Who gets aggressive at late bars and why?

The exhaustive analysis in Steven Pinker's latest book shows that we are living in the most peaceable age for thousands of years. To anyone who spends time in late-night bars, this might come as a surprise. In these temples to hedonism, spilled drinks and unwelcome gropes all too often provoke violent brawls.

 A new study reported on our Research Digest set out to discover who gets aggressive in such environments and why.