As they stepped, their feet fell close together ... that walked upright" makes it a celebrity species in the story of human evolution. Lucy's pelvis hints that she walked upright on two legs.

But, unfortunately, annoying extra molars aren't the only way evolution screwed us over. Narrator: All primates, including humans, have something in common: We have incredibly bony feet.

And yet, its humerus (an arm bone) is quite human-like. Characteristics of its tibia (a lower leg bone) indicate that A. anamensis walked on two feet. This species includes "Lucy," the 3.2 million ...