Why The Ents Put Down Roots

Because once we started moving around, they could relax:

"The traditional theory of human origins states that we evolved to walk upright from ancestors who walked on all fours when on the forest floor. This new study suggests the opposite. Upright walking evolved in the ancestors of all apes, including humans, as a means of foraging for food in the small branches of the tropical forests and these techniques were later used by human ancestors to allow them to adapt to walking on two feet on the ground."