In the segregated U.S. Army of 1918, the outbreak of Spanish Flu posed a particular problem. The faces of many victims darkened until, as an army doctor noted, it became “hard to distinguish the colored men from the white.” It’s one of the interesting items unearthed by British science writer Laura Spinney in her account of the pandemic that spread across every continent save Antarctica in 1918-19 and—by some estimates—killed nearly 5% of the world’s population. The virus didn’t originate in Spain (“an historical wrong set in stone,” she writes of the misnomer) but possibly at a U.S. Army basic training camp in Kansas; recruits leaving to fight in World War I might have spread the infection to the east coast and Europe. Pale Rider is weakest on how the flu “changed the world” but serves as a reminder of the greatest demographic disaster of the last century and perhaps all time. Could it happen again?