A woman on the L train in New York City last week covers her face, fearful because a doctor with Ebola rode the train days earlier. Epidemiologists say people on the subway were not at risk. Stephen Nessen /WNYC hide caption

itoggle caption Stephen Nessen /WNYC

A passenger wearing a face mask arrives at Los Angeles International Airport Friday. Federal officials now require people traveling from West Africa to enter the U.S. at one of five airports equipped to screen them for signs of Ebola. Mark Ralston /AFP/Getty Images hide caption

itoggle caption Mark Ralston /AFP/Getty Images

Researcher Svante Pääbo, was able to extract a complete genome from this ancient human leg bone. Bence Viola/Max Planck Institute for Evolutionary Anthropology hide caption

itoggle caption Bence Viola/Max Planck Institute for Evolutionary Anthropology