[wexbnfgd] Efficient walking

The upright bipedal gait of humans when walking on level ground is much more efficient than four-legged locomotion.  The effort required for four-legged locomotion on level ground is comparable to a human walking uphill.  (At what slope?)

Ice ages have happened.

Shoes were a bipedal human invention.

Therefore, a human can validly claim to have distant four-legged ancestors who had to walk uphill, both ways, through the snow, barefoot.