Why Do Chimpanzees Eat Meat?

Chim­panzees eat meat for two sim­ple rea­sons: they can catch it and they like it. Chim­panzees are par­tic­u­lar­ly like­ly to eat meat dur­ing the dry sea­son, when short­ages of the foods that nor­mal­ly make up the bulk of theirdi­et cause them to lose weight. Although the meat may be a use­ful source of calo­ries dur­ing the dry sea­son, wild chim­panzees don’t need to include meat or any oth­er ani­mal-based food in their diet to ful­fill their needs for pro­tein or any of the amino acids. In fact, plants pro­vide all of the nutri­ents that are known to be essen­tial for a chim­panzee, except for vit­a­min D (which they get from the abun­dant sun­shine in Africa) and vit­a­min B12 (which comes from bac­te­ria).

Many peo­ple think that I am sil­ly for ask­ing where goril­las get their pro­tein. They tell me that I should talk about chim­panzees instead. Often, they inform me that chim­panzees are far more sim­i­lar to human beings than goril­las are, as if I couldn’t tell that just by look­ing. These peo­ple are miss­ing my point: goril­las are the largest and most pow­er­ful liv­ing pri­mate and yet are the clos­est to fol­low­ing what human beings would con­sid­er a veg­an diet. Chim­panzees and human beings don’t need to eat meat to grow up big and strong because goril­las grow up to be far big­ger and stronger with­out it. Lawyers may rec­og­nize this as an a for­tiori argu­ment.

If a male goril­la, whose diges­tive sys­tem is prac­ti­cal­ly iden­ti­cal to a human being’s, can get enough pro­tein from veg­eta­bles to grow to weigh more than 400 pounds and be ten times as strong as a man, why shouldn’t I expect that a rel­a­tive­ly puny human Olympic weightlifter could also get enough pro­tein from a plant-based diet? My intent is to ridicule the Four Food Groups dog­ma that I was taught in sixth grade.

Goril­las don’t hunt or fish, and they don’t keep cows or chick­ens. As a result, they don’t eat meat or fish, dairy prod­ucts or eggs. The only ani­mal-source food they eat is “the oth­er, oth­er white meat”: ter­mites, slugs, and oth­er creepy-crawlies. These foods would make an insignif­i­cant con­tri­bu­tion to the goril­las’ pro­tein intake, which is already high because pro­tein accounts for a high per­cent­age of the calo­ries in leaves.

Bugs and slugs could be a use­ful source of vit­a­min B12, a micronu­tri­ent that is made by bac­te­ria in their intestines. Vit­a­min B12 is also pro­duced by bac­te­ria in a primate’s gas­troin­testi­nal tract. How­ev­er, the vit­a­min may be pro­duced so far along in the intesti­nal tract that it isn’t absorbed effi­cient­ly. No plants make vit­a­min B12, but goril­las and chim­panzees can prob­a­bly get enough vit­a­min B12 from the bac­te­ria in the bugs they eat and in the dirt that clings to their food. Plus, apes are not metic­u­lous about wash­ing their hands, if you get my drift. If you are wor­ried about get­ting enough vit­a­min B12, you don’t have to eat dirt or bugs. You can get it in a nice, clean tablet instead.

I don’t ask where chim­panzees get their pro­tein because chim­panzees do eat some meat. Chim­panzees prob­a­bly eat less meat than just about any human pop­u­la­tion oth­er than Bud­dhist monks. Nev­er­the­less, many peo­ple want to use chim­panzees’ meat con­sump­tion as an excuse for humans to eat meat.

The fact that chim­panzees’ meat con­sump­tion is large­ly sea­son­al goes far toward explain­ing why human beings have always eat­en meat. Chim­panzees are most like­ly to eat meat dur­ing the time of year when they are los­ing weight because their usu­al foods are in rel­a­tive­ly short sup­ply. Peo­ple think of meat as a source of pro­tein, but it’s main­ly a source of calo­ries, espe­cial­ly from fat. Meat is also a good source of sodi­um, which is in rel­a­tive­ly short sup­ply in the chim­panzees’ fruit and veg­etable diet.

