Group Dynamics

On the long drive to FL I started catching up on my backlog of "This American Life" podcasts.
One episode was about people who ruin it for the rest of us. The intro was about a study that proved that there are three personality types that can poison a group. They are so infectious that they erode any group they encounter. The types are: jerks, slackers, and depressives.
The intro also talked about studies that prove that a group is only as strong as its weakest link. An amazingly strong group member can not make up for an amazingly weak one.