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Why do mountain gorilla eat just 1.7% fruit, while lowland gorillas eat 25%?

Why do mountain gorilla eat just 1.7% fruit, while lowland gorillas eat 25%?


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Eastern lowland gorillas have more diverse diets, which vary seasonally. Leaves and pith are commonly eaten, but fruits can make up as much as 25% of their diets. https://en.wikipedia.org/wiki/Gorilla#Food_and_foraging


The mountain gorilla is primarily a herbivore; the majority of its diet is composed of the leaves, shoots and stems (85.8%) of 142 plant species. It also feeds on bark (6.9%), roots (3.3%), flowers (2.3%), and fruit (1.7%) https://en.wikipedia.org/wiki/Mountain_gorilla#Habitat_and_ecology


Mountain plants have to be hardy, especially if they grow above the frost line. They are more likely to be tough vegetation (leaves, shoots, and stems) as mentioned in the mountain gorilla diet.

The lowlands have much more plant diversity (and generally better food). Sweet fruits have better calories for the effort required to forage and digest them, so you would expect the lowland gorillas to prefer fruit.


Food-Associated Calling in Gorillas (Gorilla g. gorilla) in the Wild

Many nonhuman primates produce food-associated vocalizations upon encountering or ingesting particular food. Concerning the great apes, only food-associated vocalizations of chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) have been studied in detail, providing evidence that these vocalizations can be produced flexibly in relation to a variety of factors, such as the quantity and quality of food and/or the type of audience. Only anecdotal evidence exists of eastern (Gorilla beringei) and western gorillas (Gorilla gorilla) producing food-associated vocalizations, termed singing or humming . To enable a better understanding of the context in which these calls are produced, we investigated and compared the vocal behavior of two free-ranging groups of western lowland gorillas (Gorilla g. gorilla) at Mondika, Republic of Congo. Our results show that (a) food-associated call production occurs only during feeding and not in other contexts (b) calling is not uniformly distributed across age and sex classes (c) calls are only produced during feeding on specific foods and (d) normally just one individual gives calls during group feeding sessions, however, certain food types elicit simultaneous calling of two or more individuals. Our findings provide new insight into the vocal abilities of gorillas but also carry larger implications for questions concerning vocal variability among the great apes. Food-associated calls of nonhuman primates have been shown to be flexible in terms of when they are used and who they are directed at, making them interesting vocalizations from the viewpoint of language evolution. Food-associated vocalizations in great apes can offer new opportunities to investigate the phylogenetic development of vocal communication within the primate lineage and can possibly contribute novel insights into the origins of human language.

Citation: Luef EM, Breuer T, Pika S (2016) Food-Associated Calling in Gorillas (Gorilla g. gorilla) in the Wild. PLoS ONE 11(2): e0144197. https://doi.org/10.1371/journal.pone.0144197

Editor: Katie Elizabeth Slocombe, University of York, UNITED KINGDOM

Received: August 4, 2015 Accepted: November 13, 2015 Published: February 24, 2016

Copyright: © 2016 Luef et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: The data underlying the findings of this study are available from the institutional server of the Max-Planck Institute for Ornithology, Seewiesen (Germany) following the link: http://edmond.mpdl.mpg.de/imeji/collection/s1PVeZMnznMV2m0.

Funding: This work was supported by Alexander von Humboldt Stiftung (Germany), Simone Pika, Grant Number: Sofja-Kovalevskaja-Award 2010–2015, https://www.humboldt-foundation.de/web/start.html and Fritz-Thyssen Stiftung (Germany), Eva Maria Luef, 2012, http://www.fritz-thyssen-stiftung.de/. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.


Why do mountain gorilla eat just 1.7% fruit, while lowland gorillas eat 25%? - Biology

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Health problems disappear when captive gorillas fed wild diet

Posted by John on February 23rd, 2011 | 47 Comments

Watch this video. Then re-blog it, like it on facebook, and re-tweet it. Tell your family and send it to your doctor. Write a letter to your congressman. Show it to your niece and nephew, and teach it in your classroom. Let your dog sniff the computer while it's playing. Meditate on it. Put it on a thumb drive, duct tape it to a brick, and throw it through the window at the USDA. Put it in a time capsule so future generations will know. Convert it into binary and beam it into space.

And here's the article: Captive Gorillas Succumbing to Human Disease. I'm just going to post it here without commentary, just my bolding.

Life for humans is much easier than for animals in the wild. On a day-to-day basis, we generally do not have to worry about being eaten or starving to death. Depending on the individual's job, some can get by just fine by sitting around all day. However, this lifestyle brings forth its own set of health issues such as diabetes and heart disease, illnesses rarely found in the wild. These "human" diseases have spread to gorillas that are raised in captivity.

The only species of gorilla kept at North American zoos is the Western Lowland Gorilla. The number one killer of males in captivity is heart disease, much like humans. After a 21 year old gorilla named Brooks died of heart failure at Cleveland Metroparks Zoo in 2005, a group of researchers decided to examine how the gorilla&rsquos lifestyle affect their health. The team was led by Elena Hoellein Less, a PhD candidate in biology at Case Western Reserve University.

The researchers believe that heart disease can be stopped by switching captive gorillas back to their natural diets in the wild. For decades, zoos have fed gorillas bucket loads of high vitamin, high sugar, and high starch foods to make sure their got all their nutrients. At the Cleveland zoo, they have started feeding food such as romaine lettuce, dandelion greens, endives, alfalfa, green beans, flax seeds, and even tree branches which they strip of bark and leaves. To top it off, they give the gorillas three Centrum Silver multivitamins inside half a banana.

Going back to this natural diet has changed gorilla behavior. Before, gorillas only ate during a quarter of their day because the food was so packed with nutrients. Now at Cleveland, they spend 50-60 percent of their day eating which is the same amount as in the wild. With all this extra eating, the gorillas have doubled their caloric intake, yet at the same time have dropped 65 pounds each. This brings their weight more in line with their wild relatives.

"We're beginning to understand we may have a lot of overweight gorillas," said Kristen Lukas, an adjunct assistant professor of biology at Case Western Reserve and chair of the Gorilla Species Survival Plan®. "And, we're just recognizing that surviving on a diet and being healthy on a diet are different. We've raised our standards and are asking, are they in the best condition to not only survive but to thrive?"

Less and her crew are continuing their studies of captive gorillas by measuring the fat on their backs to create a gorilla body mass index. This can be used to gauge healthy weight for gorillas much as it is used for humans. The next step, says Less, is to exercise gorillas at the zoo to get their muscles to a similar level as their wild relatives.

I may shut down the blog after this post because there's nothing left to say.

Thank you to Mark for the link.

47 Responses to “Health problems disappear when captive gorillas fed wild diet”

OUTSTANDING! The ancestral diet, good for a critter?!

I love that you are emphasizing the similarities between us and the animals we force-feed an unnatural diet. The significant implication, of course, is that we are animals too. That one very simple point is perhaps why so many people shrug off paleo as a fad — they are so deeply entrenched in conventional thinking that they can’t even accept that they are a part of nature. The emphasis you’ve been making lately might be the important first step in moving away from that.

HUMANS ARE NOT ANIMALS, THEY ARE HUMANS

Strangely enough I hear pretty much that refrain all the time. "We have evolved past the point where we should be dependent upon nature [i.e. evolution] to survive." For a long time, when I was a vegan, something close to that was my mantra – that from a cruelty-to-animals/waste standpoint, the vegan lifestyle was our response to the cruel and wasteful path that nature designed for us. This new, fabricated food and exercise regimen was somehow better than what our ancestors had!

Clearly I should have done my research on that one, I know… but you see how very easy it is to fall into that logical trap. Pretty silly.

Kingdom: Animalia
Class: Mammalia

Sounds like an animal to me.

Yep. Lots pet owners will share the same story. Feed a dog what it’s supposed to eat and a whole host of problems (physical and behavioral) will disappear. It was such a no brainer when we switched our dogs to raw that I honestly felt like a dolt when I discovered "paleo" (years later!) and was like: oh yeah…I guess a species appropriate /ancestral diet makes sense for humans too!

I have noticed a lot of talk here lately about animals. You might be interested by this article which is also off the beaten path but very much connected to the same themes:

The principle underlying most memory techniques is that our brains don&rsquot remember every type of information equally well. Like every other one of our biological faculties, our memories evolved through a process of natural selection in an environment that was quite different from the one we live in today. And much as our taste for sugar and fat may have served us well in a world of scarce nutrition but is maladaptive in a world of ubiquitous fast-food joints, our memories aren&rsquot perfectly suited for our contemporary information age.

Thanks, Miles, this is cool

I really enjoyed that article, thanks for posting it.

I really enjoyed that article, thanks for posting it.

Gorilla body mass index. Uh oh, I better get my back shaved…

"And, we’re just recognizing that surviving on a diet and being healthy on a diet are different."

LOVE this quote from the article! Thanks for sharing the video.

it was madness to ever think that gorillas would thrive on a diet of starchy vegetables. glad to see the ‘paleo’ philosophy is spreading to zoos and i have no doubt these gorillas will be much healthier and happier on their natural diet of romaine lettice and Centrum Silver Multivitamin pills, just like they would eat in the wild

jelly beans and marshmallows…terrible

What, it doesn’t work for you? I tend more towards a skittle diet, but she, I, and almost everyone I know have been reaping the benefits of comfort eating sugar, getting no social interaction other than that which is based upon junk food, and never getting any exercise. (Yeah–so terrible on so many levels.) Also, on a kind of related note- a while back I was investigating what causes regurgitation and reingestion in primates in captivity after watching it for several painful but fascinating hours at San Diego Zoo bonobo habitat–it’s crazy to watch someone induce vomiting and eat it on an endless loop with horrified moms shielding thier kids eyes all around–and I discovered that, at least in 1997, the Milwaukee Zoo used Kool-Aid, sugar-free Jello, chewing gum, cookies and cereal as part of thier bonobo behavior enrichment program (coincidentally in the same study: http://www.nagonline.net/HUSBANDRY/Diets%20pdf/Bonobo%20Nutrition.pdf they also reported weight problems in some of the animals) and Cincinnati was regularly giving them chips, pretzels, party mix (WHOO!), spaghetti and tons more puzzling and on the level of jelly bean gross things. So you posting this made me feel a tiny bit better about zoo dieticians–I was seriously wondering if they forgot they were working with animals after looking into the R&R stuff. Kind of like human dieticians, too, I suppose.

unbelievable, thanks for the link

Monkeys, humans, and pets all getting modern diseases consuming modern diets of over processed dreck. When will we ever learn.

Another article in the NYT this week talked about studies showing that sedentary, junk food-fed monkeys have similar poor health outcomes to humans. http://bit.ly/hopWCH

There are so many awesome things going on in this article that you are right, John, you may need to call this the end. Pack up and go home, it’s done.

But you missed the most the most awesome part. Just in case, especially men, need some more convincing on the success behind Paleo diet…all the women advocating it in this video are are not just well-spoken but also really cute.

One day we’ll realize that we can’t outsmart God when it comes to creating and/or sustaining life wether it be in procreation/artificial inteligence or the mere food we eat. Life force can not be created, it is merely recycled. Our hubris has taken us beyond this intuitive truth and led us to think we can think up life force in chem labs across the world.

Whats the difference between cooking a steak and working with chemicals or genetics in a lab? Its all chemistry and change.

In a theoretical sense, you’re right — everything is just “chemicals”. But they’ve been trying to formulate breast milk for over a hundred years now and still can’t do it as well as mother nature.

I had a high school chemistry teacher who had a Ph.d. in organic chemistry. We were once talking about spider silk and how much stronger it was than any man-made material (or at least steel or something). I asked why we didn’t just manufacture spider silk if that was the case. He pointed out that the molecular structure of spider silk is pretty complicated, and to make it you’d have to be able place specific atoms in specific places in molecule after molecule–in fact trillions of molecules. He said that’s the power of life itself. If you could do that, you could make DNA, or an entire genome. Our science is just not there yet. While breast milk is an unremarkable, everyday little feat of nature, it is quite simply beyond our meager ability to replicate, even with all our science.

A steak was once walking around eating grass that takes life source from the sun and nutrients from the soil that gets fertilized with dead bugs that came from some stagnant pond that was provided oxygen by some unicellular algae…..could go all the way back to the Big Bang if you’d like. Lab chemicals have no life. Sure this whole universe was once only mostly Hydrogen at one point but if you use that as your argument, we have to get in to a theology discussion.

This is great! I was always skeptical of popping pills. My family’s business was with performance dogs and we also had a small farm. Diet was a major factor and if something was wrong with any of our animals the first place we looked was diet. You never go get a prescription to give the animal, the rest of it’s life, in order to correct the problem. We always corrected the diet. So I always wondered why the same principle didn’t apply to me. When I came across the Paleo diet 6 or 7 years ago it just made complete sense to me. I’m just now getting around to making the change in my lifestyle, it was a hard battle for me to overcome my "addiction" and issues with food. I’ve been strictly Paleo since January 3rd and I know that I’ve now experienced clean, proper living and it’s given me the ability to be true to myself. Wonderful link and I’ve shared with my friends and made my parents watch it. Hopefully it will get them thinking about changing their lifestyle.

