Down from the trees

We have seen that trees helped to facilitate the evolution of the opposable thumb, a key feature in the evolution of humans.   To this we can add some recent research that supports the hypothesis that trees have a played an important role in the evolution of bipedalism:

The debate over the origins of human bipedalism began during Charles Darwin’s lifetime and continues vigorously to this day, commonly dividing into two competing models, the researchers explained.

One model “envisions the pre-human ancestor as a terrestrial knuckle-walker, a behavior frequently used by our closest living relatives, the African apes,” they wrote in the PNAS report. The other model traces our two-legged walking to earlier tree-climbing, a mode of locomotion that is used by all living apes.

[…]

Altogether, the evidence leans against the idea that our own bipedalism evolved from a knuckle-walking ancestor, the pair wrote. “Instead, our data support the opposite notion, that features of the hand and wrist found in the human fossil record that have traditionally been treated as indicators of knuckle-walking behavior in general are in fact evidence of arboreality.”

In other words, a long-ago ancestor species that spent its time in the trees moved to the ground and began walking upright.

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