A replica of the pinky bone fragment found in a Siberian cave. Researchers used the bone bit to extract and sequence the genome of a girl who lived tens of thousands of years ago. Max Planck Institute for Evolutionary Anthropology hide caption

itoggle caption Max Planck Institute for Evolutionary Anthropology

Two men from northwestern Missouri became ill after tick bites infected them with a previously unknown virus. iStockphoto.com hide caption

itoggle caption iStockphoto.com

People walk in the storm surge from Hurricane Isaac along Lake Pontchartrain in New Orleans. Isaac was later downgraded to a tropical storm as it continued to grind its way through the Gulf Coast, dropping torrential rain and generating dangerous storm surges. Gerald Herbert/AP hide caption

itoggle caption Gerald Herbert/AP

A Beechcraft airplane sprays insecticide over Dallas early Monday morning to curb the spread of West Nile virus. LM Otero/AP hide caption

itoggle caption LM Otero/AP