In northeastern Ethiopia, scientists have spent over twenty years searching for fossils in the Ledi-Geraru research area. They recently discovered thirteen ancient teeth that have changed our understanding of human evolution. These teeth belong to at least two different hominin species that lived side by side millions of years ago. One species was an early member of Homo, our own genus. The other was a previously unknown species of Australopithecus that no scientist had ever discovered before. A team of more than twenty researchers from North America, Africa and Europe published these findings in the journal Nature. For many years, textbooks showed human evolution as a simple line from apes to modern humans. However, these new teeth show that evolution is much more complicated, like a bushy tree with many branches. The early Homo teeth are dated to 2.78 and 2.59 million years ago. The mysterious Australopithecus teeth are approximately 2.63 million years old. Scientists used volcanic ash deposits to date these fossils accurately. The new Australopithecus is different from Lucy, the famous skeleton discovered in the same region in 1974. Between three and two and a half million years ago, as many as four different hominin species may have lived in eastern Africa. They shared the same landscape and may have competed for food and water. Understanding these ancient teeth helps us learn about our distant past and how humans evolved in Africa.