The Scientific Classification: Omnivores
From a biological perspective, there is a broad scientific consensus that humans are omnivores. This classification is not based on individual dietary choices, such as vegetarianism or veganism, but on the species' physiological and anatomical capabilities. The defining characteristic of an omnivore is the ability to acquire and process nutrients from both plant and animal matter, a trait that has provided our species with remarkable adaptability across diverse environments.
Biological Evidence: Teeth, Gut, and Enzymes
The most compelling evidence for human omnivory comes from our own bodies. Our anatomy represents a compromise between the specialized systems of strict herbivores and carnivores.
Dental Structure: Unlike the large, shearing canines of a predator or the broad, flat molars of a specialized grazer, human teeth are a mixed set. We possess sharp incisors for cutting, pointed canines for tearing, and flat molars for grinding. This combination allows us to process a wide variety of foods, from fibrous plants to tough meat.
Digestive System: The human digestive tract is also intermediate. At roughly 25 feet long, it is shorter than a herbivore's, which needs a longer intestine to ferment and break down tough cellulose, but longer than a carnivore's. Our saliva contains amylase, an enzyme that starts the digestion of starches, while our stomach acid is stronger than a typical herbivore's but less potent than a true carnivore's. This system is built for versatility, not specialization.
Nutrient Requirements: Our metabolism also confirms our omnivorous nature. We have specific biological needs, such as for Vitamin B12 and heme iron, which are most readily available from animal products. While supplements and fortified foods can provide these, they were historically obtained from animal sources, which confirms their necessity in our evolutionary diet.
The Evolutionary Journey
Human dietary evolution is a story of increasing diversity and adaptability. Archaeological evidence shows that early hominins had an omnivorous diet of plants and whatever animal matter they could acquire. A key evolutionary shift occurred with the increased consumption of meat and marrow, which provided energy-dense calories that some researchers believe helped fuel the rapid expansion of the human brain around two million years ago.
The control of fire and the advent of cooking further revolutionized the human diet. By processing food, our ancestors unlocked more calories, making food easier to digest and allowing for a greater variety of foods to be safely consumed. This reduced the energetic cost of digestion, freeing up resources for a larger, more powerful brain.
Understanding the Omnivorous Diet
A History of Adaptability
The ability to eat almost anything was a significant survival advantage for our ancestors. Omnivorous adaptability meant that when a food source became scarce due to environmental changes, our ancestors could simply switch to whatever was available. This behavioral flexibility enabled early humans to spread across the globe and thrive in vastly different environments, from tropical forests to the Arctic tundra.
Nutritional Pros and Cons
An omnivorous diet offers both advantages and disadvantages from a nutritional standpoint.
Advantages of a Mixed Diet:
- Nutrient Richness: A balanced omnivorous diet naturally includes a wide range of essential nutrients, from complete proteins and iron found in meat to fiber, vitamins, and minerals from plants.
- B12 and Heme Iron: Animal products are the most reliable source of Vitamin B12 and highly absorbable heme iron.
- Dietary Flexibility: This adaptability ensures survival during periods of scarcity when one food type is less abundant.
Potential Disadvantages:
- Overconsumption: The modern western omnivorous diet often includes excessive amounts of processed foods, sugars, and saturated fats, leading to increased risk of chronic diseases like heart disease and diabetes.
- Environmental Impact: A diet heavily focused on animal products generally has a larger environmental footprint than a plant-based one.
Comparison Table: Omnivore vs. Herbivore vs. Carnivore
| Feature | Herbivore | Carnivore | Omnivore (Human) |
|---|---|---|---|
| Primary Diet | Plants only | Animal meat only | Plants and animal meat |
| Dental Features | Large, flat molars for grinding; often have incisors for cutting plants | Large, sharp canines for tearing meat; scissor-like molars | Mixed dentition: incisors, canines, and molars for tearing and grinding |
| Intestinal Length | Very long to allow for fermentation of cellulose | Short to process meat efficiently | Intermediate length, shorter than herbivores, longer than carnivores |
| Stomach pH | Relatively weak (pH 5-6) | Extremely acidic (pH 1-2) | Stronger than herbivores, but less acidic than carnivores (pH 3-4) |
| Nutrient Source | Direct from plants | From prey (which ate plants) | Directly from both plants and animals |
Human Dietary Flexibility Today
While our biological classification is omnivore, modern humans exhibit incredible dietary diversity. Cultural and personal choices have led to a spectrum of eating patterns, and with modern nutritional science, it is possible for individuals to thrive on diets that emphasize or eliminate certain components.
- Vegan Diets: With careful planning and supplementation (especially for Vitamin B12), individuals can meet all their nutritional needs from plant sources.
- Regional Adaptations: Ancestral dietary patterns can influence genetic predispositions. For example, some populations have evolved lactose tolerance, while others have more copies of the gene for salivary amylase, aiding starch digestion.
- Health and Lifestyle: The health impacts of modern diets are often linked to levels of processing and physical activity, not just the plant-to-animal ratio. Indigenous hunter-gatherers, for example, were protected from many modern diseases by their active lifestyles, even with a meat-heavy diet.
Conclusion: The Ultimate Opportunistic Eaters
The question of what are humans classified as eating is best answered by looking at our biology and history: we are adaptable, opportunistic omnivores. Our evolutionary success was built on the ability to derive energy from a wide array of food sources, a trait reflected in our dental structure, digestive system, and nutritional requirements. While modern food systems and personal ethics allow us to choose highly specialized diets, our bodies remain a testament to a versatile, mixed-food past. The healthiest modern diet for an omnivore likely mirrors this ancestral adaptability—combining a variety of nutrient-dense plants and, for those who choose, well-sourced animal products, while avoiding excessive processed foods. This approach harnesses the full range of our physiological design to promote optimal health.
An extensive review of our evolutionary relationship with food can be found in National Geographic's exploration of the human diet evolution.
