Figuring out the story of human origins is like assembling a huge, complicated jigsaw puzzle that has lost most of its pieces. Many will never be found, and those that do turn up are sometimes hard to place. Every so often, though, fossil hunters stumble upon a discovery that fills in a big chunk of the puzzle all at once — and simultaneously reshapes the very picture they thought they were building.

The path of just such a discovery began in November 1994 with the unearthing of two pieces of bone from the palm of a hominid hand in the dusty Middle Awash region of Ethiopia. Within weeks, more than 100 additional bone fragments were found during an intensive search-and-reconstruction effort that would go on for the next 15 years and culminate in a key piece of evolutionary evidence revealed this week: the 4.4 million–year–old skeleton of a likely human ancestor known as Ardipithecus ramidus (abbreviated Ar. ramidus).

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