Thanks for sharing the link. Good work on going full-on paleo — stick with it.

A question on their un-natural diet, did it contain PUF- 6 oils?

Don’t know, but I’ll try to find out

"So if you think that keeping a gorilla in a cage with insufficient fresh air and exercise and feeding it a diet that’s going to make it fat, sick, and ultimately kill it is wrong and cruel, why do that to yourself?"

I live in Cleveland and have seen the gorillas in question. Just last year I asked my wife why they looked so unhappy, just lying there, staring at the sky. I swear for all the world they looked like "Mojo" in that Simpsons episode where Homer’s helper monkey eats, drinks, and smokes too much.

But scientists and academics are our betters, and we should do what they say, always.

Ahh, you’ve actually seen them — very cool. I will pray for Mojo.

But of course they are thriving when their diet is correct. Just like humans.

You know the vegans will use this as propaganda to claim that humans should also eat a solely plant-based diet, since the gorilla lost all this weight eating only shrubbery.

I hope they do, because that’s an easy one to refute

Propaganda? ….and…..the vegans will be right. Humans don’t NEED to eat the flesh of animals OR NEED to consume the milk of another species mammary glands. The PROOF is everywhere. One just need search the internet for Vegan blogs and info supporting Veganism. Far outweighs the anti-vegan info. A healthy whole foods Vegan diet is all the nutrition you need. Proof is in the pudding(vegan that is). I grew two superbly healthy babies in my womb meanwhile exercising at HIGH intensity 6-7 days a week and working 50 hours/week out of the home. Hah, propaganda. Your taste buds do not supercede the right of life for another animal. Vegan For Life! Go Vegan!

Seriously, what are you hoping to accomplish here? There are other platforms for this discussion. Stop wasting your time and ours.

And Melissa McEwen’s Smug Vegan Troll Comment Generator strikes again!

Oh no… please don’t tell me I just reponded to a bot…. AGHHH hahahah

@alhaddin: to be honest, I’m not entirely sure it was a bot, but it sure sounded like Melissa’s comment generator, which is a testament either to the quality of the bot or the lack of originality of the poster, I’m not sure which :).

@fearsclave I love Melissa’s vegan comment generator. Just so funny.
@alhaddin Thanks for sharing your experience with veganism in such a reasonable way

Sorry, perhaps that was a bit heavy-handed. Let me take a crack at a more measured response.

I used to be a vegan. For ten years, actually. The angle that I took on my choice of dietary regimen was very similar to the one which you are espousing here, including the proof which you believe is available all across the internet, as well as other places. I don’t disagree that that information is valid, but now I have chosen to draw a slightly more realistic and measure conclusion from it. We understand the horror that many vegans espouse about the factory farming of livestock and fish that prevails in this country and most of the westernized world. I understand that there is such a thing as the trophic hierarchy, aka food chain, which leaves the energy transfer from one level to the next grossly unequal, i.e. it is total insanity to rape the land to raise corn which we then transport all around the country to feed livestock which eat that and other disgustingly processed feed and then are transported all over again from slaughterhouse to packing facility to retailers to our fridges in a cycle of hopelessly wasteful energy consumption and inefficiency. We understand that the level of suffering and cruelty which prevails in this carnivory-industrial complex of ours is truly horrifying and largely unnecessary. We understand that, as silly as it sounds, cow farts are destroying the ozone layer more than aerosol hairspray. And we understand that, when an animal is pent up for years of its life and then slaughtered in a noisy and stark industrial facility, there are stress hormones and chemicals that leak into its muscles which we then ingest and absorb into our own bodies. All of that stuff is, unequivocally, very very bad, and one would be crazy to support its propagation. Fortunately, ALL of these problems are solved when one eats a diet that is based upon locally and ethically sourced foods, including pastured and/or grass-fed and -finished meat & fowl, and wild-caught fish. From an ethical and environmental standpoint dairy is hardly questionable under these criteria, but I concede that, from a strictly dietary standpoint the practice of consuming substances from another animal’s mammary glands is still largely up for discussion.

Your point about being healthy and fit as a vegan is, to me, anecdotal and extremely subjective, and therefore not really reliable as a benchmark for any other vegans except for yourself. (Raising children Vegan is, in my opinion, about as draconian as raising them Amish, but this is admittedly not my choice nor ultimately my judgment call to make.) That being said, I feel that it’s necessary to share my own experience with veganism here, because I think it sheds light on the duality of perceived vs. real profiles of personal health. During my time as a vegan, which spanned the critical growth period of my late adolescence, I thought of myself as being healthy because I was able to keep myself within (what I believed then to be) a desirable weight range in reality I was drastically underweight, had brittle bones, was unable to build any significant muscle mass (kind of a bad sign for a male during a time when he’s supposed to be flooded with testosterone). In additon to all of this I was unusually tired and hungry all the time due to disastrously low insulin sensitivity which was confirmed by not one but two endocrinologists who advised me to change my diet unless I wanted to become a type-2 diabetic in my late teens (admittedly, diabetes does "run in my family," but this is easily preventable with the right kind of diet). As soon as I switched over to a paleo mode of eating (compliant, of course, with all of the ethical specifications I delinated above), all of these problems went away within a matter of weeks. No kidding. It was only after ten years of thinking I was healthy in one mode of existence that I finally discovered how skewed that perception was – no doubt the result of my "buying in" to the idea that peak health could either be swapped out for (or dubiously achieved while) living as a complete herbivore.

One last point: don’t ever assume that we live and eat this way because our taste buds dictate it. There are days when my taste buds – whose demands are notoriously out of synch with what our bodies actually need – are clamoring for a double-chocolate fudge brownie, which, as I’m sure you are aware, can be made with fully vegan ingredients. Fortunately, like anyone else who is interested in reaching optimal health, I have learned to recognize that I’ve been conditioned by more than two decades of addiction to crap foods, and I’m not about to give in just because of a simple Pavlovian response.

This is probably more than you wanted to hear on this subject, so I’ll give it a rest. I will only say that I am sure that if you ask any other frequent reader on this site, they’ll be able to give you even more good reason for why we live the way we do (and they will be able to do so probably more eloquently, and more seamlessly, than I have done here).

Thanks for responding. I am not a bot or troll. I came across this site because someone at my Crossfit Gym linked the above article on our gyms site. I am glad I visited as I had heard of this study and hadn’t found an article yet, so I was pleasantly surprised to finally get my hands on a bit about it. I was not raised vegan! I was once a full on meat eater and milk chugger. I was raised that way and aggressively opposed vegetarians and vegans I came across in college. I also tried vegetarian as a teenager (about 17 yrs ago) after reading The Jungle (a book about the meat packing industry turn of the century) and largely lived on pasta, breads, and "healthy snack foods". If you don’t mind I’m going to make an assumption… As a teenager I highly doubt you were eating a well balanced diet consisting of a wide variety of fruits, vegetables, nuts, seeds and legumes. Was everyone in your family on the Vegan diet and accomodating your nutritional needs? Were you buying and preparing your own whole food nutrient dense and calorie filled meals? As a teenager I highly doubt that you were seeking out the healthiest options or have sufficient knowledge to create wholesome meals for yourself…or maybe you did…only you know. As a teenager, I certainly did NOT. Or did your eating habits more closely resemble the vegan version of the Standard American Diet? I can tell you from experience and education, any diet consisting of highly processed food, vegan or not, is going to FAIL. Most people who fail on the vegan diet do so because they are not eating a wide variety of WHOLE foods. Junk food veganism is no better and just as nutritionally void as SAD. I was also Strict Paleo for a full year before transitioning back to vegan. I had great success, but I found after taking out the processed foods in my diet and having gained significant experience with planning nutrient dense plant strong meals I also did not need the animal products. I just replaced those animal derived micro and macro nutrients with more WHOLE plant foods. Success:) There are well known endurance and strength athletes proving that a body can be plant strong. If you are interested here are a few: Bodybuilder Robert Cheeke, Endurance athlete Scott Jurek, NBA star John Salley, mountain runner Tim VanOrden, triathlete Rich Roll, Tour de France cyclist Dave Zabriskie and so many more. Have a great day.

You have an excellent point, which is that as a vegetarian/vegan it is incredibly easy to eat a very nutritionally poor diet. You’re correct that this was largely my experience (for all but the last year or so of my period of veganism), and I respect you for being able to find a level of fitness and health that works for you while on a vegan diet. However, to use your own line, the proof is in the pudding: there are tons and tons of vegans and vegetarians, possibly even the majority of those who identify as such, who subsist on a diet that is nutritionally godawful. I would challenge you to find even a single percentage-point’s worth of paleo folks whose diets are as nutritionally poor, because it is almost impossible to eat a nutritionally poor paleo diet. The fact that you must stay within a very narrow range of foods ("whole" or not) is not a good sign for the viability of your diet. We are beings built on variety and adaptation: Veganism largely excludes the former and exacts too much from our bodies via the latter.

Oh definitely and without a doubt a great number of veg*ns eat nutritionally poor diets. Absolutely. However, your argument is based on a snapshot in time of healthy committed Paleo enthusiasts vs. lazy junk food Vegans. These two experiences are not at the same level of potential. More accurately, if you take a snapshot of healthy committed Paleo enthusiasts vs. healthy whole plant foods Vegan enthusiasts, you have a more even playing field from which to draw conclusions. As much as my own process to veganism was laden with vegan junk foods, dairy and tofu filled vegetarianism, and low fat raw experimentations, I eventually struck a vegan balance that worked for me. For many it is a similar journey. So it is with Paleo I see people fall off all the time. I am surrounded by my fellow gym friends who attempt Paleo (it is part of Crossfit culture) and just can’t keep it up. However, I don’t doubt at all that if they keep getting back up they too will eventually strike a balance with their greatest Paleo potential. Veg*nism, Paleo, Vegetarian…one can fail or succeed with any one of these approaches. It takes committment and persistence. Each of these can succeed when processed junk is taken out and a variety of vegetables put in its place. That is the breaker in terms of sustainable health, the junk. Lastly, variety is absolutely not a problem in an herbivore diet. Not at all. I just can’t state that enough. If one lives near a major grocer and/or farmers markets/stands fruit, veggie, and legume variety is very high. One simply visit a grocer or market farm to witness variety in the hundreds of items. Nuts and seeds…I have well over a dozen different kinds in my kitchen right now. The number of Vegan-gluten free recipe blogs out there is insane. So many resources. Have a good one and Happy Eating!


Eastern Gorilla Interesting Facts

What type of animal is an Eastern Gorilla?

The Eastern Gorilla is the largest living primate and a critically endangered species of the gorilla subspecies. There are two Eastern Gorilla subspecies - Eastern Lowland Gorillas and Eastern Mountain Gorillas.

What class of animal does an Eastern Gorilla belong to?

The Eastern Gorilla belongs to the Mammalia class of the Animalia kingdom.

How many Eastern Gorillas are there in the world?

Eastern Gorillas are critically endangered species according to the IUCN Red List and their overall population is estimated to be somewhere around 5,000.

Where does an Eastern Gorilla live?

Eastern Gorillas are found in tropical moist forests, subalpine forests, and mountain rainforests of Sub-Saharan Africa.

What is an Eastern Gorilla's habitat?

The Eastern Gorilla's habitat includes Sub-Saharan African countries such as the subalpine forests and mountain rainforests of Rwanda, southwestern Uganda, and the eastern Democratic Republic of Congo. The Grauer gorilla inhabits forests along the Albertine Rift in the eastern Democratic Republic of Congo.

Who do Eastern Gorillas live with?

Eastern Gorillas are social creatures and they live in groups or social units called harems. The groups are often interconnected and have 35-40 members each.

How long does an Eastern Gorilla live?

Eastern Gorillas have an average lifespan of 30-60 years.

How do they reproduce?

Eastern Gorillas live in family groups that are led by a silverback male. The gorillas are polygamous in nature and the adult dominant male leader has the sole right to mate with all the females of its group. The animal species mate throughout the year and the females give birth to single baby gorillas each. The gestation period is about eight and a half months, and the females breastfeed and take care of the young gorillas for up to three years. Females attain their sexual maturity by 10 years of age, while males take 15 years to reach sexual maturity.

What is their conservation status?

Eastern Lowland Gorillas are an endangered species and are at risk of extinction. Conservation efforts have taken place and national parks set up to conserve these great apes. But illegal poaching and encroachment of their habitat continue to be the primary threat and their numbers are in constant decline. At present, there are about 5,000 individuals and the IUCN Red List classifies Eastern Gorillas as Critically Endangered (CE) species.


Contents

The word "gorilla" comes from the history of Hanno the Navigator (c. 500 BC), a Carthaginian explorer on an expedition to the west African coast to the area that later became Sierra Leone. [5] [6] Members of the expedition encountered "savage people, the greater part of whom were women, whose bodies were hairy, and whom our interpreters called Gorillae". [7] [8] It is unknown whether what the explorers encountered were what we now call gorillas, another species of ape or monkeys, or humans. [9] Skins of gorillai women, brought back by Hanno, are reputed to have been kept at Carthage until Rome destroyed the city 350 years later at the end of the Punic Wars, 146 BC.