The fact that chim­panzees eat the most meat dur­ing times of food short­ages sug­gests that their food choic­es fol­low a pat­tern that biol­o­gists call opti­mal for­ag­ing the­o­ry. Ani­mals try to get the most calo­ries for the least effort and with­out get­ting hurt. Opti­mal for­ag­ing the­o­ry explains why chim­panzees eat meat but goril­las don’t, and why chim­panzees eat more meat dur­ing times of food short­age.

Chim­panzees are main­ly fruit eaters, but they also eat a lot of veg­eta­bles. The prob­lem with fruit is that it’s sea­son­al. Worse yet, a fruit tree rep­re­sents a rich enough source of calo­ries that ani­mals will fight over it. When fruit is scarce, chim­panzees can use the skills they devel­oped in fight­ing over the fruit to engage in preda­to­ry behav­ior. Also, chim­panzees are small enough and fast enough that they are rea­son­ably good hunters.

Goril­las, on the oth­er hand, main­ly eat leaves. There are gen­er­al­ly plen­ty of leaves to go around, and a leafy plant is gen­er­al­ly so poor in calo­ries that it’s not worth fight­ing to pro­tect. To sub­sist on leaves, how­ev­er, you have to eat an enor­mous vol­ume of food. Since leaves are so low in calo­ries, leaf-eaters have to be good at con­serv­ing their ener­gy. That’s why goril­las have such a placid dis­po­si­tion. For a goril­la, hunt­ing is sim­ply not worth the effort. They are too big and slow to catch very much, and they’re large enough that they’d risk injury if they got too reck­less.

Chim­panzees use twigs to fish for ter­mites, and goril­las don’t. Some peo­ple think that this fact means that chim­panzees are smarter than goril­las. I don’t. If you are a juve­nile goril­la or a preg­nant or nurs­ing female goril­la, you don’t need to mess around with a lit­tle bit­ty twig to get a few ter­mites. All you have to do is wait for the sil­ver­back to knock over a rot­ting tree. Then all of you can eat as many ter­mites as you’d like.

Some peo­ple have argued that the bal­ance between ani­mal and plant foods in a hunter-gath­er­er society’s diet rep­re­sents the opti­mal bal­ance for human nutri­tion. I think that’s idi­ot­ic. Hunter-gath­er­er peo­ples (or should I say, gath­er­er-hunter peo­ples) tend to fol­low opti­mal for­ag­ing the­o­ry just like any oth­er oppor­tunis­tic feed­er. Their goal is to sur­vive in the short term, not to avoid breast or prostate can­cer in mid­dle or old age. The main threat to their short-term sur­vival is star­va­tion.

Meat rep­re­sents a con­cen­trat­ed source of calo­ries. The fact that a rel­a­tive­ly high per­cent­age of these calo­ries comes from pro­tein is actu­al­ly a dis­ad­van­tage. Hunt­ing peo­ples pre­fer the fat­ti­est foods. Peo­ple who end up hav­ing to sub­sist on extreme­ly low-fat meat, such as rab­bit, are prone to a prob­lem called fat-hunger or rab­bit star­va­tion. This prob­lem prob­a­bly results from a diet that has too much pro­tein and not enough car­bo­hy­drate or fat. On a low-carb diet and dur­ing star­va­tion, the body has to make its sug­ar sup­ply out of pro­tein. Per­haps the body can make only so much sug­ar out of pro­tein. As long as you are eat­ing enough fat to meet most of your ener­gy needs, your body can make enough sug­ar out of pro­tein to feed your brain. If you were eat­ing pro­tein but not enough fat or carbs, you could end up in seri­ous trou­ble. So you could end up in trou­ble from a diet that is too high in pro­tein. In con­trast, it is prac­ti­cal­ly impos­si­ble to avoid get­ting enough pro­tein, as long as you are eat­ing enough unre­fined plant foods to get enough calo­ries.

Famine is not a sig­nif­i­cant cause of death in the Unit­ed States. In fact, peo­ple in the Unit­ed States are far more like­ly to die of the dis­eases of afflu­ence, such as heart dis­ease and can­cers of the breast and prostate. Ani­mal-based foods and fat­ty processed foods are the main con­tribut­ing caus­es of the dis­eases of afflu­ence. The abil­i­ty to use ani­mals for food may have helped human beings sur­vive to the mod­ern era, espe­cial­ly in the Arc­tic, but ani­mal-based foods are a major cause of death and dis­abil­i­ty in the Unit­ed States today. Think about that the next time you hear some­one pro­mot­ing a “Paleo” diet.

