Some related concepts: http://en.wikipedia.org/wiki/In-group_favoritism http://en.wikipedia.org/wiki/Group_conflict http://en.wikipedia.org/wiki/Out-group_homogeneity http://en.wikipedia.org/wiki/Common_ingroup_identity And a couple of interesting experiments: http://lesswrong.com/lw/lt/the_robbers_cave_experiment/ http://www.news.wisc.edu/598
http://www.ncbi.nlm.nih.gov/pubmed/15491274
> Four experiments confirmed that women's automatic in-group bias is remarkably stronger than men's and investigated explanations for this sex difference, derived from potential sources of implicit attitudes (L. A. Rudman, 2004).
PDF: http://rutgerssocialcognitionlab.weebly.com/uploads/1/3/9/7/...