among

(preposition): Denotes a mingling or intermixing with distinct or separable objects. (See Usage Note at amidst.)
(preposition): Denotes a belonging of a person or a thing to a group.
(preposition): Denotes a sharing of a common feature in a group.

How can you speak with authority about their customs when you have never lived among them?
He is among the few who completely understand the subject.
Lactose intolerance is common among people of Asian heritage.