No, It’s a Low-Fat, High-Fiber Diet That Keeps Gorillas Lean!

A recent arti­cle in the New York Times argued that goril­las stay slim because they eat a high-pro­tein diet. While I’m glad to see some­one else point out that a plant-based diet pro­vides ade­quate amounts of pro­tein, I’m annoyed to see sci­en­tists and jour­nal­ists mis­un­der­stand and mis­rep­re­sent the real sig­nif­i­cance of this fact. It’s as if they haven’t read the basic lit­er­a­ture on nutri­tion and can’t under­stand arith­metic.

Yes, the gorilla’s nat­ur­al diet is high in pro­tein, as a per­cent­age of calo­ries. How­ev­er, the goril­las’ nat­ur­al food tends to be low in calo­ries, because the calo­ries are dilut­ed by water and fiber. Goril­las have to eat an enor­mous amount of food every day to get enough calo­ries. When human vol­un­teers tried to eat a goril­la-style diet for a short peri­od of time to see how it would affect their cho­les­terol lev­els, they had to spend more than 8 hours a day eat­ing, just to get enough calo­ries to keep from los­ing weight dur­ing the tri­al. Goril­las stay slim because of the high fiber con­tent and low fat con­tent of their food, not because of the bal­ance of pro­tein to car­bo­hy­drate in their food!

The biggest dietary chal­lenge for a goril­la, as for any leaf-eater, is to get enough calo­ries. When they eat a rel­a­tive­ly high-pro­tein diet, they just end up con­vert­ing the excess pro­tein to sug­ar and burn­ing it for ener­gy. Unfor­tu­nate­ly, pro­tein is “dirty sug­ar.” Burn­ing pro­tein for ener­gy pro­duces waste prod­ucts such as urea and sul­fu­ric acid.

Peo­ple can stay very slim on a high-car­bo­hy­drate diet, if it is also high in fiber and low in fat. For exam­ple, when Chris Voigt of the Wash­ing­ton State Pota­to Com­mis­sion decid­ed to go on a pota­to-only diet as a pub­lic­i­ty stunt, he fig­ured that he had to eat 20 pota­toes a day. In prac­tice, he found it real­ly hard to eat his entire pota­to ration, because pota­toes are so fill­ing. As a result, he lost a lot of weight. Even when he made an effort to eat his entire pota­to ration every day, he con­tin­ued to lose weight. That’s because a starchy diet improves insulin sen­si­tiv­i­ty and thus revs up your metab­o­lism. Peo­ple who eat starchy diets burn more calo­ries than peo­ple on fat­ty diets. Voigt lost 21 pounds dur­ing his 60-day pota­to diet. His cho­les­terol lev­els, triglyc­eride lev­els, and even his blood sug­ar lev­els decreased!

Accord­ing to the New York Times, Dr. Rauben­heimer claimed that mod­ern soci­eties “are dilut­ing the con­cen­tra­tion of pro­tein in the mod­ern diet. But we eat to get the same amount of pro­teins we need­ed before, and in so doing, we’re overeat­ing.” What non­sense!

Nutri­tion sci­en­tists have known for more than 100 years that human pro­tein needs are mod­est and are eas­i­ly met by any rea­son­able plant-based diet. Also, the soci­eties with the biggest prob­lem with obe­si­ty are also the ones with the high­est pro­tein intake! Mod­ern soci­eties are con­sum­ing too much fat and too lit­tle fiber. Ani­mal foods are a big offend­er, because they con­tain fat but no fiber and usu­al­ly no digestible car­bo­hy­drate. Refined foods are also a big offend­er, because they rep­re­sent the con­cen­trat­ed calo­ries from plants–with the fiber and oth­er whole­some things stripped out.

The take-home les­son from the goril­la sto­ry shouldn’t have been that peo­ple need to eat more pro­tein. It’s that peo­ple need to eat plants. If peo­ple don’t want to spend 8 hours a day eat­ing leafy veg­eta­bles, they can eat some nice, fill­ing pota­toes or oth­er starchy sta­ples along with plen­ty of veg­eta­bles and fruit.

