Scientists say they have found a "remarkably complete" 3.8-million-year-old skull of an early human in Ethiopia, a discovery that has the potential to alter our understanding of human evolution. The skull, known as "MRD", was discovered not far from the younger Lucy, the ancient ancestor of modern humans, and shows that the two species may have co-existed for about 100,000 years. "MRD" could change how anthropologists view the critical point in the evolution of humanlike primates.