Walking, climbing same for smaller simians

May 17th, 2008 - 3:29 pm ICT by admin  

Washington, May 17 (IANS) Walking or climbing is just the same for smaller simians, which may explain why these tiny ancestors of humans took to trees 65 million years ago. Researchers based their findings on the energy consumed by five different primate species while negotiating vertical and horizontal treadmills.

“We assumed it would be more energetically expensive for all of them to climb than to walk, so this finding was unexpected,” said Jandy Hanna on the West Virginia School of Osteopathic Medicine.

“There’s this longstanding assumption that it should cost more to go up,” she added.

Hanna had to design and build a novel climbing treadmill — essentially a loop of rope around two pulleys — to measure the animals’ efforts.

As the animals moved at their highest sustainable speed, sensors measured oxygen level changes within a chamber to derive the primates’ energy consumption.

While climbing was not significantly more demanding for heftier primates than lighter ones, “the energetic cost of walking decreased with size”, said Timothy Griffin, of Duke Medical Centre.

Consequently, species weighing more than half a kilogram may have more incentive to walk than to climb. But for those weighing less, “there was no difference”, he added.

The common assumption is that a transition to life in the trees helped lead to modern primates and our own up-right, two-legged walking.

Scientists think our earliest primate ancestors, just the size of large rats, underwent a number of fundamental changes as they adapted to moving and feeding on thin branches of trees 65 million years ago, said Daniel Schmitt, Duke associate professor who was Hanna’s doctoral dissertation advisor.

“Those changes included developing grasping hands with nails instead of claws,” Schmitt said. “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.”

The eight primates evaluated for energy consumption during climbing and walking were the slender loris, fat-tailed dwarf lemur, pygmy slow loris, Bolivian squirrel monkey and mongoose lemur.

The work appears in the May 16 issue of Science.

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