We’re Making the Gorillas Sick! Stay Away From Them!

When I was a child, I saw that the goril­las, unlike all the oth­er ani­mals at the Colum­bus Zoo, were behind glass. My par­ents said that this was to keep the goril­las from catch­ing dis­eases like tuber­cu­lo­sis from the peo­ple who came to see them.

Goril­las look almost human because their genes are strik­ing­ly sim­i­lar to ours. Chim­panzees and bono­bos look even more human-like because their genes are even more like ours. The more DNA you have in com­mon, the more like­ly it is that you’ll be sus­cep­ti­ble to the same bac­te­ria and virus­es. Human beings prob­a­bly caught the first cas­es of AIDS from chim­panzees. Now there is a report from the U.S. Cen­ters for Dis­ease Con­trol and Pre­ven­tion that endan­gered wild goril­las are catch­ing a dead­ly virus from human beings! They are prob­a­bly catch­ing the dis­ease from the eco­tourists who go to see them!

On one hand, eco­tourism seems to be nec­es­sary to help pro­tect the goril­la habi­tat. On the oth­er hand, the dis­eases that the eco­tourists bring with them could be dead­ly to the goril­las.

Why Gorillas, Why Not Chimpanzees?

Many peo­ple have asked me, why do you ask where goril­las get their pro­tein, when our bod­ies and our body chem­istry more close­ly resem­ble those of chim­panzees? My answer is that goril­las are much big­ger and more pow­er­ful than chim­panzees. Last night, I saw a muse­um exhib­it that com­pared a goril­la skull to a chim­panzee skull and a human skull. (They might have been mod­els. It was hard to tell.) The goril­la skull was huge! The chim­panzee skull was about the same size as a human skull.

The oth­er rea­son is that goril­las eat a much more strict­ly plant-based diet. Chim­panzees hunt once in a while, and they often eat their kill. Even so, they still eat a lot less meat than just about any human pop­u­la­tion. Nev­er­the­less, I was afraid that the fact they eat a lit­tle bit of meat now and then would mud­dy the waters.

My point is this. Most of the real­ly big and pow­er­ful land ani­mals got big and pow­er­ful by eat­ing plants. They don’t wor­ry about get­ting a pro­tein defi­cien­cy on a plant-based diet, and nei­ther should you.


(Image cour­tesy of Mahla­ti­ni Lux­u­ry Safari, https://www.mahlatini.com/gorilla-trekking-safaris/)

Humans and Gorillas Can Get Gout, But We Can Both Get By With Very Little Salt!

Gouty arthri­tis results from the buildup of crys­tals of uric acid in the joints.

Peo­ple who eat a lot of meat are at risk for gout—one of the most painful con­di­tions known to med­ical sci­ence. Gout results when crys­tals of a uric acid salt build up in the joints. These crys­tals can also build up in the uri­nary sys­tem, pro­duc­ing kid­ney stones—another of the most painful con­di­tions known to med­ical sci­ence. A recent the­o­ry sug­gests that our high risk for gout is a side effect of an adap­ta­tion that enabled human beings, goril­las, and the oth­er great apes to sur­vive a short­age of sodi­um.

Although eat­ing meat and seafood caus­es gout in peo­ple, it doesn’t cause gout in a nat­ur­al car­ni­vore like a cat. That’s because cats, like most mam­mals, pro­duce an enzyme called uri­c­ase, which breaks uric acid down into some­thing that dis­solves eas­i­ly in water and pass­es right out through the kid­neys. Human beings and the great apes are prac­ti­cal­ly the only mam­mals that can’t make uri­c­ase. This fact sug­gests that peo­ple, like goril­las, should prob­a­bly be eat­ing a high­ly plant-based diet.

In the wild, apes are free from gout because their plant-based diet is low in purines, which the body con­verts to uric acid. Fruit and veg­eta­bles are also mild­ly alka­lin­iz­ing, and the mild meta­bol­ic alka­lo­sis enables the blood to keep more uric acid dis­solved. So the great apes can live gout-free even though they can’t make uri­c­ase. Sim­i­lar­ly, human beings can avoid gout sim­ply by eat­ing a plant-based diet with a heavy empha­sis on fruit and veg­eta­bles.

