Is it culture?

Last night the topic of corporate culture came up in my Operations class. As 'culture' as a term is used freely we tried to define it based on the team case studies we were reviewing for the day (the 1996 Mt Everest trajedy and a separate case on a disfunctional crewing team).
At question was whether you choose a culture as you would choose to play a game (willing participant that has self-selected to play). Or if the culture is defined and/or forced on you (you're born to it).

In class we determined that it was the latter. Today this same question, what is culture, has me thinking. What makes up the componants of culture? Is it self-manifested or predefined?  How much is nature and how much nurture?

As I look around the city I find myself questioning the basic elements of a pervasive structre. Wondering what pieces are necessary and which are irrelevant.