Scaling a rope tests human strength and endurance such that it would quickly weed out competitors on a game show like American Gladiators. For small primates? Not so much. Duke University researchers tested the climbing prowess of five different species of primate, ranging in weight from 0.4 to 3.1 pounds (0.2 to 1.4 kilograms), on the hanging-rope equivalent of a treadmill. After 15 to 30 minutes climbing at top speed, the primates' oxygen intake had barely budged relative to a brisk walk. And unlike walking, climbing did not exact an increasing oxygen toll depending on the animal's size—suggesting the biomechanics of the two forms of locomotion may fundamentally differ, the researchers report in a recent issue of Science. They say the findings suggest an advantage that early primates may have had over other tree-climbers: the ability to explore new arboreal environments without pooping themselves out.