Valentine's Day is celebrated every year on Feb. 14. Here's when it falls this year, how it started, and why it's associated ...

Human newborns arrive remarkably underdeveloped. The reason lies in a deep evolutionary trade-off between big brains, bipedalism and the limits of motherhood.

Waiting for someone who is chronically late can be annoying—but what if their procrastination has hidden benefits? New research suggests it might.

Pew Research Center is a nonpartisan, nonadvocacy fact tank that informs the public about the issues, attitudes and trends shaping the world.