Team members have i) a common goal, ii) common responsibilities, iii) help each other out, iv) and have a structure to how they split their work.
I have heard of the term 'organic teams', i.e. teams that organize around these four attributes by themselves. My belief is that you will always require one team-role at minimum, i.e. a team lead, somebody that is responsible for the team itself, making sure that the four attributes above hold. The team lead does not have to be a dictator, i.e. setting the goal, responsibilities and structure, it could just as well be a facilitator that facilitates setting these attributes with the other team members.