It’s sur­pris­ing that human beings and the great apes can’t make uri­c­ase. We’re prac­ti­cal­ly the only mam­mals that don’t. The gene for uri­c­ase has sur­vived almost unchanged through hun­dreds of mil­lions of years of evo­lu­tion. That’s gen­er­al­ly a sign that the gene does some­thing impor­tant. Yet the lack of uri­c­ase might actu­al­ly be an advan­tage for wild apes. The extra uric acid in their blood might enable them to sur­vive on a diet that would oth­er­wise be dan­ger­ous­ly low in sodi­um.

As we’ve seen, goril­las eat a very low-sodi­um diet. Meat-eaters don’t run a risk of sodi­um defi­cien­cy, because meat and oth­er ani­mal-based foods are high in sodi­um.

Where Do Gorillas Get Their Vitamin B12?

Termites: The Other, Other White Meat

Vit­a­min B12 is one of the two nutri­ents that are essen­tial for human beings but aren’t avail­able from a pure­ly plant-based diet. The oth­er is vit­a­min D, which isn’t tru­ly a vit­a­min but is a hor­mone that your body can make for itself if you get some bright sun­shine on your skin. Goril­las live in Africa, where there’s no short­age of sun­shine. The inter­est­ing ques­tion is where do they get their vit­a­min B12? Evi­dent­ly, they get it from the insects and oth­er creepy crawlies that they eat. Their favorites are termites—the oth­er, oth­er white meat.

As you can see, the goril­las just dis­man­tle the tree where the ter­mites are. That’s prob­a­bly why they don’t both­er using tools to fish for ter­mites, as chim­panzees do:

Except for vit­a­min D and vit­a­min B12, plants pro­vide all the essen­tial nutri­ents that peo­ple need. Plants con­tain min­er­als, such as cal­ci­um and iron, which they have absorbed from the soil. Plants con­tain all of the oth­er vit­a­mins and essen­tial amino acids, which they have made for their own pur­pos­es. Plants are also the orig­i­nal source of the essen­tial fat­ty acids. How­ev­er, plants don’t make vit­a­min B12, and nei­ther do ani­mals. All of the vit­a­min B12 in nature comes from bac­te­ria.

Some plant-eaters get their sup­ply of vit­a­min B12 from the bac­te­ria in their own diges­tive sys­tem, as long as they are eat­ing some­thing that con­tains the ele­ment cobalt. (Vit­a­min B12 con­tains cobalt). Cat­tle and sheep are par­tic­u­lar­ly good at get­ting vit­a­min B12 from their own gut bac­te­ria. They have a lot of bac­te­r­i­al fer­men­ta­tion going on in their stom­achs, so the vit­a­min B12 is made before the food pass­es through the part of the intes­tine where the vit­a­min B12 gets absorbed. Such ani­mals are called “foregut fer­menters.”

Oth­er species, includ­ing rab­bits and goril­las and human beings, are “hindgut fer­menters.” Their gut bac­te­ria make vit­a­min B12, but only after the food has passed through the part of the intes­tine where the vit­a­min B12 can get absorbed. Rab­bits solve this prob­lem by eat­ing some of their own drop­pings. Wild moun­tain goril­las some­times do the same thing, usu­al­ly dur­ing peri­ods of bad weath­er. Cap­tive goril­las do it a lot more often, pos­si­bly because they are bored.

On the oth­er hand, goril­las and human beings can eat foods that already con­tain ready-made vit­a­min B12. For goril­las, that means tasty, tasty ter­mites, which get vit­a­min B12 from their own gut bac­te­ria. Mod­ern human beings who don’t want to eat ter­mites, or any oth­er ani­mal prod­ucts, can get their vit­a­min B12 from a nice, clean, and very cheap sup­ple­ment. As long as their gas­troin­testi­nal sys­tem is healthy, peo­ple can even take their vit­a­min B12 by mouth. Vit­a­min B12 shots are use­ful for peo­ple who have trou­ble absorb­ing vit­a­min B12 from their food, because of gas­troin­testi­nal dis­ease.

How Gorillas Celebrate Christmas–With Brussels Sprouts!

Just Make Sure You Stay Upwind of Them

At Christ­mas­time last year, the Chess­ing­ton World of Adven­tures, in Sur­rey, Eng­land, gave their goril­las some Brus­sels sprouts. The goril­las loved them, but the after­ef­fects hor­ri­fied the zoo vis­i­tors.

