SSS 2009-07-28（在线收听）

Why did the orangutan cross the forest canopy? Presumably, to reach some tasty fruit. But the better question might be: how did the orangutan cross the forest canopy. And according to a study published in the Proceedings of the National Academy of Sciences, the answer is something of a surprise.

Large apes that spend a lot of time in the treetops face a major challenge in getting to their food: how can they maneuver their bulk over those spindly little outermost branches, which hold all the best fruit? Scientists had predicted that the best way to navigate the canopy would be to swing underneath the branches, or to crawl over them carefully with knees and elbows flexed.

But orangutans have a different approach. They like to mix it up. Sometimes they move upright, sometimes horizontally with their limbs fully extended. They avoid repetitive motions, which could make their perches sway even more precariously. And they tend to grab on to more than one branch at a time—a third of the time they’ve got hold of more than four at once. Which is good because the apple might not fall far from the tree, but an orangutan doesn’t want to fall at all.