I often read on vegan health groups that humans are not meant to eat meat because our guts are long like those of the apes (who are predominantly plant-eating) vs. the short guts of carnivores (meat-eating animals). In fact, I used to argue this way myself in my vegan days. 🙂
However, once you understand a topic a bit better, the simplified and incorrect statements about it simply irritate you.
Human guts, when compared to those of existing apes, have similarities AND differences. Humans and apes show the same gut anatomy- simple acid stomach, a small intestine, etc.. However, humans stand apart from all apes: more than half of human gut volume is found in the small intestine while all apes have by far the greatest total gut volume in the colon; also the overall size of the human gut in relation to body size is small in comparison to that of apes.
What this means is that humans have adapted to a “high quality” diet. Here high quality means a calorie and nutritionally DENSE diet, which includes animal foods and tubers. A high quality diet for humans means that we need to eat a smaller volume of food to obtain the nutrients and energy we need.
The way our gut differs from apes says a lot. Most large primates have expanded colons, which is an adaptation to fibrous low-quality diets [“low-quality” here = highly fibrous foods such as leaves and bark]. The large colon allows fermentation of low-quality plant fibers (which allows extraction of additional energy in the form of volatile fatty acids). Our relatively enlarged small intestine (the principal site of nutrient digestion & absorption) and smaller colon reflects an adaptation to an easily digested diet that is nutrient-rich.
There is a general consensus that current hominoids (apes and humans) come from a strongly plant-eating ancestry. Apes, however, evolved into larger bodies that allowed to sustain themselves on lower quality diets. By eating both animal matter [to satisfy requirements for essential nutrients] and plant sources [primarily for energy] humans were able to avoid the constraints imposed by body size increases in apes (such as lower mobility and sociality in apes). Simply speaking: the bulkier they get and the more time they spend eating, the less they move around and the less social they are, which is a disadvantage compared to humans.
This dietary change in humans (adding animal and other dense foods), which departed from known plant-dominated diets of the apes, was eventually reflected in our brain size (much larger), overall form of our guts (shift in gut proportions, overall gut size) as well as dentition (smaller teeth, jaws). Concerning our particularly large brains: our brains are particularly energetically “expensive” as we expend a larger proportion of our daily energy on brain metabolism than other primates (in comparison to other primates, our brains are 3 times the size). Paleontologists believe that fast brain evolution happened about 1.8 mln. years ago and was associated with important changes in diet and foraging behavior (some argue it is specifically the addition of meat that allowed for such large brains to evolve). Apart from switching to high quality nutrition, humans show other adaptations to having a larger brain- compared to other primates we are “undermuscled” (less skeletal muscle) and fattier. Greater level of body fatness in human infants in fact helps grow a large brain by having stored energy and reducing energy requirements of the rest of the body (that has less muscle mass).
The point is: no, we’re definitely not “meant” to be vegetarian. Also, the point is not to say that vegetarianism doesn’t make sense for many of us. There are plenty of great reasons to avoid animal foods (ethics, environment, etc.), plus it’s easy to have an adequate veg. diet for adults with availability of supplements (vegan diets are not recommended for small children, though, considering brain development; the several vegan PhDs I know did not raise their children vegan specifically because of this) … but stating that we are not meant to thrive on both animal and plant sources is incorrect. Contrasting us with true carnivores [like cats] to show how very different we are (e.g. hey we don’t have claws and sharp teeth… um.. we however do have large brains to allow for sophisticated tool creation that replaces those) is also a terrible idea- we are not true carnivores either and have a dual dietary strategy [plants + animal sources].
Lastly, all this material should not support the notion that we ought to eat bacon 10 times a day.. meat clearly has a place in our diet, but this shouldn’t be used to justify a purposeful meat overload (I’m not sure what the benefit is for advocating heavily animal-based diets, considering modern animals are fattier and less packed with phytochemicals than the wild ones + there’s the whole issue of antibiotic and hormone use at the minimum. Unless, of course, you go on the “carbs are evil” side, but I am not in favor of that view… or you imagine our ancestors ate predominantly meat, which does not look to be the case since the diets varied dramatically depending on environmental circumstances).
(Note: I’m not pretending to actually be an expert on any of these topics; I simply read peer-reviewed articles and hang out with evolutionary anthropologists 🙂 ).
Milton, K. (2003). The critical role played by animal source foods in human (Homo) evolution. The Journal of nutrition, 133(11), 3886S-3892S.
Leonard, W. R., Snodgrass, J. J., & Robertson, M. L. (2007). Effects of brain evolution on human nutrition and metabolism. Annu. Rev. Nutr., 27, 311-327.
P.S. The bottom line is: these t-shirt designs are both incredibly dumb (disclaimer- i laughed a bit..but immediately felt guilty :D)