What, exactly, are the physiological signs that humans are omnivorous? In other words, if I was an alien xenobiologist and I collected a few “samples”, how could I tell that humans ate both meat and plants?
I know that humans have both carnivorous, “tearing” teeth and herbivorous, “grinding” teeth, but are there other indications?
You partly answered your own question…
I think a big part of the answer lies in the teeth. Not only grinding and tearing but how thick the teeth are. Herbivores require more enamel to put up with the greater wear imposed by their diet.
In addition I think you might find something different in the digestive systems (although I’m not sure if this is wodespread enough to be indicative of an herbivore). Cows have a multy chambered stomach, cows and camels chew their cud, rabbits eat their own feces, etc… In all cases listed these animals need to do a lot of extra processing on the food they eat in order to extract as much nutrients as they can…this often means more than one trip through the digestive system. Meat has a much higher nutritional content on a pound for pound basis. I read somewhere that in proto-human hunter-gatherer societies females provided 85% of the food eaten (from vegetable and fruit gathered) but provided only half of the total nutritional intake of the tribe (the other half being 15% of the diet that was meat).
You’d just check out their shit. A little poo goes a long way.
Plant matter leaves fibrous remnants and undigested seeds in our doody. Animal matter leaves…well, I dunno what unique traces animal matter would leave. I’m sure someone will be by soon to tell us though.
Well, if that xenobiologist had been observing me at dinner this evening he/she could have confirmed that some humans are indeed omnivorous.
There was some barbequed pork (souvlakis) as well as greek salad, stuffed vine leaves, roasted potatoes, and fresh pita bread. There was also some sauteed asparagus with garlic and almonds.
Damn, that was some fine food. Made it myself too.
Anyways, field observations would quickly conclude the fact that humans are omnivores. They would also show that some humans really like greek food.
I suppose you were looking or a more scientific answer…
When in doubt, check in the Straight Dope archives: Are Humans Meat Eaters or Vegetarians by Nature?
I recall reading that herbivores have a long bowel, and carry a large population of bacteria to digest the cellulose for them. Carnivores have a short bowel, since meat has no cellulose and is easy to digest. (IIRC, pandas eat 16-18 hours a day, since they’re really carnivores that switched to bamboo quite recently, and can’t digest it very well in their short bowels.)
Humans, I suspect, have a bowel of intermediate length.
Ahem. Of course. I missed that.
However, upon reading, Cecil seems to give exactly two reasons why humnas are omnivorous:
No mention of Greek food whatsoever.
But…is there anything else? Do we depend a nutrient intake that is most easily obtained through a mix of meat and veggies? Do we secrete stomach enzymes that can be associated with both meat and plants? Is the fact that humans are able to extract nutrition from both plants and animals evidence in and of itself that we’re omnivorous?
I’ve always thought that binocular vision was a sign of a predator. There are probably exceptions to the rule, of course, like with things that don’t use their eyes to hunt. But even in avians, there’s generally a higher “crossover” in the visual arcs of hunters than prey. I could be talking utter tripe, but it’s a thought.
Isn`t there also a particular vitamin (in the B family, I think -B12?) that is mainly obtained from animal products such as meat? I would suppose there are particular enzymes produced in order to digest meat, though I don’t really have any cites for this. Maybe when I go home I’ll get a chance to look in my Biochemistry textbook. There may be something there.
IIRC, humans are dependent (in the absence of synthetic supplements) on animal sources for vitamin B12. Plants don’t make it, and the human body doesn’t synthesize its own. B12 deficiency causes pernicious anemia and sometimes neural inflammation.
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I recall reading somewhere a discussion between a vegan and one of my fellow omnivores, in which the vegan suggested that not washing vegetables would allow you to ingest B12 from residue on the plant. The omnivore politely declined, saying that he preferred eating animals to eating their fecal residue.
I wish I could find that site again. I’ve got nothing against vegetarians, but I found it amusing.
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Slight hijack here, but I recently heard at the San Diego zoo that pandas have only recently evolved into vegetarians from carnivorous ancestors. They eat only bamboo, and are only able to process about 20% of what they eat because their gut isn’t totally adapted to being a plant-eater.
Would an alien even know how to classify food as meat and plants? They probably have a different food source on its planet, if they need to eat at all.
The amount of proteins/enzymes secreted when you eat for digestion of both proteins and starches far exceeds the amount need to digest the normal amount of food in one meal. This would indicate that both of them have been a part of our diets for a very long time.
Primates in general have good depth perception, which seems more related to swinging through the trees than to being Mighty Hunters. (Being able to judge just how far away that next branch is is an obvious plus for an arboreal critter.) That said, omnivorism goes way back with primates:
(Hmmm…the structure of that sentence is a little odd: “Although nonhuman primates will occasionally eat the flesh of other mammals, their diet consists primarily of…[among other things] rodents.” Rodents are mammals, aren’t they? I guess the author just meant that rhesus monkeys don’t take down too many wildebeest.)
At any rate, eating anything that doesn’t move, and most things that do, seems to go way back with us primates.
From The Merck Manual, Sixteenth Edition p. 954:
“The most common form of true vegetarianism is **ovo-lacto vegetarianism **in which meat and fish are eschewed. Iron deficiency is the only risk… Vegans consume no animal products and are susceptible to vitamin B12 deficiency. Yeast extracts and fermented foods of Oriental origin provide this vitamin. Ca, Fe, and Zn intakes tend to be low. A fruitarian diet consists solely of fruit, is deficient in protein, salt, and many micronutrients, and cannot be sustained for long.”
