Climbing trees is no sweat for small primates, a new study reveals.
Squirrel monkeys, lemurs, and other tiny species use no more energy climbing vertically than they do walking on the ground. (Watch video.)
But large primates, including humans, tend to remain terrestrial for good reason.
"Larger primates have to pay a lot more in terms of energy to climb than to move horizontally," said study co-author Jandy Hanna, a biological anthropologist now at the West Virginia School of Osteopathic Medicine, who was a graduate student at Duke University at the time of the study.
"It's a lot of work for them to move around in a three-dimensional environment."
The study may support theories that the earliest primates were small, arboreal animals that eventually enjoyed a suite of advantages by adapting to live in trees.
A Rope to Nowhere
To determine the metabolic costs of climbing, researchers devised a novel way to measure the oxygen primates consumed as they climbed.
"We developed a vertical rope treadmill," Hanna said.
"Imagine a rope strung around two pulleys sitting one on top of another. The rope is moving down and the animal is climbing up to stay in place [on a section of rope] enclosed in a metabolic chamber."
The results revealed that primates burn energy while climbing at a rate that remains consistent with their body sizes.
But larger primates have a metabolic advantage when it comes to walking, which they do more efficiently than their smaller kin.
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