从 南京南站 出发时，天色阴沉，铅灰色的云层压得很低，仿佛要将整座城市吞没。天气预报显示，一场罕见的 沙尘暴 正从 蒙古高原 南下，裹挟着黄沙与寒风，即将席卷华北。我攥着那张通往 太原 的高铁票，行李箱里塞满了防风衣、应急灯和 压缩饼干 ...

Modern life makes us tired, right? But research from societies in Africa and South America suggests people in the ancient world slept only 6.5 hours a night.