In addition to the above, getting a full complement of amino acids on a vegan diet is something of a challenge. This may explain why rice and bean dishes are staples of many ethnic cuisines: that combination provides complete protein. Undigestible sugars contained in this combo also–ahem–produce something else in the human digestive tract that suggests this wasn’t the way nature intended for us to eat.
At first I thought the OP might be a militant vegan troll, but ZUT’s later post dispelled that notion.
This is the approach I was going to take. The three catalytic enzymes I remember from Biochem are Trypsin, Chymotrypsin, and Elastase. IIRC they are used for breaking down specific configurations of protein molecules into smaller subunits, which eventually get broken down further into their constituent amino acids.
If these aliens could figure out what these enzymes were used for and subsequently searched for a rich source of protein substrate for these 'zymes to work on, they’d conclude meat is what they’re meant for.
Interestingly, us humans don’t have any enzymes which allow us to break down collagen (primarily used in animals as a structural tissue) which is made entirely of protein.
Hey! Sheesh; you try to ask a serious question… Actually, I suppose my OP could be interpreted as you say, but I was trying to be concise, so I left out the intro, which was: “My wife and I were at supper, eating pork tamales (pretty much the epitome of an omnivoric meal) and discussing human physiology, and we had a question…”
But, using just this information, the aliens would conclude that we’re carnivores, not omnivores. Are there complementary enzymes (as USCDiver mentions) that are dedicated to digestion of plant material? My question wasn’t just “how can we tell that humans are meant to eat meat?”, but rather, “how can we tell that humans are meant to eat meat and plants?”
Interesting question. I was all set to give you my #2 patented answer, but happened to remember a few little things.
Researchers have discovered that certain vegetarian animals will consume meat, especially around the time they bear young, like those cute little squirrels, obnoxious chimps, and some turtles thought to consume mainly grass, insects and small fish.
Then you consider the fact that someone started grinding up cow remains to feed right back to the cows in their vegetable feed, so the digestive process of a purely vegetarian animal can handle meat proteins easily. (The British, wisely, and after this Mad Cow mess, banned the process of mixing animal remains into the feed of cows, chickens and everything else.)
So, I had to rethink a few things and came to the conclusion of the following:
Humans have the primary stance of a prime predator, being bipedal to elevate the brain and eyes, which use binocular vision, color perception along with a great variable range of focus, high above the ground to, among other reasons, spot prey.
The hands bear the remains of claws, so do the feet, which appear to have once been another set of grasping, clawed hands.
The legs are designed with massive muscles for speed, the feet designed to dig into the turf, the body streamlined (unlike a cow, though there are exceptions) the nose is hooded to form a rain shield and contains a massive amount of olfactory nerves to smell in a great range.
The teeth are the biggest give away, though. Sharp front teeth designed only for cutting, vestigial ‘fangs’ for penetration and gripping, then hard, blunt teeth for grinding and mashing.
The eyes are recessed into the bony skull for protection, the ears close to the side of the head for the same reason and convoluted for maximum amplification of sound. Plus, the mouth itself opens wide enough to elevate the ‘fangs’ into an outward jutting attack position.
The hands are designed, with an opposable thumb, to grasp and hold tightly with an astonishing amount of power due to the design of the muscles. (This is also found in vegetarian monkeys, but the chimp discovery leads many to believe that they might not be pure vegetarians after all or might have been descended from omnivores.)
Plus, the human has a very large brain case in comparison to the relatively small body. Pure vegetarians usually have a much larger body in comparison to the size of their brain because it takes a tremendous amount of greens to be processed to fulfill the protein and other nutritional requirements in relation to the much smaller amount of meat.
The result? A prime predator.
Well, sorry Who?26, but the comparative anatomy you list doesn’t imress me as much of an arguement that humans are a ‘prime predator.’ It pretty much all applies to gorillas and chimpanzees which, while they may eat meat occaisonally, are certainly not prime predators.
As a general rule, binocular vision is more useful for predators, while having non-overlapping visual fields that cover more of the horizon is often more useful for prey, but this is by no means universal. A strong visual orientation (such as humans have) is also perhaps more likely in a predator, but not a dead give away.
Nothing else seems to be a convincing argument for predator status – kangaroos are bipeds (along with gorillas; I can’t think of any other quadrupeds that don’t have at least ‘remains’ of claws (and humans are pretty darn wimpy in that respect); opposable thumbs are found in all kinds of primates; human facial structure is indeed based on binocular vision, but our sense of smell is pretty sad in comparison to the animal kingdom generally; and our teeth are tremendous evidence that we’re omnivorous (and as well, an alien looking at our (lack of) jaw muscles might be able to figure out that we eat only very high quality foods (i.e. cooked))
That big ol’ braincase, and what’s inside, does give us the means to be a pretty fearful predator, but also gives us the means to be an amazing cooperative grower of food. It’s all in how we use it.
No, human anatomy does not suggest an evolved predator, much less a “prime” one.
In fact, I would imagine that for most of our evolutionary history, we were more often prey than predator. Mostly, we were foragers and scavengers, and these types of feeding behaviors are typically associated with an omnivourous diet - eat whatever you can get your hands on. (And any parent can attest to the fact that this behavior is hard-wired.)
But the best proof I can offer for humans being omnivorous is: I CRAVE PIZZA. Super supreme, preferably.