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As the sole surviving species of the genus Homo, we Homo sapiens are one of the most taxonomically lonely species living on Earth today. But dig back a few thousand years or more and we find ourselves with plenty of company: Many now-extinct species shared the genus Homo, ranging from the robust Homo neanderthalensis, to the hobbit-like Homo floresiensis to the more primitive Homo habilis and Homoerectus. But do all these species, with their wide diversity of physical and cultural traits, actually belong in the same genus?

A 2.8-million-year-old jawbone fossil with five intact teeth unearthed in an Ethiopian desert is pushing back the dawn of humankind by about half a million years.