A battle has been raging between two factions—the vegetarians vs. the meat eaters. Both sides claim with passion and ferocity that their dietary principles represent the natural order of consumption.
But what is the ultimate truth? Are humans by nature herbivores, meant to consume plant life for nutrition, or are our predatory instincts the norm for a primarily carnivorous diet?
Most of humanity munches away on whatever they want, without much concern about the evolutionary aspects of eating greens or red meat. But there are some biological characteristics that determine what we can and should consume.
The Guts of the Matter
A look at other animals provides us with some interesting insights. Cats, for example, typically have intestines that are only 3½ times their body length. True carnivores rarely have intestines exceeding body length by more than 6 times.
Compare that with milk cows, whose bovine digestive tracts measure 20 times their body lengths. Most herbivores do not have intestines shorter than 10 times body length.
Clearly, carnivores have intestines that are adapted to quick processing and disposal of flesh, hence the shorter length. A grass-eating herbivore will generally have longer intestines, as well as specialized sacs for optimal absorption and effective processing of plant cellulose.
As for us humans, we have intestines that are around 8 times our body length. That’s roughly midway between confirmed meat-eaters at one end and strict vegetarians at the other.
Common and Uncommon Traits
But there are other factors to consider. Jaw shapes and the existence of flat molars suggest that humans are akin to herbivores, as does alkaline saliva compared to the acidic saliva of most carnivores.
However, the presence of human “canine teeth” suited for ripping and tearing flesh might suggest a closer relationship to animals that eat their kill. Our single-chamber stomachs resemble those of carnivores, too, unlike the multiple chambers common among herbivores.
Many say all of this evidence supports the possibility that humans are natural omnivores —an offshoot of our ancestor’s opportunistic and diverse dietary habits. But omnivores usually have large mouth openings relative to head size, they hyperventilate to cool down rather than perspire, and many have claws in contrast to our short, flattened nails.
Our Evolving Diet
Vegetarians stand by their conviction that we humans were practically built for a no-meat diet. They say we have acquired an unnatural carnivorous diet with negative consequences. They point to the emergence of heart disease and certain cancers that have been scientifically attributed to the growing consumption of meaty fast foods and juicy steaks.
Evolutionary research indicates that we probably started off as frugivores (fruit-eaters). Our Homo erectus predecessors had an almost exclusive diet of prehistoric fruits.
Our Neanderthal ancestors, on the other hand, were apparently pioneers in the acquisition of meat as a dietary staple. The shift in eating habits might have been crucial to the survival of their species. It grew out of need, not nature.
A New Theory Emerges
The most recent theory holds that we are, in fact, neither carnivores or true ominvores. We are herbivores that can eat like carnivores, so we do.
Flash forward to the present day and the question remains—should we eat meats or beets? The answer might still be found in our habitually opportunistic eating behaviors.
We rely on the current contents of the supermarket shelves and of our fridges to guide our choices. We allow our cultures, and what’s readily available, to define us. We eat what we choose, not necessarily what’s best for us.
Cavemen ate meat to survive. Must we, too?
Alfablue, February 2013