No Difference between Walking and Climbing for Small Primates

Duke University has shown in a recent experiment that small primates use up roughly the same amount of energy while climbing as they do while walking. The new finding could reveal why the tiny human ancestors chose to live a life in the trees more than 65 million years ago. The study involved five different species of primates, working their way on vertical and horizontal treadmills.

"We assumed it would be more energetically expensive for all of them to climb than walk, so this finding was unexpected. There's this longstanding assumption that it should cost more to go up", said Jandy Hanna, from the West Virginia School of Osteopathic Medicine, who was a student at Duke when the study was carried out.

Along with her colleagues, Hanna designed and built a climbing treadmill which had the ability of measuring the effort of the animal. The treadmill was placed in a special chamber that monitored the oxygen concentrations as the animal moved at the highest sustainable speed.

Although climbing does not take significantly more energy than walking for larger animals, it is clear that the energy spent during these activities decreases with size. As a result, primates weighting more than a kilogram are more inclined towards walking, while in small animals there is no difference, says Timothy Griffin, medical instructor at Duke Medical Center's Orthopaedic Bioengineering Laboratory.

It is widely believed that the period of transition to a life in the trees was critical to the development of our species. Daniel Schmitt, associate professor of biological anthropology at Duke, said that small primates, no larger than a rat, experienced an evolutionary change more than 65 million years ago which determined them to adapt to living on thin branches.

"Those changes included developing grasping hands with nails instead of claws. 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 added.