The American physician and missionary Thomas Staughton Savage and naturalist Jeffries Wyman first described the western gorilla (they called it Troglodytes gorilla) in 1847 from specimens obtained in Liberia. [10] The name was derived from Ancient Greek Γόριλλαι (gorillai) 'tribe of hairy women', [11] described by Hanno.

The closest relatives of gorillas are the other two Homininae genera, chimpanzees and humans, all of them having diverged from a common ancestor about 7 million years ago. [12] Human gene sequences differ only 1.6% on average from the sequences of corresponding gorilla genes, but there is further difference in how many copies each gene has. [13] Until recently, gorillas were considered to be a single species, with three subspecies: the western lowland gorilla, the eastern lowland gorilla and the mountain gorilla. [9] [14] There is now agreement that there are two species, each with two subspecies. More recently, a third subspecies has been claimed to exist in one of the species. The separate species and subspecies developed from a single type of gorilla during the Ice Age, when their forest habitats shrank and became isolated from each other. [1]

Primatologists continue to explore the relationships between various gorilla populations. [9] The species and subspecies listed here are the ones upon which most scientists agree. [15]

    Genus Gorilla
      (G. gorilla)
        (G. g. gorilla) (G. g. diehli)
        (G. b. beringei) (G. b. graueri)

      chimpanzees (genus Pan)

      gorillas (genus Gorilla)

      orangutans (genus Pongo)

      gibbons (family Hylobatidae)

      The proposed third subspecies of Gorilla beringei, which has not yet received a trinomen, is the Bwindi population of the mountain gorilla, sometimes called the Bwindi gorilla.

      Some variations that distinguish the classifications of gorilla include varying density, size, hair colour, length, culture, and facial widths. [1] Population genetics of the lowland gorillas suggest that the western and eastern lowland populations diverged

      Gorillas move around by knuckle-walking, although they sometimes walk upright for short distances, typically while carrying food or in defensive situations. [19] A 2018 study investigating the hand posture of 77 mountain gorillas at Bwindi Impenetrable National Park (8% of the population) found that knuckle walking was done only 60% of the time, and they also supported their weight on their fists, the backs of their hands/feet, and on their palms/soles (with the digits flexed). Such a range of hand postures was previously thought to have been used by only orangutans. [20] Studies of gorilla handedness have yielded varying results, with some arguing for no preference for either hand, and others right-hand dominance for the general population. [21]

      Wild male gorillas weigh 136 to 227 kg (300 to 500 lb), while adult females weigh 68–113 kg (150–250 lb). [22] [23] Adult males are 1.4 to 1.8 m (4 ft 7 in to 5 ft 11 in) tall, with an arm span that stretches from 2.3 to 2.6 m (7 ft 7 in to 8 ft 6 in). Female gorillas are shorter at 1.25 to 1.5 m (4 ft 1 in to 4 ft 11 in), with smaller arm spans. [24] [25] [26] [27] Groves (1970) calculated the average weight of 42 wild adult male gorillas at 144 kg, while Smith and Jungers (1997) found the average weight of 19 wild adult male gorillas to be 169 kg. [28] [29] Adult male gorillas are known as silverbacks due to the characteristic silver hair on their backs reaching to the hips. The tallest gorilla recorded was a 1.95 m (6 ft 5 in) silverback with an arm span of 2.7 m (8 ft 10 in), a chest of 1.98 m (6 ft 6 in), and a weight of 219 kg (483 lb), shot in Alimbongo, northern Kivu in May 1938. [27] The heaviest gorilla recorded was a 1.83 m (6 ft 0 in) silverback shot in Ambam, Cameroon, which weighed 267 kg (589 lb). [27] Males in captivity can be overweight and reach weights up to 310 kg (683 lb). [27]

      The eastern gorilla is more darkly coloured than the western gorilla, with the mountain gorilla being the darkest of all. The mountain gorilla also has the thickest hair. The western lowland gorilla can be brown or greyish with a reddish forehead. In addition, gorillas that live in lowland forest are more slender and agile than the more bulky mountain gorillas. The eastern gorilla also has a longer face and broader chest than the western gorilla. [30] Like humans, gorillas have individual fingerprints. [31] [32] Their eye colour is dark brown, framed by a black ring around the iris. Gorilla facial structure is described as mandibular prognathism, that is, the mandible protrudes farther out than the maxilla. Adult males also have a prominent sagittal crest.

      Studies have shown gorilla blood is not reactive to anti-A and anti-B monoclonal antibodies, which would, in humans, indicate type O blood. Due to novel sequences, though, it is different enough to not conform with the human ABO blood group system, into which the other great apes fit. [33]

      A gorilla's lifespan is normally between 35 and 40 years, although zoo gorillas may live for 50 years or more. Colo, a female western gorilla at the Columbus Zoo and Aquarium, was the oldest known gorilla at 60 years of age when she died on 17 January 2017. [34]

      Gorillas have a patchy distribution. The range of the two species is separated by the Congo River and its tributaries. The western gorilla lives in west central Africa, while the eastern gorilla lives in east central Africa. Between the species, and even within the species, gorillas live in a variety of habitats and elevations. Gorilla habitat ranges from montane forest to swampland. Eastern gorillas inhabit montane and submontane forest between 650 and 4,000 m (2,130 and 13,120 ft) above sea level. [35] Mountain gorillas live in montane forest at the higher end of the elevation range, while eastern lowland gorillas live in submontane forest at the lower end. In addition, eastern lowland gorillas live in montane bamboo forest, as well as lowland forest ranging from 600–3,308 m (1,969–10,853 ft) in elevation. [36] Western gorillas live in both lowland swamp forest and montane forest, at elevations ranging from sea level to 1,600 m (5,200 ft). [35] Western lowland gorillas live in swamp and lowland forest ranging up to 1,600 m (5,200 ft), and Cross River gorillas live in low-lying and submontane forest ranging from 150–1,600 m (490–5,250 ft).

      Nesting

      Gorillas construct nests for daytime and night use. Nests tend to be simple aggregations of branches and leaves about 2 to 5 ft (0.61 to 1.52 m) in diameter and are constructed by individuals. Gorillas, unlike chimpanzees or orangutans, tend to sleep in nests on the ground. The young nest with their mothers, but construct nests after three years of age, initially close to those of their mothers. [37] Gorilla nests are distributed arbitrarily and use of tree species for site and construction appears to be opportunistic. [38] Nest-building by great apes is now considered to be not just animal architecture, but as an important instance of tool use. [38]

      A gorilla's day is divided between rest periods and travel or feeding periods. Diets differ between and within species. Mountain gorillas mostly eat foliage, such as leaves, stems, pith, and shoots, while fruit makes up a very small part of their diets. [39] Mountain gorilla food is widely distributed and neither individuals nor groups have to compete with one another. Their home ranges vary from 3 to 15 km 2 (1.16 to 5.79 mi 2 ), and their movements range around 500 m (0.31 mi) or less on an average day. [39] Despite eating a few species in each habitat, mountain gorillas have flexible diets and can live in a variety of habitats. [39]

      Eastern lowland gorillas have more diverse diets, which vary seasonally. Leaves and pith are commonly eaten, but fruits can make up as much as 25% of their diets. Since fruit is less available, lowland gorillas must travel farther each day, and their home ranges vary from 2.7 to 6.5 km 2 (1.04 to 2.51 mi 2 ), with day ranges 154–2,280 m (0.096–1.417 mi). Eastern lowland gorillas will also eat insects, preferably ants. [40] Western lowland gorillas depend on fruits more than the others and they are more dispersed across their range. [41] They travel even farther than the other gorilla subspecies, at 1,105 m (0.687 mi) per day on average, and have larger home ranges of 7–14 km 2 (2.70–5.41 mi 2 ). [41] Western lowland gorillas have less access to terrestrial herbs, although they can access aquatic herbs in some areas. Termites and ants are also eaten.

      Gorillas rarely drink water "because they consume succulent vegetation that is comprised of almost half water as well as morning dew", [42] although both mountain and lowland gorillas have been observed drinking.

      Social structure

      Gorillas live in groups called troops. Troops tend to be made of one adult male or silverback, multiple adult females and their offspring. [43] [44] [45] However, multiple-male troops also exist. [44] A silverback is typically more than 12 years of age, and is named for the distinctive patch of silver hair on his back, which comes with maturity. Silverbacks also have large canine teeth that also come with maturity. Both males and females tend to emigrate from their natal groups. For mountain gorillas, females disperse from their natal troops more than males. [43] [46] Mountain gorillas and western lowland gorillas also commonly transfer to second new groups. [43]

      Mature males also tend to leave their groups and establish their own troops by attracting emigrating females. However, male mountain gorillas sometimes stay in their natal troops and become subordinate to the silverback. If the silverback dies, these males may be able to become dominant or mate with the females. This behaviour has not been observed in eastern lowland gorillas. In a single male group, when the silverback dies, the females and their offspring disperse and find a new troop. [46] [47] Without a silverback to protect them, the infants will likely fall victim to infanticide. Joining a new group is likely to be a tactic against this. [46] [48] However, while gorilla troops usually disband after the silverback dies, female eastern lowlands gorillas and their offspring have been recorded staying together until a new silverback transfers into the group. This likely serves as protection from leopards. [47]

      The silverback is the centre of the troop's attention, making all the decisions, mediating conflicts, determining the movements of the group, leading the others to feeding sites, and taking responsibility for the safety and well-being of the troop. Younger males subordinate to the silverback, known as blackbacks, may serve as backup protection. Blackbacks are aged between 8 and 12 years [45] and lack the silver back hair. The bond that a silverback has with his females forms the core of gorilla social life. Bonds between them are maintained by grooming and staying close together. [49] Females form strong relationships with males to gain mating opportunities and protection from predators and infanticidal outside males. [50] However, aggressive behaviours between males and females do occur, but rarely lead to serious injury. Relationships between females may vary. Maternally related females in a troop tend to be friendly towards each other and associate closely. Otherwise, females have few friendly encounters and commonly act aggressively towards each other. [43]

      Females may fight for social access to males and a male may intervene. [49] Male gorillas have weak social bonds, particularly in multiple-male groups with apparent dominance hierarchies and strong competition for mates. Males in all-male groups, though, tend to have friendly interactions and socialise through play, grooming, and staying together, [45] and occasionally they even engage in homosexual interactions. [51] Severe aggression is rare in stable groups, but when two mountain gorilla groups meet the two silverbacks can sometimes engage in a fight to the death, using their canines to cause deep, gaping injuries. [52]

      Competition

      One possible predator of gorillas is the leopard. Gorilla remains have been found in leopard scat, but this may be the result of scavenging. [53] When the group is attacked by humans, leopards, or other gorillas, an individual silverback will protect the group, even at the cost of his own life. [54]

      Reproduction and parenting

      Females mature at 10–12 years (earlier in captivity), and males at 11–13 years. A female's first ovulatory cycle occurs when she is six years of age, and is followed by a two-year period of adolescent infertility. [55] The estrous cycle lasts 30–33 days, with outward ovulation signs subtle compared to those of chimpanzees. The gestation period lasts 8.5 months. Female mountain gorillas first give birth at 10 years of age and have four-year interbirth intervals. [55] Males can be fertile before reaching adulthood. Gorillas mate year round. [56]

      Females will purse their lips and slowly approach a male while making eye contact. This serves to urge the male to mount her. If the male does not respond, then she will try to attract his attention by reaching towards him or slapping the ground. [57] In multiple-male groups, solicitation indicates female preference, but females can be forced to mate with multiple males. [57] Males incite copulation by approaching a female and displaying at her or touching her and giving a "train grunt". [56] Recently, gorillas have been observed engaging in face-to-face sex, a trait once considered unique to humans and bonobos. [58]

      Gorilla infants are vulnerable and dependent, thus mothers, their primary caregivers, are important to their survival. [48] Male gorillas are not active in caring for the young, but they do play a role in socialising them to other youngsters. [59] The silverback has a largely supportive relationship with the infants in his troop and shields them from aggression within the group. [59] Infants remain in contact with their mothers for the first five months and mothers stay near the silverback for protection. [59] Infants suckle at least once per hour and sleep with their mothers in the same nest. [60]

      Infants begin to break contact with their mothers after five months, but only for a brief period each time. By 12 months old, infants move up to five meters (16 feet) from their mothers. At around 18–21 months, the distance between mother and offspring increases and they regularly spend time away from each other. [61] In addition, nursing decreases to once every two hours. [60] Infants spend only half of their time with their mothers by 30 months. They enter their juvenile period at their third year, and this lasts until their sixth year. At this time, gorillas are weaned and they sleep in a separate nest from their mothers. [59] After their offspring are weaned, females begin to ovulate and soon become pregnant again. [59] [60] The presence of play partners, including the silverback, minimizes conflicts in weaning between mother and offspring. [61]

      Communication

      Twenty-five distinct vocalisations are recognised, many of which are used primarily for group communication within dense vegetation. Sounds classified as grunts and barks are heard most frequently while traveling, and indicate the whereabouts of individual group members. [62] They may also be used during social interactions when discipline is required. Screams and roars signal alarm or warning, and are produced most often by silverbacks. Deep, rumbling belches suggest contentment and are heard frequently during feeding and resting periods. They are the most common form of intragroup communication. [52]

      For this reason, conflicts are most often resolved by displays and other threat behaviours that are intended to intimidate without becoming physical. As a result, they don't fight very frequently. The ritualized charge display is unique to gorillas. The entire sequence has nine steps: (1) progressively quickening hooting, (2) symbolic feeding, (3) rising bipedally, (4) throwing vegetation, (5) chest-beating with cupped hands, (6) one leg kick, (7) sideways running, two-legged to four-legged, (8) slapping and tearing vegetation, and (9) thumping the ground with palms to end display. [63]

      A gorilla's chest-beat may vary in frequency depending on its size. Smaller ones tend to have higher frequencies, while larger ones tend to be lower. They also do it the most when females are ready to mate. [64]

      Gorillas are considered highly intelligent. A few individuals in captivity, such as Koko, have been taught a subset of sign language. Like the other great apes, gorillas can laugh, grieve, have "rich emotional lives", develop strong family bonds, make and use tools, and think about the past and future. [65] Some researchers believe gorillas have spiritual feelings or religious sentiments. [1] They have been shown to have cultures in different areas revolving around different methods of food preparation, and will show individual colour preferences. [1]

      Tool use

      The following observations were made by a team led by Thomas Breuer of the Wildlife Conservation Society in September 2005. Gorillas are now known to use tools in the wild. A female gorilla in the Nouabalé-Ndoki National Park in the Republic of Congo was recorded using a stick as if to gauge the depth of water whilst crossing a swamp. A second female was seen using a tree stump as a bridge and also as a support whilst fishing in the swamp. This means all of the great apes are now known to use tools. [66]

      In September 2005, a two-and-a-half-year-old gorilla in the Republic of Congo was discovered using rocks to smash open palm nuts inside a game sanctuary. [67] While this was the first such observation for a gorilla, over 40 years previously, chimpanzees had been seen using tools in the wild 'fishing' for termites. Nonhuman great apes are endowed with semiprecision grips, and have been able to use both simple tools and even weapons, such as improvising a club from a convenient fallen branch.

