pigs (omnivore), or wolves (carnivore), the differences in dentition are of magnitudes larger, than when comparing humans and Chimpanzees. Because those animal species have a completely different dietary ecology than we do!
That said, there are evident differences in relative jaw size and shape, as well as the extent of canine growth, plus a few smaller differences, which might give us a hint about differences in the diets of humans and chimpanzees.
List of morphological differences between chimpanzee and human dentition:
- General teeth size: Humans have smaller molars and premolars. Chimpanzees’ incisors are broad and spatulate (the anterior teeth are relatively larger than the posterior ones while in human beings, the posterior teeth are larger than the front teeth).
- Size of the canines: Humans have smaller canines than Chimpanzees. Also, besides canine size, there are some other remarkable differences in canines and questions related to function (diet type) that deserve a discussion on their own (see below). Additionally, chimpanzees have large interlocking canines to the extent that the distal exteriors of the upper-jaw canines establish contact with the anterior surfaces of their third premolars on the lower jaw (Harcourt-Smith, 2010).
- Sexual dimorphic canines: Canine teeth of chimpanzees are sexually dimorphic, those of humans are not.
- Enamel thickness: Chimpanzees have relatively thinner enamel than humans. See what this means in terms of function and diet below.
- Number of cusps of premolars: Premolars in humans are bicuspid, the premolars in chimpanzees have between 4-7 cusps.
- Relative Jaw size: The Jaws in human beings are smaller, more gracile, and project less in comparison to those of chimpanzees of their equivalent size.
- Jaw shape: The lower and upper jaws of chimpanzees are U-shaped, with parallel molar rows, with teeth diverging anteriorly (Machanda et.al. 2015). On the contrary, human beings have shorter lower and upper jaws which are either V or bow-shaped, with teeth separating posteriorly and their dentition are comparatively uniform both in shape and in size (Smith et.al., 2007).
- Diastema: Chimps have a gap beside their canines and incisors.
- Roof of the mouth: The palate (roof of the mouth) in humans is largely arched. Chimps have a flat palate.
- Diastema: Chimpanzees lack a diastema.
- Timing in dental root development: In Chimpanzees, the peak in root growth rate corresponds with the time a specific tooth commences functioning. This allows chewing on the tooth to start as soon as possible. However in humans, the spurt comes before eruption, while the teeth are still hidden under the gums – as a result chewing on the teeth does not start immediately (Dean & Cole, 2014).
Do the dental differences in humans and chimpanzees point towards a different diets?
Some studies have associated the differences in structure and function of human and chimpanzee teeth to their evolutionary adaptations to feeding and general survival. What are the possible dietary differences indicated by canine size and enamel thickness – the two main traits that deviate between the two species?
Humans have smaller canines which are spade-shaped, tiny incisors. On the other hand, chimpanzees’ canines are long and sharp. Also, the dimorphism between males and female canines in chimpanzees is notable here – male chimpanzees have canines that are significantly larger and longer than those of their female counterparts.
Do the bigger canines in chimps have a function in dietary ecology? Typically enlarged and sharp canines are also associated with meat consumption. However, while hunting in chimpanzees is well-studied, there is no evidence to support that the bigger canines serve in hunting or meat-eating. On average, only 1-2% of their diet is meat, and in some individuals, it’s not clear if they consume meat at all. However, when they do, the hunting and handling of the prey’s flesh is male business. Thus the large canines in males might play a role in this behavior, too. This is purely speculative, though!
Human canines do not exhibit sexual dimorphism (Smith et al., 2007). In humans canines are much reduced in size and have almost lost their function. Therefore it seems possible that humans are biologically less equipped to hunt and eat meat than Chimpanzees. This would go in line with the instinctual and sensory behavioral difference: while chimps do eat raw meat and insect, to most humans, those animal foods do not look, smell or taste appealing straight from nature (uncooked and unseasoned). But again, this is just an observation that lead to an unproven hypothesis!
Is thicker enamel in humans adaptive to fallback food?
Enamel thickness is thought to be adaptive to the dietary ecology of a species. Humans generally have the thickest enamel of primates. Chimpanzees, on the other hand, have relatively thin enamel.
