An Active Orangutan Burns Fewer Calories Than a Lazy Human

When an orangutan swings through the trees like an acrobat in its rainforest habitat, it's burning fewer calories than a human couch potato. A new study by biological anthropologist Herman Pontzer has found that oragutans use less energy, pound-for-pound, than any other mammal--except for that all-time champion of metabolic lethargy, the tree sloth.