Echolocation is second nature to animals such as bats and dolphins. Can humans also find their way using sound as a tool? Ian Waldie/Getty Images hide caption

itoggle caption Ian Waldie/Getty Images

Johnson with her fellow researcher and sometimes husband, William Masters. The pair helped legitimize the study of human sexuality. AP hide caption

itoggle caption AP

It's busy down there: a gut bacterium splits into two, becoming two new cells. Centre For Infections/Science Photo Library/Corbis hide caption

itoggle caption Centre For Infections/Science Photo Library/Corbis