      American physician and missionary Thomas Staughton Savage obtained the first specimens (the skull and other bones) during his time in Liberia. [10] The first scientific description of gorillas dates back to an article by Savage and the naturalist Jeffries Wyman in 1847 in Proceedings of the Boston Society of Natural History, [68] [69] where Troglodytes gorilla is described, now known as the western gorilla. Other species of gorilla were described in the next few years. [9]

      The explorer Paul Du Chaillu was the first westerner to see a live gorilla during his travel through western equatorial Africa from 1856 to 1859. He brought dead specimens to the UK in 1861. [70] [71] [72]

      The first systematic study was not conducted until the 1920s, when Carl Akeley of the American Museum of Natural History traveled to Africa to hunt for an animal to be shot and stuffed. On his first trip, he was accompanied by his friends Mary Bradley, a mystery writer, her husband, and their young daughter Alice, who would later write science fiction under the pseudonym James Tiptree Jr. After their trip, Mary Bradley wrote On the Gorilla Trail. She later became an advocate for the conservation of gorillas, and wrote several more books (mainly for children). In the late 1920s and early 1930s, Robert Yerkes and his wife Ava helped further the study of gorillas when they sent Harold Bigham to Africa. Yerkes also wrote a book in 1929 about the great apes.

      After World War II, George Schaller was one of the first researchers to go into the field and study primates. In 1959, he conducted a systematic study of the mountain gorilla in the wild and published his work. Years later, at the behest of Louis Leakey and the National Geographic, Dian Fossey conducted a much longer and more comprehensive study of the mountain gorilla. When she published her work, many misconceptions and myths about gorillas were finally disproved, including the myth that gorillas are violent.

      Western lowland gorillas (G. g. gorilla) are believed to be one of the zoonotic origins of HIV/AIDS. The SIVgor Simian immunodeficiency virus that infects them is similar to a certain strain of HIV-1. [73] [74] [75] [76]

      Genome sequencing

      The gorilla became the next-to-last great ape genus to have its genome sequenced. The first gorilla genome was generated with short read and Sanger sequencing using DNA from a female western lowland gorilla named Kamilah. This gave scientists further insight into the evolution and origin of humans. Despite the chimpanzees being the closest extant relatives of humans, 15% of the human genome was found to be more like that of the gorilla. [77] In addition, 30% of the gorilla genome "is closer to human or chimpanzee than the latter are to each other this is rarer around coding genes, indicating pervasive selection throughout great ape evolution, and has functional consequences in gene expression." [78] Analysis of the gorilla genome has cast doubt on the idea that the rapid evolution of hearing genes gave rise to language in humans, as it also occurred in gorillas. [79]

      Since coming to the attention of western society in the 1860s, [72] gorillas have been a recurring element of many aspects of popular culture and media. For example, gorillas have featured prominently in monstrous fantasy films such as King Kong. Additionally, pulp fiction stories such as Tarzan and Conan the Barbarian have featured gorillas as physical opponents of the titular protagonists.

      All species (and subspecies) of gorilla are listed as endangered or critically endangered on the IUCN Red List. [80] [81] Now, over 100,000 western lowland gorillas are thought to exist in the wild, with 4,000 in zoos, thanks to conservation eastern lowland gorillas have a population of under 5,000 in the wild and 24 in zoos. Mountain gorillas are the most severely endangered, with an estimated population of about 880 left in the wild and none in zoos. [1] [80] Threats to gorilla survival include habitat destruction and poaching for the bushmeat trade. Gorillas are related to humans and are susceptible to diseases that humans also get infected by, In 2004, a population of several hundred gorillas in the Odzala National Park, Republic of Congo was essentially wiped out by the Ebola virus. [82] A 2006 study published in Science concluded more than 5,000 gorillas may have died in recent outbreaks of the Ebola virus in central Africa. The researchers indicated in conjunction with commercial hunting of these apes, the virus creates "a recipe for rapid ecological extinction". [83]

      Conservation efforts include the Great Apes Survival Project, a partnership between the United Nations Environment Programme and the UNESCO, and also an international treaty, the Agreement on the Conservation of Gorillas and Their Habitats, concluded under UNEP-administered Convention on Migratory Species. The Gorilla Agreement is the first legally binding instrument exclusively targeting gorilla conservation it came into effect on 1 June 2008. Governments of countries where gorillas live placed a ban on their killing and trading, but weak law enforcement still poses a threat to them, since the governments rarely apprehend poachers, traders and consumers that rely on gorillas for profit. [84]


      Discussion

      The results of our study provide support for the ‘sexual selection’ hypothesis for sagittal cresting in gorilla and orangutan males. In G. g. gorilla and Po. pyg. pygmaeus, the timing of sagittal crest emergence in males and sex differences in temporalis muscle attachment area allometry suggest that sagittal crests do not develop solely to accommodate a large temporalis muscle, and both are consistent with the hypothesis that sexual selection contributes to sagittal cresting in males of these taxa. In contrast, in P. t. schweinfurthii and in H. lar, the frequency of sagittal cresting is low, and there is no evidence of scaling differences between the sexes, nor is there evidence in either sex that the relationship between TMAA and cranial size departs from isometry. Therefore, in these two taxa, patterns of allometric scaling provide no support for the sexual selection hypothesis. Our results show that sagittal crest size increases beyond dental maturity in G. g. gorilla and Po. pyg. pygmaeus males, and that sagittal crests in G. g. gorilla males emerge in young adults (ca. 80% of AAQ1 males possessing a sagittal crest). This contrasts with the situation in Po. pyg. pygmaeus males, where there is an abrupt increase in mid-adulthood of the percentage of male individuals possessing a sagittal crest (ca. 30% of AAQ2 males and ca. 80% of AAQ3 males possess a sagittal crest). These findings suggest that the timing of sagittal crest emergence in G. g. gorilla and Po. pyg. pygmaeus males may be a response to taxon-specific selective pressures, perhaps related to differences in their habitat and social structure, as discussed in further detail below. Our findings of positive allometry in SCS and TMAA in G. g. gorilla males, but not in females, and sex differences in scaling relationships between TMAA and cranial size, provide further support for the ‘sexual selection’ hypothesis in gorillas. The positive allometry of TMAA in Po. pyg. pygmaeus males, and the sex differences in scaling relationships between TMAA and cranial size, are also consistent with the hypothesis that sexual selection contributes to sagittal cresting in male orangutans.

      In contrast to what is found in G. g. gorilla and Po. pyg. pygmaeus, the emergence of sagittal crests in P. t. schweinfurthii and H. lar is best explained by the ‘muscle attachment’ hypothesis, based on the low frequency of sagittal cresting in males of these two taxa, the finding that scaling relationships between TMAA and cranial size do not depart from isometry in either sex, and that there are no sex differences in allometric slope. Given that our findings indicate that mastication contributes to sagittal cresting in P. t. schweinfurthii and H. lar, it is also likely that some of the variation in sagittal crest size in G. g. gorilla and Po. pyg. pygmaeus is also a result of mastication. Further research is required to investigate how much of the variation in sagittal crest size is explained by mastication and how much is explained by sexual selection.

      The finding that in the majority of G. g. gorilla males a sagittal crest develops in early adulthood, and that all males develop a sagittal crest by the second quarter of adult life, can be considered in the context of their social behaviour and male intrasexual dominance relationships. Breeding groups of G. g. gorilla are almost exclusively uni-male/multi-female (Gatti et al. 2004 Robbins et al. 2004 ). Males who reach sexual maturity early in adulthood are more likely to establish and defend a breeding group and thus enhance their reproductive success, and such a strategy is likely aided by early development of a large sagittal crest (Breuer et al. 2012 ). The timing of sagittal crest emergence in G. g. gorilla males differs from that in Po. pyg. pygmaeus, where the onset of sagittal crest development is delayed such that between the second and third adult age quartiles there is a three-fold increase in the number of male specimens exhibiting a sagittal crest. The relatively late sagittal crest development in Po. pyg. pygmaeus males coincides with a secondary growth spurt (Utami & van Hooff, 2004 ). Other evidence of a secondary growth spurt in Po. pygmaeus comes from the facial skeleton and the cranium (Röhrer-Ertl, 1988 Leutenegger & Masterson, 1989a , b Masterson & Leutenegger, 1990 , 1992 Uchida, 1996 Hens, 2003 , 2005 Balolia et al. 2013 ).

      The pattern of sagittal cresting in G. g. gorilla and Po. pyg. pygmaeus males is consistent with the nature of male intrasexual relationships in these taxa, where males of both taxa are mostly intolerant of one another and show a high intensity of intrasexual male aggression (Watts, 1996 Knott et al. 2010 ). Furthermore, there is evidence that females of these taxa prefer to mate with dominant males (Stokes et al. 2003 Knott et al. 2010 Breuer et al. 2012 ). With respect to contextualising these findings in terms of orangutan behaviour, Po. pygmaeus males employ two alternative reproductive strategies (Utami et al. 2002 ). In the first, dominant, flanged males control a territory and are intolerant of other dominant males with whom females prefer to mate (Knott et al. 2010 ). In the second, subordinate unflanged males attain reproductive success through forced copulation with females (Fox, 2002 ). Subordinate males, who can remain unflanged for up to 20 years beyond sexual maturity (Utami et al. 2002 ), use this strategy to avoid inter-male aggression from dominant males. Therefore, the late and abrupt onset of sagittal crest development in the Po. pyg. pygmaeus males examined in this study is consistent with the suggestion that sagittal crest development in Pongo males may be a secondary sexual characteristic that helps to determine dominance ranking. This explanation is consistent with interpretations by Ashton & Zuckerman ( 1956 ) who, based on the relatively late timing of sagittal crest emergence and sagittal crest development beyond dental maturity in males of some taxa, suggested that sagittal crests are ‘secondary sexual characters, induced at least partly as a result of hormonal action’ (p. 604). In this scenario, the sagittal crest may serve as a visual signal of dominance in males in that the presence of a large sagittal crest increases the height of the head in frontal and lateral profile (Caillaud et al. 2008 Breuer et al. 2012 ). Our findings of positive allometry for TMAA in G. g. gorilla and Po. pyg. pygmaeus, and for SCS in G. g. gorilla, are consistent with the proposal that if sagittal crest size varies in response to sexual selection, it will be most prominent in the males of taxa that show high levels of male intrasexual aggression. In this regard, sagittal crest size and associated musculature may be an honest indicator to females of mate quality and the ability to protect against infanticide, and of the ability to fight and to dominate other males.

      One aim of this study was to better understand the significance of sagittal crest formation in early hominin taxa, particularly in taxa that show a relatively high frequency of sagittal cresting compared with other hominins. These taxa include Par. boisei and Par. robustus (Tobias, 1967 , 1991 ), Par. aethiopicus (Walker et al. 1986 ), and Au. afarensis (Kimbel et al. 2004 ). Our results confirm previous findings that chimpanzees, one of the two great ape taxa most closely related to the early hominins, show little or no sagittal cresting, whereas some gorilla and orangutan specimens, taxa that are more distantly related to hominins, show large sagittal crests and vary in their frequency of sagittal cresting. These findings are consistent with the suggestion put forward in the introduction that strong sagittal cresting in some primate taxa evolved independently (i.e. may be a result of homoplasy) and imply that among hominin taxa, sagittal crest expression is likely to be an autapomorphic trait. What is clear is that differences in sagittal crest expression among hominids demonstrate their evolutionary plasticity, and that sagittal crest expression should be considered to have limited utility for generating phylogenetic hypotheses (cf. Lockwood & Fleagle, 1999 , p. 208), though further work is required to test this hypothesis in other parts of the primate clade. Furthermore, because the sagittal crest is a sex-specific trait, yet is not expressed in all dentally mature males and is manifest only late in ontogeny, it also has limited utility for alpha taxonomy.

