Why did the hominin cross the plain? We may never know. But anthropologists are pretty sure that a smattering of bare footprints preserved in volcanic ash in Laetoli, Tanzania bear witness to an evolutionary milestone. These small steps, taken roughly 3.5 million years ago, mark an early successful attempt by our common human ancestor to stand upright and stride on two feet, instead of four.

Nearly 50 years ago, Neil Armstrong also took a few small steps. On the moon. His bootprints, al