Homo ergaster (shown in a museum display) was a small-brained but tall human species with body proportions similar to our own. Known largely from a 1.6-million-year-old fossil of a child found in 1984 near Lake Turkana, Kenya, the species is often called simply Turkana Boy.
Why it matters: Darwin hardly dared mention human evolution in On the Origin of Species. But the then shocking implication of his theory was obvious. Since the discovery of Java Man, the original "missing link," in the 1890s, the human family tree has grown rich with fossil evidence of species linking us to ancient apes.
Fred Spoor of University College London said that, whereas fossils of our earliest human ancestors "can very much be seen as apes who adopted a bipedal gait," Turkana Boy "is a true intermediate between modern humans and other primates."