      The results of the present research could alternatively be explained by sex differences in amount of food consumed, or other dietary differences between males and females. However, among Western lowland gorillas, no sex differences in diet composition have been found (Doran et al. 2002 ) and despite the large difference in overall body size, silverback mountain gorillas eat only ca. 25% more food per day than do adult females (Rothman et al. 2008 ). There is evidence of sex differences in the amount of time feeding and in diet composition among orangutans (Fox et al. 2004 Wich et al. 2006 ). Adult female orangutans spend longer periods of time feeding than do males, and this additional time is spent eating insects, rather than fruit (Fox et al. 2004 ). During periods of high fruit availability, reproductive females eat more fruit (excluding figs) and insects, and unflanged males rely more heavily on more flowers during periods of low fruit abundance (Wich et al. 2006 ). Given that these food types, with the possible exception of insects, are relatively soft, it is unlikely that sex differences in their consumption strongly impacts temporalis muscle development. There is no research of which we are aware documenting sex differences in food consumption (time spent feeding or type of food consumed) in other great ape taxa. Positive allometry has also been associated with biomechanical factors (Tseng & Rowe, 1999 Bonduriansky, 2007 ). We argue that the positive allometry for sagittal crest size in G. g. gorilla males (slope = 12.00) substantially exceeds the scaling relationships between TMAA and cranial size, so dietary or biomechanical explanations are unlikely to account for the sex differences in TMAA allometric slopes observed in G. g. gorilla and Po. pyg. pygmaeus. However, further research is required to understand the influence of diet and biomechanical factors on sex differences in sagittal cresting for taxa that show a high degree of body size dimorphism.

      A further confounding factor in understanding the relationship between the area of the neurocranium required to accommodate the temporalis muscle and sagittal crest emergence is the extent to which temporalis muscle size is associated with TMAA. There are limited data in hominoids investigating this relationship, though the data that do exist suggest that the relationship between skeletal data, measured using mandibular size measurements, and temporalis muscle physiological cross-sectional area (PCSA) is not clear-cut (Taylor & Vinyard, 2013 ). Taylor & Vinyard ( 2013 ) also show interspecific variation in temporalis fibre length among hominoid taxa, though there is no evidence to suggest a trade-off between PCSA and fibre length. Combined, these results suggest that further research into the relationship between actual temporalis muscle size, muscle architecture, and our measure of TMAA in hominoids is warranted. It is possible that sex differences in scaling relationships between TMAA and cranial size in gorillas and orangutans could be the result of differences in muscle architecture, with force potential being increased through increased pennation instead of through increased attachment area on the skull. Sex differences in temporalis muscle weight, fibre lengths and temporalis muscle PCSA, but not pennation angle, have been found in macaques (Macaca fascicularis) and these differences are suggested to be a result of sex differences in maximum gape, associated with large male canine size and associated display behaviours (Terhune et al. 2015 ). These results mean that factors other than mastication may influence sex differences in temporalis muscle architecture, which may in turn affect the amount of space on the ectocranial surface required for attachment of the temporalis muscle. Specifically, reduced pennation, or increased relative fibre length combined with larger overall muscle size, to allow for a wider gape associated with larger canines in males, would create a need for larger TMAA, and possibly drive the development of sagittal crests as a consequence of sexual selection for increased canine size. Further research investigating the association between TMAA and muscle size and architecture among hominoids, and how sex differences in maximum gape affects temporalis muscle architecture is required.

      Finally, an understanding of the biological basis of sagittal crest development related to the timing of other indicators of maturity (e.g. Shea, 1986 , 1988 Röhrer-Ertl, 1988 Leutenegger & Masterson, 1989a , b Masterson & Leutenegger, 1990 , 1992 Uchida, 1996 Hens, 2003 , 2005 Balolia et al. 2013 Gordon et al. 2013 Balolia, 2015 ), in conjunction with the need to increase muscle attachment area, have important applications for reconstructing the social behaviour of extinct primate taxa. In particular, if the timing of sagittal crest development in males is associated with a male reproductive strategy characterised by intense intrasexual competition across primates, examination of sagittal crest emergence and associated scaling relationships in fossil assemblages may allow us to begin to reconstruct the nature of intrasexual male competition in those extinct hominin taxa that display evidence of a sagittal crest. These findings raise the possibility that sagittal cresting in fossil hominin taxa such as Par. boisei may have been driven by both diet-related factors and sexual selection.

      It is important to note that hypotheses about sagittal crest emergence may be pluralistic in that sagittal crests may serve more than one function and be subject to both sexual and other aspects of natural selection (e.g. Darwin, 1871 Tomkins et al. 2010 Knell & Sampson, 2011 Padian & Horner, 2011a , b ). For example, the results of the present study indicate that sagittal crests in G. g. gorilla males provide support for both the ‘muscle attachment’ and the ‘sexual selection’ hypotheses. To further evaluate that possibility, studies investigating the relationships between temporalis muscle attachment area, muscle architecture, sagittal crest size and aspects of primate social systems in a broader range of taxa are needed. For example, evidence that sagittal crests only occur in males of robust capuchin monkeys (Lynch Alfaro et al. 2012 ) suggests that sex-specific patterns of sagittal crest emergence may not be restricted to hominoids. The finding that sagittal crest development coincides with the timing of sexual maturity and territorial displays in male California seals (Zalophus californianus), where seasonal fat deposition exaggerates the size of the sagittal crest during the reproductive season (Schusterman & Gentry, 1971 ), provides further evidence that sagittal crests may emerge in response to sexual selection in a diverse range of mammalian taxa.

      Although sagittal crest expression can be considered to have limited utility for generating phylogenetic hypotheses, our results indicate that patterns of sagittal crest development may provide some insight into sociality in the extinct hominin taxa in which they do occur. For example, further investigations could test the hypothesis that the sagittal crest in the males of some extant taxa emerges around the time individuals begin to exercise social dominance, and thus provide support for Ashton & Zuckerman's ( 1956 ) hypothesis that the sagittal crest in males is a secondary sexual characteristic, subject to sexual selection. Similar suggestions have been made with respect to the emergence of silverback hair in fully mature gorillas, and facial flanges and a developed throat sac in mature male orangutans (Watts, 1991 Utami et al. 2002 ). But while it makes sense to investigate whether sagittal crest emergence coincides with the time at which males of some taxa attain dominance status, it is also necessary to evaluate the potential for sexual selection of crest expression against the background requirement of increasing muscle attachment area with increasing body size (Robinson, 1958 ). It is possible that in Par. boisei, which has unusually small and sexually monomorphic canines (Wood & Constantino, 2007 ), the sagittal crest may have replaced canine size as a signalling mechanism.

      In conclusion, the scaling patterns reported here, and the timing of sagittal crest emergence in gorilla and orangutan males provide support for the hypothesis that sexual selection contributes to the formation of sagittal crests in some hominoid primates. To what extent sagittal crests may serve a direct function in social signalling, and to what extent they are a consequence of biomechanical constraints imposed on males to accommodate wider gapes and, hence, a correlate of canine size, remains unresolved without further data on temporalis muscle architecture, and on fitness consequences and behavioural correlates of sagittal crest size in hominoids.


      Contents

      The word "gorilla" comes from the history of Hanno the Navigator (c. 500 BC), a Carthaginian explorer on an expedition to the west African coast to the area that later became Sierra Leone. [5] [6] Members of the expedition encountered "savage people, the greater part of whom were women, whose bodies were hairy, and whom our interpreters called Gorillae". [7] [8] It is unknown whether what the explorers encountered were what we now call gorillas, another species of ape or monkeys, or humans. [9] Skins of gorillai women, brought back by Hanno, are reputed to have been kept at Carthage until Rome destroyed the city 350 years later at the end of the Punic Wars, 146 BC.

      The American physician and missionary Thomas Staughton Savage and naturalist Jeffries Wyman first described the western gorilla (they called it Troglodytes gorilla) in 1847 from specimens obtained in Liberia. [10] The name was derived from Ancient Greek Γόριλλαι (gorillai) 'tribe of hairy women', [11] described by Hanno.

      The closest relatives of gorillas are the other two Homininae genera, chimpanzees and humans, all of them having diverged from a common ancestor about 7 million years ago. [12] Human gene sequences differ only 1.6% on average from the sequences of corresponding gorilla genes, but there is further difference in how many copies each gene has. [13] Until recently, gorillas were considered to be a single species, with three subspecies: the western lowland gorilla, the eastern lowland gorilla and the mountain gorilla. [9] [14] There is now agreement that there are two species, each with two subspecies. More recently, a third subspecies has been claimed to exist in one of the species. The separate species and subspecies developed from a single type of gorilla during the Ice Age, when their forest habitats shrank and became isolated from each other. [1]

      Primatologists continue to explore the relationships between various gorilla populations. [9] The species and subspecies listed here are the ones upon which most scientists agree. [15]

        Genus Gorilla
          (G. gorilla)
            (G. g. gorilla) (G. g. diehli)
            (G. b. beringei) (G. b. graueri)

          chimpanzees (genus Pan)

          gorillas (genus Gorilla)

          orangutans (genus Pongo)

          gibbons (family Hylobatidae)

          The proposed third subspecies of Gorilla beringei, which has not yet received a trinomen, is the Bwindi population of the mountain gorilla, sometimes called the Bwindi gorilla.

          Some variations that distinguish the classifications of gorilla include varying density, size, hair colour, length, culture, and facial widths. [1] Population genetics of the lowland gorillas suggest that the western and eastern lowland populations diverged

          Gorillas move around by knuckle-walking, although they sometimes walk upright for short distances, typically while carrying food or in defensive situations. [19] A 2018 study investigating the hand posture of 77 mountain gorillas at Bwindi Impenetrable National Park (8% of the population) found that knuckle walking was done only 60% of the time, and they also supported their weight on their fists, the backs of their hands/feet, and on their palms/soles (with the digits flexed). Such a range of hand postures was previously thought to have been used by only orangutans. [20] Studies of gorilla handedness have yielded varying results, with some arguing for no preference for either hand, and others right-hand dominance for the general population. [21]

          Wild male gorillas weigh 136 to 227 kg (300 to 500 lb), while adult females weigh 68–113 kg (150–250 lb). [22] [23] Adult males are 1.4 to 1.8 m (4 ft 7 in to 5 ft 11 in) tall, with an arm span that stretches from 2.3 to 2.6 m (7 ft 7 in to 8 ft 6 in). Female gorillas are shorter at 1.25 to 1.5 m (4 ft 1 in to 4 ft 11 in), with smaller arm spans. [24] [25] [26] [27] Groves (1970) calculated the average weight of 42 wild adult male gorillas at 144 kg, while Smith and Jungers (1997) found the average weight of 19 wild adult male gorillas to be 169 kg. [28] [29] Adult male gorillas are known as silverbacks due to the characteristic silver hair on their backs reaching to the hips. The tallest gorilla recorded was a 1.95 m (6 ft 5 in) silverback with an arm span of 2.7 m (8 ft 10 in), a chest of 1.98 m (6 ft 6 in), and a weight of 219 kg (483 lb), shot in Alimbongo, northern Kivu in May 1938. [27] The heaviest gorilla recorded was a 1.83 m (6 ft 0 in) silverback shot in Ambam, Cameroon, which weighed 267 kg (589 lb). [27] Males in captivity can be overweight and reach weights up to 310 kg (683 lb). [27]

          The eastern gorilla is more darkly coloured than the western gorilla, with the mountain gorilla being the darkest of all. The mountain gorilla also has the thickest hair. The western lowland gorilla can be brown or greyish with a reddish forehead. In addition, gorillas that live in lowland forest are more slender and agile than the more bulky mountain gorillas. The eastern gorilla also has a longer face and broader chest than the western gorilla. [30] Like humans, gorillas have individual fingerprints. [31] [32] Their eye colour is dark brown, framed by a black ring around the iris. Gorilla facial structure is described as mandibular prognathism, that is, the mandible protrudes farther out than the maxilla. Adult males also have a prominent sagittal crest.

