From word games to workout challenges to staying sober, tracking a streak has never been easier. How can we leverage that motivational power to keep from being totally derailed when a positive streak, inevitably, ends?

With some doppelgangers, there might be more to the idea than meets the eye. A team of Spanish scientists studied pairs of unrelated look-alikes and found that they not only bear a striking resemblance to each other, but also share significant parts of their DNA.

Bullies’ top tactic is social exclusion, also known as “relational aggression.” It involves shutting out peers from group activities and spreading false rumors about them.