But what does this difference tell us about dietary differences between humans and Chimpanzees? In short: not so much as previously thought! Seraching through scientific literature, there seem to be still more open questions than answers, and different hypotheses on the adaptive function of enamel thickness are being discussed and challenged. Thick enamel could have evolved due to the following:
- A diet that includes more hard foods. This is the most common stated hypothesis, but also is often questioned.
- Selective pressure from abrasive foods (like silica-rich phytoliths, leaves or acids) and gradual abrasion during a long lifespan.
- Living in temperate climate and the seasonal foods variability – as opposed to tropical climate and fruit-availability.
Adaptation to crush hard foods?
Thick enamel is generally thought to be advantageous to crush hard foods, like nuts, roots, tubers, and seeds, while thinner enamel is due to a soft fruit-rich diet. This would indicate that humans either preferred hard foods, or had to eat more fallback foods because they left fruit-rich tropical areas and thus developed more suitable teeth for “durophagy”. However, a 2014 Harvard study found that enamel thickness could not support the hard-object feeding dietary pattern, at least in macaques: “Enamel thickness across the genus Macaca did not vary as would be expected if abrasive tissue loss, degree of folivory, or inferences of hard-object feeding of preferred or fallback foods served as strong selective pressures.” (Kato et al., 2014) They also stressed that their findings are preliminary.
Adaptation to seasonal environments?
They did, however, find that “enamel thickness was strongly associated with geographic distribution; macaque species in temperate environments had thicker enamel than did macaque species with tropical distributions… suggesting that thick enamel may be adaptive in seasonal environments. Additional research is needed to determine if thick enamel in temperate macaques is a response to intensified hard-object feeding, increased abrasion, and/or a broader diet with a greater range of food material properties” (Kato et al., 2014) This pattern along the climatic zones well-fits to explain the difference in enamel thickness in tropical chimpanzees and “temperate” humans, which again suits the fallback-food idea mentioned above.
Adaptation to the migration out of the tropical forests?
Ripe fruits were less available to humans when they migrated out of the fruit-rich, tropical forests. Thus they had to start eating more hard foods to survive – fallback foods (including savannah type environment)! Was this a potential selective force to drive the evolution of thicker enamel? If yes, strong enamel might be an advantageous adaptation to a diet outside the former fruity paradise.
Due to the ecological conditions found in temperate climates, cold-indigenous people show to have some traits that have changed and adapted to local diets (i.e. improved milk digestion) and thermoregulation. However, adaptations that emerged due to selective stressors encountered in the new environment do not signify that humans are now optimally adapted to the new environment. Humans remain a species that is largely adapted to tropical climates and habitat, including the food sources, as the migration has taken place much faster than most evolutionary changes can take place. Humans were able to survive outside their natural, warm habitat, because of cultural adaptations, like cooking and the use of fire and heating. See this article here, for more in-depth understanding.
Humans have biologically co-evolved with tropical fruits as seed-dispersers and people from temperate climates that “return” to live in the tropics report and enjoy enormous health benefits.
The appearance of the chimpanzee and human teeth is strikingly similar. We can even see with our own eyes how much our dentition resembles each other – compared to a cow or dog. That’s why we just love the chimpanzee smile, as we can recognize ourselves in it! And the anatomical comparison confirms the similarities.
Further, the dentition structural similarities suggest a similar function – which calls for the conclusion that the dietary biology of humans is highly likely closely related to the one of chimpanzees – a high-fruit diet!
The main morphological difference lies in the bigger canine size in male chimpanzees, which does not seem to play a major role in diet (meat-eating), but rather social behavior. Further, there is one trait (enamel thickness) that points towards an adaptation of humans to temperate climates and the foods of temperate climates when they migrated out of the tropics. They had to survive in sub-optimal habitats for frugivores – while chimpanzees did not. This does not mean though, that humans are not still very-well adapted to a highly frugivorous diet.
Our frugivorous cousins’ teeth are so similar to our own that it is very hard to deny that the species-appropriate diet is probably extremely similar. Here is where instinctual knowledge might answer some of the remaining open questions: what foods look, smells, and taste good to us when coming straight from nature? No cooking, seasoning or other processing allowed, though…
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