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.