          Studies have shown gorilla blood is not reactive to anti-A and anti-B monoclonal antibodies, which would, in humans, indicate type O blood. Due to novel sequences, though, it is different enough to not conform with the human ABO blood group system, into which the other great apes fit. [33]

          A gorilla's lifespan is normally between 35 and 40 years, although zoo gorillas may live for 50 years or more. Colo, a female western gorilla at the Columbus Zoo and Aquarium, was the oldest known gorilla at 60 years of age when she died on 17 January 2017. [34]

          Gorillas have a patchy distribution. The range of the two species is separated by the Congo River and its tributaries. The western gorilla lives in west central Africa, while the eastern gorilla lives in east central Africa. Between the species, and even within the species, gorillas live in a variety of habitats and elevations. Gorilla habitat ranges from montane forest to swampland. Eastern gorillas inhabit montane and submontane forest between 650 and 4,000 m (2,130 and 13,120 ft) above sea level. [35] Mountain gorillas live in montane forest at the higher end of the elevation range, while eastern lowland gorillas live in submontane forest at the lower end. In addition, eastern lowland gorillas live in montane bamboo forest, as well as lowland forest ranging from 600–3,308 m (1,969–10,853 ft) in elevation. [36] Western gorillas live in both lowland swamp forest and montane forest, at elevations ranging from sea level to 1,600 m (5,200 ft). [35] Western lowland gorillas live in swamp and lowland forest ranging up to 1,600 m (5,200 ft), and Cross River gorillas live in low-lying and submontane forest ranging from 150–1,600 m (490–5,250 ft).

          Nesting

          Gorillas construct nests for daytime and night use. Nests tend to be simple aggregations of branches and leaves about 2 to 5 ft (0.61 to 1.52 m) in diameter and are constructed by individuals. Gorillas, unlike chimpanzees or orangutans, tend to sleep in nests on the ground. The young nest with their mothers, but construct nests after three years of age, initially close to those of their mothers. [37] Gorilla nests are distributed arbitrarily and use of tree species for site and construction appears to be opportunistic. [38] Nest-building by great apes is now considered to be not just animal architecture, but as an important instance of tool use. [38]

          A gorilla's day is divided between rest periods and travel or feeding periods. Diets differ between and within species. Mountain gorillas mostly eat foliage, such as leaves, stems, pith, and shoots, while fruit makes up a very small part of their diets. [39] Mountain gorilla food is widely distributed and neither individuals nor groups have to compete with one another. Their home ranges vary from 3 to 15 km 2 (1.16 to 5.79 mi 2 ), and their movements range around 500 m (0.31 mi) or less on an average day. [39] Despite eating a few species in each habitat, mountain gorillas have flexible diets and can live in a variety of habitats. [39]

          Eastern lowland gorillas have more diverse diets, which vary seasonally. Leaves and pith are commonly eaten, but fruits can make up as much as 25% of their diets. Since fruit is less available, lowland gorillas must travel farther each day, and their home ranges vary from 2.7 to 6.5 km 2 (1.04 to 2.51 mi 2 ), with day ranges 154–2,280 m (0.096–1.417 mi). Eastern lowland gorillas will also eat insects, preferably ants. [40] Western lowland gorillas depend on fruits more than the others and they are more dispersed across their range. [41] They travel even farther than the other gorilla subspecies, at 1,105 m (0.687 mi) per day on average, and have larger home ranges of 7–14 km 2 (2.70–5.41 mi 2 ). [41] Western lowland gorillas have less access to terrestrial herbs, although they can access aquatic herbs in some areas. Termites and ants are also eaten.

          Gorillas rarely drink water "because they consume succulent vegetation that is comprised of almost half water as well as morning dew", [42] although both mountain and lowland gorillas have been observed drinking.

          Social structure

          Gorillas live in groups called troops. Troops tend to be made of one adult male or silverback, multiple adult females and their offspring. [43] [44] [45] However, multiple-male troops also exist. [44] A silverback is typically more than 12 years of age, and is named for the distinctive patch of silver hair on his back, which comes with maturity. Silverbacks also have large canine teeth that also come with maturity. Both males and females tend to emigrate from their natal groups. For mountain gorillas, females disperse from their natal troops more than males. [43] [46] Mountain gorillas and western lowland gorillas also commonly transfer to second new groups. [43]

          Mature males also tend to leave their groups and establish their own troops by attracting emigrating females. However, male mountain gorillas sometimes stay in their natal troops and become subordinate to the silverback. If the silverback dies, these males may be able to become dominant or mate with the females. This behaviour has not been observed in eastern lowland gorillas. In a single male group, when the silverback dies, the females and their offspring disperse and find a new troop. [46] [47] Without a silverback to protect them, the infants will likely fall victim to infanticide. Joining a new group is likely to be a tactic against this. [46] [48] However, while gorilla troops usually disband after the silverback dies, female eastern lowlands gorillas and their offspring have been recorded staying together until a new silverback transfers into the group. This likely serves as protection from leopards. [47]

          The silverback is the centre of the troop's attention, making all the decisions, mediating conflicts, determining the movements of the group, leading the others to feeding sites, and taking responsibility for the safety and well-being of the troop. Younger males subordinate to the silverback, known as blackbacks, may serve as backup protection. Blackbacks are aged between 8 and 12 years [45] and lack the silver back hair. The bond that a silverback has with his females forms the core of gorilla social life. Bonds between them are maintained by grooming and staying close together. [49] Females form strong relationships with males to gain mating opportunities and protection from predators and infanticidal outside males. [50] However, aggressive behaviours between males and females do occur, but rarely lead to serious injury. Relationships between females may vary. Maternally related females in a troop tend to be friendly towards each other and associate closely. Otherwise, females have few friendly encounters and commonly act aggressively towards each other. [43]

          Females may fight for social access to males and a male may intervene. [49] Male gorillas have weak social bonds, particularly in multiple-male groups with apparent dominance hierarchies and strong competition for mates. Males in all-male groups, though, tend to have friendly interactions and socialise through play, grooming, and staying together, [45] and occasionally they even engage in homosexual interactions. [51] Severe aggression is rare in stable groups, but when two mountain gorilla groups meet the two silverbacks can sometimes engage in a fight to the death, using their canines to cause deep, gaping injuries. [52]

          Competition

          One possible predator of gorillas is the leopard. Gorilla remains have been found in leopard scat, but this may be the result of scavenging. [53] When the group is attacked by humans, leopards, or other gorillas, an individual silverback will protect the group, even at the cost of his own life. [54]

          Reproduction and parenting

          Females mature at 10–12 years (earlier in captivity), and males at 11–13 years. A female's first ovulatory cycle occurs when she is six years of age, and is followed by a two-year period of adolescent infertility. [55] The estrous cycle lasts 30–33 days, with outward ovulation signs subtle compared to those of chimpanzees. The gestation period lasts 8.5 months. Female mountain gorillas first give birth at 10 years of age and have four-year interbirth intervals. [55] Males can be fertile before reaching adulthood. Gorillas mate year round. [56]

          Females will purse their lips and slowly approach a male while making eye contact. This serves to urge the male to mount her. If the male does not respond, then she will try to attract his attention by reaching towards him or slapping the ground. [57] In multiple-male groups, solicitation indicates female preference, but females can be forced to mate with multiple males. [57] Males incite copulation by approaching a female and displaying at her or touching her and giving a "train grunt". [56] Recently, gorillas have been observed engaging in face-to-face sex, a trait once considered unique to humans and bonobos. [58]

          Gorilla infants are vulnerable and dependent, thus mothers, their primary caregivers, are important to their survival. [48] Male gorillas are not active in caring for the young, but they do play a role in socialising them to other youngsters. [59] The silverback has a largely supportive relationship with the infants in his troop and shields them from aggression within the group. [59] Infants remain in contact with their mothers for the first five months and mothers stay near the silverback for protection. [59] Infants suckle at least once per hour and sleep with their mothers in the same nest. [60]

          Infants begin to break contact with their mothers after five months, but only for a brief period each time. By 12 months old, infants move up to five meters (16 feet) from their mothers. At around 18–21 months, the distance between mother and offspring increases and they regularly spend time away from each other. [61] In addition, nursing decreases to once every two hours. [60] Infants spend only half of their time with their mothers by 30 months. They enter their juvenile period at their third year, and this lasts until their sixth year. At this time, gorillas are weaned and they sleep in a separate nest from their mothers. [59] After their offspring are weaned, females begin to ovulate and soon become pregnant again. [59] [60] The presence of play partners, including the silverback, minimizes conflicts in weaning between mother and offspring. [61]

          Communication

          Twenty-five distinct vocalisations are recognised, many of which are used primarily for group communication within dense vegetation. Sounds classified as grunts and barks are heard most frequently while traveling, and indicate the whereabouts of individual group members. [62] They may also be used during social interactions when discipline is required. Screams and roars signal alarm or warning, and are produced most often by silverbacks. Deep, rumbling belches suggest contentment and are heard frequently during feeding and resting periods. They are the most common form of intragroup communication. [52]

          For this reason, conflicts are most often resolved by displays and other threat behaviours that are intended to intimidate without becoming physical. As a result, they don't fight very frequently. The ritualized charge display is unique to gorillas. The entire sequence has nine steps: (1) progressively quickening hooting, (2) symbolic feeding, (3) rising bipedally, (4) throwing vegetation, (5) chest-beating with cupped hands, (6) one leg kick, (7) sideways running, two-legged to four-legged, (8) slapping and tearing vegetation, and (9) thumping the ground with palms to end display. [63]

          A gorilla's chest-beat may vary in frequency depending on its size. Smaller ones tend to have higher frequencies, while larger ones tend to be lower. They also do it the most when females are ready to mate. [64]

          Gorillas are considered highly intelligent. A few individuals in captivity, such as Koko, have been taught a subset of sign language. Like the other great apes, gorillas can laugh, grieve, have "rich emotional lives", develop strong family bonds, make and use tools, and think about the past and future. [65] Some researchers believe gorillas have spiritual feelings or religious sentiments. [1] They have been shown to have cultures in different areas revolving around different methods of food preparation, and will show individual colour preferences. [1]

          Tool use

          The following observations were made by a team led by Thomas Breuer of the Wildlife Conservation Society in September 2005. Gorillas are now known to use tools in the wild. A female gorilla in the Nouabalé-Ndoki National Park in the Republic of Congo was recorded using a stick as if to gauge the depth of water whilst crossing a swamp. A second female was seen using a tree stump as a bridge and also as a support whilst fishing in the swamp. This means all of the great apes are now known to use tools. [66]

          In September 2005, a two-and-a-half-year-old gorilla in the Republic of Congo was discovered using rocks to smash open palm nuts inside a game sanctuary. [67] While this was the first such observation for a gorilla, over 40 years previously, chimpanzees had been seen using tools in the wild 'fishing' for termites. Nonhuman great apes are endowed with semiprecision grips, and have been able to use both simple tools and even weapons, such as improvising a club from a convenient fallen branch.

          American physician and missionary Thomas Staughton Savage obtained the first specimens (the skull and other bones) during his time in Liberia. [10] The first scientific description of gorillas dates back to an article by Savage and the naturalist Jeffries Wyman in 1847 in Proceedings of the Boston Society of Natural History, [68] [69] where Troglodytes gorilla is described, now known as the western gorilla. Other species of gorilla were described in the next few years. [9]

          The explorer Paul Du Chaillu was the first westerner to see a live gorilla during his travel through western equatorial Africa from 1856 to 1859. He brought dead specimens to the UK in 1861. [70] [71] [72]

          The first systematic study was not conducted until the 1920s, when Carl Akeley of the American Museum of Natural History traveled to Africa to hunt for an animal to be shot and stuffed. On his first trip, he was accompanied by his friends Mary Bradley, a mystery writer, her husband, and their young daughter Alice, who would later write science fiction under the pseudonym James Tiptree Jr. After their trip, Mary Bradley wrote On the Gorilla Trail. She later became an advocate for the conservation of gorillas, and wrote several more books (mainly for children). In the late 1920s and early 1930s, Robert Yerkes and his wife Ava helped further the study of gorillas when they sent Harold Bigham to Africa. Yerkes also wrote a book in 1929 about the great apes.

          After World War II, George Schaller was one of the first researchers to go into the field and study primates. In 1959, he conducted a systematic study of the mountain gorilla in the wild and published his work. Years later, at the behest of Louis Leakey and the National Geographic, Dian Fossey conducted a much longer and more comprehensive study of the mountain gorilla. When she published her work, many misconceptions and myths about gorillas were finally disproved, including the myth that gorillas are violent.

          Western lowland gorillas (G. g. gorilla) are believed to be one of the zoonotic origins of HIV/AIDS. The SIVgor Simian immunodeficiency virus that infects them is similar to a certain strain of HIV-1. [73] [74] [75] [76]

          Genome sequencing

          The gorilla became the next-to-last great ape genus to have its genome sequenced. The first gorilla genome was generated with short read and Sanger sequencing using DNA from a female western lowland gorilla named Kamilah. This gave scientists further insight into the evolution and origin of humans. Despite the chimpanzees being the closest extant relatives of humans, 15% of the human genome was found to be more like that of the gorilla. [77] In addition, 30% of the gorilla genome "is closer to human or chimpanzee than the latter are to each other this is rarer around coding genes, indicating pervasive selection throughout great ape evolution, and has functional consequences in gene expression." [78] Analysis of the gorilla genome has cast doubt on the idea that the rapid evolution of hearing genes gave rise to language in humans, as it also occurred in gorillas. [79]

          Since coming to the attention of western society in the 1860s, [72] gorillas have been a recurring element of many aspects of popular culture and media. For example, gorillas have featured prominently in monstrous fantasy films such as King Kong. Additionally, pulp fiction stories such as Tarzan and Conan the Barbarian have featured gorillas as physical opponents of the titular protagonists.

