Dt. Miller et al., MINIMAL CONDITIONS FOR THE CREATION OF A UNIT RELATIONSHIP - THE SOCIAL BOND BETWEEN BIRTHDAYMATES, European journal of social psychology, 28(3), 1998, pp. 475-481
We hypothesize that sharing a birthday is sufficient to create a unit
relationship. Two studies demonstrated that individuals cooperated mor
e in a prisoners dilemma game when their (fictitious) opponent shared
their birthday. They also reacted more negatively to betrayal and were
less sensitive to relative gains for self versus other. (C) 1998 John
Wiley & Sons, Ltd.