Pack Instinct

Years ago I read a study regarding how groups of people respond to fear. Whilst I can remember the information within the study I cant remember who performed it. If anyone knows based on the the following could you let me know?

We are not so removed from our hunter gatherer roots. One or two instincts still remain within us. For example if you put a group of people into a situation that induces fear. For example a haunted house. Each member of the group will be on edge, if a door slams there would be screams and then laughter. Why does this laughter occur? Well it has been theorised that this is a in instinctual response to fear. In laughing you are baring your teeth. Simple I know however the study I have yet to refind provided some fairly compelling evidence on this matter.

So next time you're with a group in a situation that is causing fear. Dont forget to bare your teeth.Of course it could just be that the laughter relieves tension.