WHAT ACCOUNTS FOR THE MANNER IN WHICH PEOPLE GROUP THEMSELVES TOGETHER?

RESPONSE PAPER ON DAVIS BROOKS’ "PEOPLE LIKE US" IN THE BOOK ACROSS CULTURES BY SHEENA GILLESPIE & ROBERT BECKER
*WHAT ACCOUNTS FOR THE MANNER IN WHICH PEOPLE GROUP THEMSELVES TOGETHER?
*WHAT DOES HE IMPLY WILL OCCUR(OR IS OCCURRING) DUE TO THESE DIVISIONS?