Research showing how genes affect group loyalty and patriotism was published in the October 2005 issue of Nations and Nationalism, an academic journal of the London School of Economics.

Entitled "Ethnic nationalism, evolutionary psychology, and genetic similarity theory," it shows how genetic similarity provides "social glue" in groups as small as two spouses and best friends or in those as large as nations and alliances.

The evidence comes from studies of identical and non-identical twins, adopted and non-adopted children, blood tests, social assortment, heritabilities, family bereavements, and large-scale population genetics.