Why Gorillas Are So Gentle

The Upside and Downside of Living on Leaves

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

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

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


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

How Much Protein Do Gorillas Get From Eating Leaves?

More Than Enough for a Human Being, and Even More Than Enough for a Pig!

Here’s a rather dry and technical article that describes the amount of “available protein,” as opposed to “crude protein,” in the foods that wild mountain gorillas eat.


The mountain gorillas in this study were getting more than enough protein, mainly because they were eating so many leaves. Although leaves are low in calories, a substantial proportion of those calories comes from protein. If gorillas eat enough leaves to get enough calories, the protein takes care of itself. A leafy diet is so rich in protein that the gorillas can afford to snack on some low-protein fruit.

Why Do Leaves Make Up So Much of a Wild Gorilla’s Diet?

Because Gorillas Are Big.

“Large mammalian herbivores, according to accepted ecological theory, may be expected to feed on abundant, low quality food as a result of the relationship between their body size, metabolic requirements, and gut capacity. … Abundant low quality food means nonreproductive plant parts, i.e., stems and leaves, because fruit and flowers are too ephemeral to provide a regular source of food in bulk for large animals. So, large herbivores ought to be folivorous in a broad sense, and usually are.”


In other words, big plant-eaters mainly eat leaves.