Climbing: A Cake Walk for Some Primates

Sensors on the treadmill measured the oxygen levels in the test chamber to determine how much energy was expended by the primate.

Timothy Griffin, a medical instructor at the Duke Medical Center's Orthopedic Bioengineering Laboratory and another leader of the study, said they found that for an animal weighing less than 500 grams (1.1 pound), "there was no difference" between walking and climbing, energy-use-wise.

Moreover, for the small primates weighing more than 500 grams, climbing was not significantly more demanding.

Humans' earliest primate ancestors, barely the size of large rats, evolved in special ways for life in the treetops, including developing grasping hands with nails instead of claws, Schmitt notes.

But, he said, they did not have to expend any more energy for the constant climbing, compared to walking on the ground.

"They were climbing up into the canopy and staying there. What we have shown is that they could have made this shift into a rich environment with insects and fruits without increased energetic cost," Schmitt said.

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