Contents

11 June 2010
Vol 328, Issue 5984

About The Cover

Cover image expansion

COVER Rows of marching soldiers will risk their lives to defeat the enemy and protect their country during intergroup conflicts. This combination of self-sacrifice and aggression toward competing groups is known as parochial altruism. A Report on page 1408 reveals that this behavior is regulated by oxytocin, a short peptide produced in the hypothalamus and known to promote in-group trust and cooperation.[Photo: Fernando Bueno/Getty Images]