          All species (and subspecies) of gorilla are listed as endangered or critically endangered on the IUCN Red List. [80] [81] Now, over 100,000 western lowland gorillas are thought to exist in the wild, with 4,000 in zoos, thanks to conservation eastern lowland gorillas have a population of under 5,000 in the wild and 24 in zoos. Mountain gorillas are the most severely endangered, with an estimated population of about 880 left in the wild and none in zoos. [1] [80] Threats to gorilla survival include habitat destruction and poaching for the bushmeat trade. Gorillas are related to humans and are susceptible to diseases that humans also get infected by, In 2004, a population of several hundred gorillas in the Odzala National Park, Republic of Congo was essentially wiped out by the Ebola virus. [82] A 2006 study published in Science concluded more than 5,000 gorillas may have died in recent outbreaks of the Ebola virus in central Africa. The researchers indicated in conjunction with commercial hunting of these apes, the virus creates "a recipe for rapid ecological extinction". [83]

          Conservation efforts include the Great Apes Survival Project, a partnership between the United Nations Environment Programme and the UNESCO, and also an international treaty, the Agreement on the Conservation of Gorillas and Their Habitats, concluded under UNEP-administered Convention on Migratory Species. The Gorilla Agreement is the first legally binding instrument exclusively targeting gorilla conservation it came into effect on 1 June 2008. Governments of countries where gorillas live placed a ban on their killing and trading, but weak law enforcement still poses a threat to them, since the governments rarely apprehend poachers, traders and consumers that rely on gorillas for profit. [84]


          Conservation

          Population size and growth rates

          Conservation efforts have led to an apparent increase in overall population of the mountain gorilla (Gorilla beringei beringei) in the Virungas and at Bwindi. The overall population is now believed to be approximately 790 individuals, [ 30 ] with 4 of them being in care of the Senkwekwe Centre orphanage in the DR of Congo.

          In December 2010 the official website of Virunga National Park announced that "the number of mountain gorillas living in the tri-national forested area of which Virunga forms a part, has increased by 26.3% over the last seven years - an average growth rate of 3.7% per annum." [ 30 ] The 2010 census estimated that 480 mountain gorillas inhabited the region. The 2003 census had estimated the Virunga gorilla population to be 380 individuals which represented a 17 % increase in the total population since 1989 when there were 320 individuals [ 31 ] The population has almost doubled since its nadir in 1981, when a census estimated that only 254 gorillas remained. [ 32 ]

          The 2006 census at Bwindi indicated a population of 340 gorillas, representing a 6% increase in total population size since 2002 and a 12% increase from 320 individuals in 1997. [ 33 ] All of those estimates were based on traditional census methods using dung samples collected at night nests. Conversely, genetic analyses of the entire population during the 2006 census indicated there were only approximately 300 individuals in Bwindi. [ 2 ] The discrepancy highlights the difficulty in using imprecise census data to estimate population growth.

          In both Bwindi and the Virungas, groups of gorillas that were habituated for research and ecotourism have higher growth rates than unhabituated gorillas, according to computer modeling of their population dynamics. [ 29 ] [ 34 ] Habituation means that through repeated, neutral contact with humans, gorillas exhibit normal behavior when people are in close proximity. Habituated gorillas are more closely guarded by field staff and they receive veterinary treatment for snares, respiratory disease, and other life-threatening conditions. [ 34 ] Nonetheless, researchers recommended that some gorillas remain unhabituated as a bet-hedging strategy against the risk of human pathogens being transmitted throughout the population. [ 34 ]

          Despite their recent population growth, the mountain gorilla remains threatened. Mountain gorillas (Gorilla beringei beringei) are listed as Endangered on the IUCN Red List. Endangered means the maximum population reduction over a three-generation (i.e. 60-year) period from the 1970s to 2030 is suspected to exceed 50%, hence qualifying this species for Endangered under criterion A4. [ 2 ]

          Threats

          As with any flora and fauna, the decline of a population can usually be attributed to anthropogenic factors. [ 35 ] Pollution, habitat destruction and fragmentation, over harvesting (in the form of illegal poaching), agriculture, and the introduction of diseases are some of the usual suspects the mountain gorilla suffers from all of these. All of the aforementioned are due to the most significant threat to gorilla survival human population growth [ 36 ]

          Poaching: Mountain gorillas are not usually hunted for bushmeat, but they are frequently maimed or killed by traps and snares intended for other animals. They have been killed for their heads, hands, and feet, which are sold to collectors. Infants are sold to zoos, researchers, and people who want them as pets. The abduction of infants generally involves the loss of at least one adult, as members of a group will fight to the death to protect their young. The Virunga gorillas are particularly susceptible to animal trafficking for the illegal pet trade. With young gorillas worth from $1000 to $5000 on the black market, poachers seeking infant and juvenile specimens will kill and wound other members of the group in the process. [ 37 ] Those of the group that survive often disband. One well documented case was that known as the ‘Taiping 4’. In this situation, a Malaysian Zoo received four wild-born infant gorillas from Nigeria at a cost of US$1.6 million using falsified export documents. [ 38 ] [ 39 ] Poaching for meat is also particularly threatening in regions of political unrest. Most of the African great apes survive in areas of chronic insecurity, where there is a breakdown of law and order. The killing of mountain gorillas at Bikenge in Virunga National Park in January 2007 was a well documented case.

          Habitat loss: This is one the most severe threats to gorilla populations. The forests where mountain gorillas live are surrounded by rapidly increasing human settlement. Through shifting (slash-and-burn) agriculture, pastoral expansion and logging, villages in forest zones cause fragmentation and degradation of habitat. [ 40 ] The late 1960s saw the Virunga Conservation Area (VCA) of Rwanda’s national park reduced by more than half of its original size to support the cultivation of Pyrethrum. This led to a massive reduction in mountain gorilla population numbers by the mid-1970s. [ 41 ] The resulting deforestation confines the gorillas to isolated deserts. Some groups may raid crops for food, creating further animosity and retaliation. The impact of habitat loss extends beyond the reduction of suitable living space for gorillas. As gorilla groups are increasingly geographically isolated from one another due to human settlements, the genetic diversity of each group is reduced. Some signs of inbreeding are already appearing in younger gorillas, including webbed hands and feet. [ 42 ]

          Disease: Despite the protection garnered from being located in National parks, the mountain gorilla is also at risk from people of a more well-meaning nature. Groups subjected to regular visits from tourists and locals are at a continued risk of disease cross-transmission (Lilly et al., 2002) - this is in spite of attempts to enforce a rule that humans and gorillas be separated by a distance of 7 metres at all times to prevent this. [ 34 ] With a similar genetic makeup to humans and an immune system that has not evolved to cope with human disease, this poses a serious conservation threat. [ 43 ] Indeed, according to some researchers, infectious diseases (predominantly respiratory) are responsible for about 20% of sudden deaths in mountain gorilla populations. [ 44 ] It is notable that with the implementation of a successful ecotourism program in which human-gorilla interaction was minimised, during the period of 1989-2000 four sub-populations in Rwanda experienced an increase of 76%. By contrast, seven of the commonly visited sub-populations in the Democratic Republic of Congo (DRC) saw a decline of almost 20% over only four years (1996–2000). [ 45 ] From this, we [ who? ] can conclude that the negative impacts of ecotourism on gorilla health can be minimised if proper management is undertaken.

          The risk of disease transmission is not limited to those of a human origin pathogens from domestic animals and livestock through contaminated water are also a concern. [ 46 ] Studies have found that water borne, gastrointestinal parasites such as Cryptosporidium sp., Microsporidia sp.,and Giardia sp. are genetically identical when found in livestock, humans, and gorillas particularly along theborder of the Bwindi Impenetrable Forest, Uganda. [ 47 ] [ 48 ] Another example of human induced disease is Tuberculosis Kabagambe et al. [ 37 ] found that as high as 11% of cattle in Rwanda suffered from this affliction.

          War and civil unrest: Rwanda, Uganda and the Democratic Republic of Congo have been politically unstable and beleaguered by war and civil unrest over the last decades. Simulation modeling, Byers et al. (2003) has suggested that times of war and unrest have negative impacts on the habitat and populations of mountain gorillas. [ 49 ] For example, events such as 1994’s Rwanda genocide would take place approximately every 30 years, with each event lasting for 10 years. Due to the increase in human encounters, aggressive and passive alike, this would result in a rise in mortality rates and a decrease in reproductive success. [ 40 ] More direct impacts from conflict can also be seen. Kanyamibwa notes that there were reports that mines were placed along trails in the Volcanos National Park, and that many gorillas were killed as a result. [ 50 ] Pressure from habitat destruction in the form of logging also increased as refugees fled the cities and cut down trees for wood. [ 50 ] During the Rwandan genocide, some poaching activity was also linked to the general breakdown of law and order and lack of any ramifications. [ 51 ]

          Conservation efforts

          The main International Non-Government Organization involved in conservation of mountain gorillas is the International Gorilla Conservation Programme, which was established in 1991 as a joint effort of the African Wildlife Foundation, Fauna & Flora International and the World Wide Fund for Nature. [ 52 ] Conservation requires work at many levels, from local to international, and involves protection and law enforcement as well as research and education. Dian Fossey broke down conservation efforts into the following three categories:

          Active conservation includes frequent patrols in wildlife areas to destroy poacher equipment and weapons, firm and prompt law enforcement, census counts in regions of breeding and ranging concentration, and strong safeguards for the limited habitat the animals occupy."

          Theoretical conservation seeks to encourage growth in tourism by improving existing roads that circle the mountains, by renovating the park headquarters and tourists' lodging, and by the habituation of gorillas near the park boundaries for tourists to visit and photograph."

          Community-based conservation management involves biodiversity protection by, for, and with the local community [ 53 ] in practise this is applied in varying degrees. The process seeks equity between meeting the needs of the local population and preserving the protected areas and involves local people in decision making processes.

          A collaborative management process has had some success in the Bwindi National Park. The forest was gazetted to National Park in 1991 this occurred with little community consultation and the new status prohibited local people from accessing resources within the park as well as reduced economic opportunities. Subsequently a number of forest fires were deliberately lit and threats were made to the gorillas. [ 54 ] To counteract this, three schemes to provide benefits from existence of the forest communities and involve the local community in park management were developed. They included agreements allowing the controlled harvesting of resources in the park, receipt of some revenue from tourism and establishment of a trust fund partly for community development. Tension between people and park have been reduced [ 54 ] and now there is more willingness to take part in gorilla protection. [ 55 ] Surveys of community attitudes conducted by CARE show a steadily increasing proportion of the people in favour of the park. More than that there have been no cases of deliberate burning and the problem of snares in these areas has been reduced. [ 55 ] The introduction of ceremonies such as Kwita Izina (in 2005) has also had some impact in drawing attention to gorilla preservation and its importance to local communities.

          While community-based conservation bears out individual analysis, there are significant overlaps between active and theoretical conservation and a discussion of the two as halves of a whole seems more constructive. For example, in 2002 Rwanda's national parks went through a restructuring process. The director of the IGCP, Eugene Rutagarama stated that “They got more rangers on better salaries, more radios, more patrol cars and better training in wildlife conservation. They also built more shelters in the park, from which rangers could protect the gorillas". [ 56 ] The funding for these types of improvements usually comes from tourism - in 2008, approximately 20 000 tourists visited gorilla populations in Rwanda, generating around $8 million in revenue for the parks. [ 34 ] In Uganda too, tourism is seen as a “high value activity that generates enough revenue to cover park management costs and contribute to the national budget of the Uganda Wildlife Authority." [ 57 ] Furthermore, tourist visits which are conducted by park rangers also allow censuses of gorilla sub-populations to be undertaken concurrently. [ 29 ]

          In addition to tourism, other measures for conservation of the sub-population can be taken such as ensuring connecting corridors between isolated areas to make movement between them easier and safer. [ 58 ]


          Earliest known Hominins

          Molecular genetics tells us that humans, gorillas, bonobos and chimpanzees are all descended from a common ancestor that lived sometime between 7.5 million and 6.5 million years ago. All of the earliest known hominin fossils have been found in Central and Eastern Africa (Figure 4.25).

          Sahelanthropus tchadensis lived sometime between 7.0 and 6.0 million years ago in Chad in West-Central Africa, making it the oldest known hominin to date. The species is represented by a mostly complete but distorted cranium and additional cranial fragments. Walking upright may have helped this species survive in diverse habitats, including forests and grasslands. Although there are no postcranial remains of

          Figure 4.24: Timeline and evolutionary relationships of major hominin species

          Figure 4.25: Sites of significant early hominin and australopithecine fossil discoveries

          Sahelanthropus, we do know this species had a combination of ape-like and human-like features. Ape-like features included a brain slightly smaller than a chimpanzee’s, a sloping face, very prominent brow ridges, and elongated skull form. Human-like features included small canine teeth, a short mid-facial region, and the shape and central positioning of the foramen magnum under the skull suggest the ability to walk upright. Unfortunately, most of Sahelanthropus’ teeth are heavily worn however, based on its environment and other early human species, it probably ate a mainly plant-based diet. This likely included leaves, fruit, seeds, roots, nuts, and insects.

