Two definitions that convey my ideas of bikers as a tribe:
-- A class or set of persons, esp. one with strong common traits or interests.
-- A group of people sharing an occupation, interest, or habit.
-- A unit of sociopolitical organization consisting of a number of families, clans, or other groups who share a common ancestry and culture and among whom leadership is typically neither formalized nor permanent.
(Tall bike crew of Yogya, Indonesia)
Charles Darwin himself observed, "A tribe including many members who... were always ready to aid one another, and to sacrifice themselves for the common good, would be victorious over most other tribes; and this would be natural selection." Darwin showed that the survival of the individual was responsible for evolution but recognized the key role of cooperation in this very survival.
Pelusi, Nando. "Clinging to Your Crew." Psychology Today 1 May 2007.
The commonality of biking makes the idea of Tribe accessible to many of those who feel that they can be apart of something more than just a usual group of friends. People find themselves in this situation by primarily being a young twenty-something or college students that shares common traits among peers. The idea of style and conformity do seem to play a role into the general make-up of these "tribes" or "crews", but to only a certain extent. Rebellion and the ideas of forward thinking also have strong presence in certain groups that unites them as a whole.