Ardi could climb trees, using lengthy fingers and big toes for grasping, but she could also walk on the ground on two feet.  Walking with two feet on the ground and a reduction in the size of the canine teeth distinguishes this very first hominid from other apes.

Both of these characteristics provide clues as to what might have caused the last common ancestor to diverge from other apes.

The Making of Families, Not War

We now believe that social, instead of environmental, change, led to the species division. Natural selection involves reproductive success, so Ardipithecus males were probably pair-bonded to specific females, and may have aided them by gathering and carrying foods."

Such provisioning by males would have favored those males who could best walk on two feet, allowing them free hands for carrying food. Provisioned females could have "intensified their parenting" and carried their infants, which is easier to do in woodland environments when the forelimbs are free.

The reduction in canine teeth further suggests that Ardipithecus ramidus was not a meat eater.