The discovery of a 2-million-year-old skull shows us once again how mysterious the origins of humankind are, even as it adds to our knowledge.

The flat-faced skull, with huge molars and a brain half the size of ours, was found in East Africa. It's human, but not from either of the human species already known to have existed at that time. Homo erectus, believed to be our direct ancestor, populated the region, as well as Homo habilis, a separate species of early humans.

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But only one skull similar to this new one has ever been found, in 1972. Legendary scientist Louis Leakey, not knowing what to make of that one, called it "indeterminate Homo."

The search for our origins is endlessly fascinating. Thanks to our big modern brains, we're well-equipped to enjoy it.