          Also living around 6.0 million years ago, Orrorin tugenensis is among the oldest early hominins. At least five individuals of this species were found near Lake Turkana in the Tugen Hills of Kenya, in Eastern Africa. Fossil remains of this species include bones of the arms and legs, parts of fingers and several teeth. Individuals of this species were approximately the size of a chimpanzee, standing less than 1 m (3.3 ft) tall, and had small teeth with thick enamel, similar to modern humans. From Orrorin ‘s low, rounded molars and small canine teeth, paleoanthropologists can infer that this species ate mainly a plant-based diet. The bones of the hand were curved like a living ape’s, suggesting that this species spent time in the trees however, the most important fossil of this species is the upper portion of a femur, with the angled part more closely resembling that of a human. It formed a strong bridge with the hip to support the body’s weight, showing evidence typical of a biped – meaning Orrorin tugenensis individuals climbed trees but also probably walked bipedally.

          Ardipithecus kadabba lived sometime between 5.8 and 5.5 million years ago in the Middle Awash Valley of Ethiopia in Eastern Africa. The species is represented by several teeth, partial arms, a clavicle, and hand and foot bones. Evidence for Ar. kadabba ’s bipedalism comes from a single toe bone that has a broad, robust appearance, suggesting its use in bipedal walking however, the hand bones retain an ape-like curvature suggestive of time spent in trees. These individuals were probably similar in body and brain size to a modern chimpanzee and had larger canines. Instead of eating mostly fruit and soft leaves like chimpanzees, there is evidence that Ar. kadabba ate a variety of foods. The back teeth of Ar. kadabba are larger than a chimpanzee’s, but its front teeth are narrower suggesting this species did most of its chewing in the back of its mouth with a focus on hard-to-eat foods like fibrous nuts.

          Over 100 specimens of Ardipithecus ramidus fossil remains have been discovered in Middle Awash Valley and Gona, Ethiopia in Eastern Africa. This species had an elongated skull, a sloping face, very prominent brow ridges, and small brain, slightly smaller than a chimpanzee’s and roughly 20% the size of the modern Homo sapiens brain. A good sample of canine teeth of this species indicates very little difference in size between males and females in this species. Ar. ramidus individuals were most likely omnivores, which means they enjoyed more generalized diet of plants, meat, and fruit, and did not seem to eat hard, abrasive foods like nuts and tubers, which is consistent with the dentition having thinner enamel than what is seen in earlier hominin species.

          Date(s): 7.0-6.0 million years ago

          Habitat: Flooded grasslands, open woodlands

          • Ape-like elongated skull with massive, heavy brow ridge and sloping face foramen magnum located at bottom of skull
          • Very small brain (

          Date(s): 6.2-5.6 million years ago

          Habitat: Forest and wet woodlands

          • Shape of femur indicates probable bipedalism
          • Ape-like curved bones in hands
          • Similar is size to modern chimpanzee
          • Small teeth with thick enamel

          Date(s): 5.8-5.5 million years ago

          Habitat: Woodlands, grasslands and open lake areas

          • Femur and pelvis indicate probable bipedalism
          • Similar is size to modern chimpanzee
          • Ape-like curved bones in feet
          • Larger back teeth and canines with thick enamel

          Date(s): 4.5-4.3 million years ago

          Habitat: Woodlands, grasslands and open lake areas

          • Elongated skull with heavy brow ridge, sloping face
          • Very small brain (

          The ‘Ardi’ skeleton is the most complete early hominin specimen and reflects a particular mosaic of ape- and human-like characteristics not seen in later hominins. Ardi weighed about 50 kg (110 lb) and was up to 1.2 m (3.9 ft) tall. It is still a point of debate whether Ardi was consistently using bipedal movement, as she had both opposable big toes and thumbs suited for climbing trees. Curved bones in her toes and divergent larger toe are not characteristic of a biped, and her pelvis shows evidence of muscles used in climbing, and therefore was a quadruped when moving around in trees. However, remains of her legs, feet, pelvis, and hands also suggest that she walked upright when on the ground.


          Field Notes from an Evolutionary Psychologist

          The following story is one I found on the wire and wanted to share with you.

          Why are gorillas in zoos dying from heart disease? Scientific sleuths now on the case.

          By TODD LEWAN
          AP National Writer

          Mopie looked the picture of ape fitness: His shoulders were broad and imposing, his silver-haired back sculpted and muscular, his biceps bulging as wide as a wrestler's thighs when he scratched his head.

          He had a healthy appetite (he'd put away 7 pounds of food daily) and Mopie was no couch gorilla either: He'd nimbly scale the mesh of his enclosures at the National Zoo in Washington, D.C., playfully chase the younger gorillas and perch himself high in an outdoor maple, as if to show the world he was the king of the Great Ape House.

          "The unique thing about Mopie was how extremely handsome he was," says Lisa Stevens, curator of primates and giant pandas at the National Zoo, and whenever the silverback sat, proudly, in the exhibit's trees, "it just added to his impressiveness."

          Which is why Stevens and the zoo's staff were so stunned when, on the afternoon of July 3, 2006, this prized western lowland gorilla suddenly collapsed after playing with some newly introduced mates. By the time the keepers cleared out the other gorillas and tried CPR on Mopie, the gentle, 430-pound giant was lifeless — a victim of heart failure at 34.

          Like his father, who had died the same way at the zoo in the early 1990s, Mopie had previously been diagnosed with an unexplained form of heart disease known as fibrosing cardiomyopathy, in which healthy heart muscle turns into fibrous bands unable to pump blood. And yet, he had not shown any outward symptoms, and his diet and behavior were normal.

          "There was nothing to indicate he was feeling poorly or under the weather," recalls Stevens. "That's what made it even more of a shock."

          No less troubling, two days earlier the National Zoo had lost its only other male group leader, a silverback named Kuja. Diagnosed just a month earlier with congestive heart failure related to cardiomyopathy, Kuja died while undergoing surgery to receive an advanced pacemaker. He was 23.

          Sadly, Mopie and Kuja were not alone.

          Gorillas in zoos around the nation, particularly males and those in their 20s and 30s, have been falling ill — and sometimes dying suddenly — from progressive heart ailments ranging from aneurisms to valvular disease to cardiomyopathy.

          Now zookeepers are scrambling to understand what factors may be causing the illnesses and what might be done to save the 368 lowland gorillas that currently reside in 52 zoos across North America.

          A 1994 study of 74 captive gorilla deaths, published by veterinarians Tom Meehan of the Brookfield Zoo in Chicago and Linda Lowenstine of the University of California at Davis, found that 41 percent — and 70 percent of males older than 30 — were from heart disease, mainly fibrosing cardiomyopathy.

          "That study was a wake up call," says Meehan, now the vice president for veterinary services at the Chicago Zoological Society. It showed the need to "go to the next level of evaluating the animals and figuring out how their lifestyle related to their health."

          In the mid-1990s, when the study was published, about 100,000 western lowland gorillas roamed freely within vast forests in Cameroon, the Central African Republic, the Republic of Congo, Equatorial Guinea, Gabon, Angola and Nigeria. Far less endangered than their relatives, the mountain gorillas, these apes were officially considered only as "vulnerable."

          Since then, however, lowland gorillas in the wild have been dying at an accelerating rate. Poaching, logging, a dramatic expansion in the trade of bushmeat, and outbreaks of Ebola have reduced their numbers to roughly 30,000 — and in September, the species was reclassified as "critically endangered."

          At their current rate of decline, the gorillas are projected to disappear from the wild by 2050.

          "Soon, these great apes may only exist in captivity," says Haley Murphy, director of veterinary services at Zoo New England, which runs Boston's Franklin Park Zoo and the Stone Zoo in Stoneham, Mass. The zoos are home to seven western lowland gorillas, the only species kept in captivity.

          In 2000, Murphy, together with Dr. Ilana Kutinsky, a cardiologist with the Michigan Heart Group, began reviewing cardiac ultrasounds of zoo gorillas in hopes of discovering why the animals were at risk for heart trouble. It was part of a broad, veterinary detective effort to help save what Murphy calls "our closest living relatives, evolutionarily."

          Problem was, no one had defined how a normal gorilla heart operated.

          But as ultrasound information was entered into a database and compared to necropsy reports on deceased gorillas , clues began to appear. "We started noticing that some gorilla hearts were grossly abnormal from others," Kutinsky says. "The abnormal ones were mildly enlarged, very thick, and weren't pumping as much blood."

          The findings raised more questions: Were the heart abnormalities the result of genetic differences? The gorilla's sex? Did climate play a role? How big a factor was diet? Were the gorillas getting enough exercise in their enclosures? Or too much? Was heart disease being caused by bacterial or viral infections?

          Some even asked: Were gorillas developing heart disease because of the way they were reared or socially grouped at the zoos?

          As the scope of the mystery widened, the number of cases of apes developing heart problems steadily climbed.

          One was Babec, a 24-year-old lowland gorilla at the Birmingham Zoo in Alabama. Male gorillas in zoos have lived to age 54, and median life expectancy is 30 so when Babec started coughing, eating less and clutching at his chest in early 2003, the staff veterinarians examined him, and identified his nemesis: cardiomyopathy.

          Although the gorilla was given medications for heart disease in humans, his condition kept deteriorating. He lost 80 pounds (20 percent of his body weight), was accumulating fluid in his abdomen. And by the summer of 2004, his heart pumped just 10 percent of the blood his body needed.

          With Babec in the final stage of heart failure, the zoo risked a procedure never before attempted on a gorilla : the implantation in Babec's chest of an advanced pacemaker that corrects the heart's electrical circuitry and restores its ability to contract properly.

          Today, Babec's prognosis is excellent. He's dropped the excess water weight, his heart and other organs work more efficiently, and his heart and pacemaker are continuously monitored.

          Neal Kay, a cardiologist at the University of Alabama at Birmingham's Heart and Vascular Center who volunteered to perform the operation, later remarked that the only reason Babec still greets visitors to the Birmingham Zoo is that "we got to him in time."

          Such intervention could save individuals like Babec — but still largely unaddressed were questions of why gorillas develop heart disease in the first place, and how to halt the disease's progression.

          That's why in November 2006 — three months after Mopie and Kuja died at the National Zoo — ape experts, human cardiologists, and zoo epidemiologists, pathologists and managers from around the country gathered at the Brookfield Zoo in Chicago to establish what they called the " Gorilla Health Project."

          Their first task: To build a National Gorilla Cardiac Database. With it, veterinarians could track rates of heart disease and death and try to learn why scar tissue was replacing cardiac muscle in apes.

          To Kristen Lukas, chair of the Gorilla Species Survival Plan for the Association of Zoos and Aquariums, the project marks "a sea change" in how zoos will care not only for gorillas, but a host of other endangered species in captivity.

          This level of networking between veterinary and human medical experts from universities, hospitals and animals rights groups "just never happened before," she says.

          Meehan, the Chicago veterinarian who has worked with gorillas since 1979, expects the initiative to bring animal care forward a quantum leap from, say, the 1960s, when gorillas were originally brought to North American zoos and staff struggled just to keep the captive population alive.

          Gathering new data will present challenges, of course. One is the need for echocardiograms of apes. To do the test, a gorilla must be anesthetized, "which carries a certain amount of risk," says cardiologist David Liang of Stanford University, a consultant to the Gorilla Foundation in California.

          Another option, some experts say, might be to perform biopsies on affected gorillas to obtain tiny samples of heart muscle. This, too, would require anesthesia.

          Many primatologists and veterinarians consider diet a prime suspect of heart disease in captive animals. And exploring that may require extensive study of the mortality of western lowland gorillas in the wild, they say — which, for many reasons, is tricky.

          Gorillas in the wild tend to die younger, meaning not as many live long enough for age-related disorders to show up. Moreover, male silverbacks — the king of gorilla society — often hide symptoms of illness because they fear they may be challenged by younger males.

          Still, research in the wild has paid off before. Not long ago, for example, it was learned that lowland gorillas, which are primarily herbivores, wade into swampy lake areas and eat vegetation growing underwater.

          "There was no way of knowing that sort of thing was happening until somebody went out there to Africa and noticed what the gorillas were doing," says primatologist Joseph Erwin of the Foundation for Comparative and Conservation Biology in Needmore, Pa.

          Ellen Dierenfeld, a gorilla nutritionist at the St. Louis Zoo, says that a member of the ginger family, Aframomum melegueta, is a staple food of western lowland gorillas in their native environments.

          Some scientists say Aframomum is a powerful antibacterial, antiviral, antifungal and anti-inflammatory "natural drug," which may serve as a preventive medicine for the gorillas. But this and other native African plants are often not part of zoo gorillas' daily diets.

          The Gorilla Health Project's diet and other data should be gathered by early 2009, analyzed and shared later that year, says Pam Dennis, a veterinarian in charge of analyzing the information.

          "The important thing is that we're now working to prevent the diseases in the first place," says Dennis, an epidemiologist with the Cleveland Metroparks Zoo and Ohio State University.

          "We started out trying to figure out human health by studying animals. Now we're turning to our findings in humans to figure out how to treat animals," she says with a chuckle. "It's come full circle, which is sort of a beautiful thing."


          Watch the video: ΧΡΗΣΤΟΣ ΘΗΒΑΙΟΣ - Ο ΑΜΛΕΤ ΤΗΣ ΣΕΛΗΝΗΣ (May 2022).


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