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What would be the major changes to our bodies if we were herbivores? Would our bodies be weaker because they were not getting any protein from meat? Would we be completely different? (Probably, I suspect).

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    $\begingroup$ There actually are people who don't eat any meat at all. I'm not a fan of soy but apparently it counts as a source of proteins as well. $\endgroup$ – John Dvorak Nov 30 '14 at 10:31
  • $\begingroup$ @JanDvorak I know there are people who dont eat meajust. Im saying like thousands of years back we just stopped eating mear. How would that affect us now? $\endgroup$ – CrazySlayaNinjaBear Nov 30 '14 at 10:58
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    $\begingroup$ What kinds of fruits/vegetables/legumes/whatever are we eating? Things that grew in Africa? $\endgroup$ – HDE 226868 Nov 30 '14 at 13:54
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As far as I can tell, the major changes would be to the human digestive system, as well as to all body parts involved in processing food.

Teeth

The teeth of carnivores and herbivores differ because they eat different things, which require different techniques to chew. Plant matter is a lot different in consistency when compared to a slab of meat. Wikipedia has a nice note on the subject:

The shape of the animal's teeth are related to its diet. For example, plant matter is hard to digest, so herbivores have many molars for chewing and grinding. Carnivores, on the other hand, need canines to kill prey and to tear meat.

Our teeth are best suited to eat both meat and plants; if we became herbivores, I would expect that our molars would develop even more, while our front teeth would become less developed.

Stomach

As you mentioned there are conspicuously low levels of protein in plants. Herbivores, as a whole, will most likely receive a different set of nutrients than carnivores. Stomach enzymes and fluids work to break down different substances; we would see a change in these enzymes and acids as more plant matter was introduced into our diet.

If Wikipedia is correct, the major protein-processing enzymes include proteases and peptidases. We might see reduced numbers of these in a group of herbivorous humans. These acids are active all over the digestive system, so other organs would be affected


Would our bodys be weaker because its not getting any protein from meat?

Have you ever fought a 400 lb gorilla? Exactly.

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Humans are omnivores, this has resulted in our digestive system evolving as it has. However, if humans had evolved as herbivores, then the following changes would be necessary:

Teeth:

Human teeth are actually fairly well adapted to a herbivorous lifestyle already, albeit herbivory that includes mostly fruit and nuts and soft leaves. Were humans to evolve as leaf/grass eaters (lower quality food), teeth are worn down rapidly by such a diet, and the molars would have to be larger and would either have to be replaced frequently (as in elephants) or be open-rooted so as to grow continuously (as in horses). The incisors may also have to be open-rooted, depending on if they are used to strip leaves off branches, or if they are used to crop grass. The numbers of teeth - and the size of the mouth - depends on the method by which the diet is digested.

Gut:

A herbivorous diet with lower-quality food requires a considerably higher amount of treatment in the gut than human's current diet. There are two ways this can occur:

Foregut fermenters (such as cows) have large stomachs in which their food is stored in a bacterial soup which aids its digestion. They are able to regurgitate their food in order to chew it later. They have long intestines to maximise the digestion of the pre-treated fodder. However, if they eat food that is too rich, they tend to suffer from bloat as the foregut bacteria metabolise and reproduce out of control.

Hindgut fermenters (such as horses) have normal sized stomachs, long small intestines, and an enlarged caecum (that in humans is the appendix) before the large intestine. Hindgut fermenters must chew their food more thoroughly (and must therefore have more grinding teeth, hence the answer to the question about horses, "Why the long face?") than foregut fermenters. Partially digested food accumulates in the caecum, where it undergoes bacterial fermentation, however, high quality food is not an issue, since the pre-treatment in the foregut would have removed the high-quality components, leaving only the difficult-to-digest stuff. However, hindgut fermenters are not quite as efficient as foregut fermenters. (As a diversion, this is why horses can be fed apples, but cows cannot.)

A human-sized herbivore would likely gain more advantage from a foregut-fermentation digestive system, as it would not require as great a change in dentition, however a hindgut fermentation system would allow a greater variety of food. Gorillas, who are primarily herbivorous, are hindgut fermenters.

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OK, it looks like nobody mentioned one major difference.

BRAIN SIZE

Research indicates that human brain sized increased very rapidly as our ancestors switched from a primarily herbivore diet to including meat in their food.

http://www.livescience.com/24875-meat-human-brain.html

http://www.livescience.com/23671-eating-meat-made-us-human.html

http://www.npr.org/2010/08/02/128849908/food-for-thought-meat-based-diet-made-us-smarter

http://www.nasw.org/article/eating-meat-drove-evolution-our-big-powerful-brain

http://www.berkeley.edu/news/media/releases/99legacy/6-14-1999a.html

LARYNX

Meat eating means hunting. Hunting means group activity. Group activity means communication. Communication means sending and receiving complex detailed informational messages. Detailed messages in short time mean the need of producing many types of sounds. Many types of sound production means you need a larynx not deep down your throat like the gorillas have, but right up up up at the top of the throat the way we have now.

https://books.google.com/books?id=FgX2wcQXHTgC&pg=PA159&lpg=PA159&dq=meat+larynx+position&source=bl&ots=0NJ45Rkqx-&sig=4dtQt88fPFM1Z4u5CEfebi5VRBw&hl=en&sa=X&redir_esc=y#v=onepage&q=meat%20larynx%20position&f=false

There are several other important changes related to meat diet, but most of them are about the psychology and social structures of early peoples, so I will not mention them here.

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    $\begingroup$ Eating meat does not necessarily imply actively hunting, and hunting certainly doesn't necessarily imply group activities. Plenty of scavengers eat meat but don't hunt, or hunt only rarely. Plenty of carnivorous species are solitary animals which basically limit their non-hostile interactions with others of their species to procreation. The three might be related in a species such as humans, but evolution could have taken a different path here, or humans could have evolved from a less social species. $\endgroup$ – a CVn Sep 10 '15 at 21:23
  • $\begingroup$ Take any stage in human evolution (sahelanthropus, orrorin, australopithecus, whichever you want), read their physical properties (power, speed, stamina) and then explain to me how on earth they could have ever gone hunting alone! As for scavenging, remember that early humans were limited to africa. When we talk africa, we are talking about hyenas as the primary scavengers of the ecosystem. Are you telling me a solitary human could outcompete a pack of hyenas in scavenging? $\endgroup$ – Youstay Igo Sep 11 '15 at 2:26
  • $\begingroup$ Did I ever say either? Your claim was that (and I quote you directly) "Meat eating means hunting. Hunting means group activity.". I showed that this is not necessarily the case. It happens to be the case in the case of humans as evolved, but that does not make the general statement valid and it could have turned out quite different. Since the question as asked posits a quite large difference from what humans are, statements that can be rendered invalid by similar differences could use more explanation, IMO. $\endgroup$ – a CVn Sep 11 '15 at 7:11
  • $\begingroup$ Not my downvote, by the way. $\endgroup$ – a CVn Sep 11 '15 at 7:13
  • $\begingroup$ You are right. My statement is fit only for what "did happen" in the human evolution and not "in all possible cases of vegetarianism". But you are forgetting that the question title is => What would be the major changes to our body if we WERE herbivores? So this is not a theoretical issue with generalities, but specifically limited to human evolution as it occurred. So the indigenous factors all count. Plus, I don't build a grudge for anybody who downvotes me. You don't have to be so defensive. $\endgroup$ – Youstay Igo Sep 11 '15 at 7:16

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