Goril­la keep­er Michael Rozzi said: “We feed the goril­las Brus­sels sprouts dur­ing the win­ter because they are packed with vit­a­min C and have great nutri­tion­al ben­e­fits. Unfor­tu­nate­ly, an embar­rass­ing side effect is that it can cause bouts of flat­u­lence in humans and ani­mals alike. How­ev­er, I don’t think any of us were pre­pared for a smell that strong.” The goril­las didn’t seem to care, nor did any of the goril­las ask any­one to pull their fin­ger. The zoo keep­ers solved the prob­lem by giv­ing the goril­las their Brus­sels sprouts after clos­ing time. On Christ­mas Day, when the zoo was closed to the pub­lic, the goril­las got to eat Brus­sels sprouts all day long. It was a solu­tion that worked for every­one.

I eat a lot of Brus­sels sprouts in the win­ter, and I eat oth­er mem­bers of the cab­bage fam­i­ly and lots of beans year-round, but I nev­er have a gas prob­lem. I’m grate­ful for that, but it means I can’t use myself as a sub­ject to test pos­si­ble reme­dies. Some peo­ple rec­om­mend Bean-o, and oth­ers rec­om­mend spices and herbs such as cumin, fen­nel, car­away, dill, pep­per­mint, chamomile, sage, and thyme.

Many peo­ple who think that they hate Brus­sels sprouts real­ly only hate over­cooked Brus­sels sprouts. Over­cook­ing releas­es a stinky sul­fur com­pound called sin­i­grin. Try cook­ing your sprouts for only 6 to 7 min­utes, and see if that makes a dif­fer­ence. The sin­i­grin will stay put, until you digest the sprouts.

Sin­i­grin may stink, but it’s prob­a­bly good for you. It evi­dent­ly caus­es can­cer cells in the colon to com­mit sui­cide, which could help to explain why pop­u­la­tions that eat a lot of cab­bage and oth­er mem­bers of the Bras­si­ca fam­i­ly, includ­ing Brus­sels sprouts, have a low risk of colon can­cer.

Why Gorillas Are So Gentle

The Upside and Down­side of Liv­ing on Leaves

All of the great apes are plant-eaters. Even chim­panzees, which occa­sion­al­ly hunt and kill small ani­mals and eat them, still eat less meat than near­ly any human soci­ety. Yet the var­i­ous great ape species fit into dif­fer­ent eco­log­i­cal nich­es, so they focus on dif­fer­ent kinds of plant foods. Chim­panzees are main­ly fruit eaters. Although goril­las will eat fruit and nuts when­ev­er they’re avail­able, they main­ly eat leaves.

The fact that goril­las main­ly eat leaves explains a lot about their behav­ior and social struc­ture. Leaves don’t run away, so there’s no need to chase them. Leaves are so abun­dant in the gorilla’s habi­tat, and so low in calo­ries, that it’s point­less to fight over them. A tree full of ripe fruit or nuts is anoth­er mat­ter, entire­ly. In gen­er­al, I’d expect ani­mals that main­ly eat leaves to be nicer than ani­mals that main­ly eat fruit, because they have less to fight over.

Goril­las face the same kinds of chal­lenges as any ani­mal that spe­cial­izes in eat­ing leaves. Here are a few of those chal­lenges, as explained by Fiona Sun­quist (The strange, dan­ger­ous world of folivory. Inter­na­tion­al Wildlife; Jan­u­ary-Feb­ru­ary, 1991; pages 4–10):
The demands of liv­ing on low-ener­gy and often poi­so­nous food means that most foli­vores live close to the lim­it of their ener­gy sup­ply.
  • They must con­serve ener­gy wher­ev­er pos­si­ble, and this often trans­lates into being very slow.
  • It is no coin­ci­dence that the sloth, the world’s slow­est mam­mal, is a foli­vore.
  • Besides being slow, foli­vores also spend much of their time rest­ing.


All this sug­gests that if you want to be a marathon run­ner, you’ll want to eat some­thing besides leaves–ideally some­thing starchy. If you sim­ply want to be thin­ner, you might want to try eat­ing more leaves.