They're considered to be human like hands. They have a thumb like humans which allows them to grip onto trees and maneuver better. It also helps them with their grip onto branches and trees because they rarely come down from up there, so they need to be able to grip tightly even a sleep. I would say it's natural selection due to evolution.
Ventilation is the process which the air moves in and out of the lungs. Diffusion is the movement of gases without the use of energy and or effort by the body. Hope this helps!:)
