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.

如果你的身体确实存在危险，比如一头公牛正在向你冲来，这些反应将可以挽救你的生命。但我们的身体也会释放皮质醇以应对情绪压力，在这种情况下，心率加快并没有多大好处，比如查看手机时发现老板发来的一封愤怒的邮件。

Scientists researching Alpine glaciers store ice in Antarctica. By analysing air bubbles in the ice they may be able to predict the future ...