At some point in the last 4 million or so years, our hominin ancestors climbed down from the trees and got grounded. The transition between arboreal and terrestrial was, like just about everything in evolution, gradual. For decades researchers have debated, often heatedly, which hominin species was the first to be fully bipedal, walking and running rather than climbing.

Today, great answers come in small packages: A rare, mostly-complete juvenile hominin foot reveals new and unprecedented