  Situations where people have to decide between hurting themselves or another
person are at the core of many individual and global conflicts. Yet little is
known about how people behave when facing these situations in the lab. Here we
report a large experiment in which participants could either take $x$ dollars
from another anonymous participant or give $y$ dollars to the same participant.
Depending on the treatments, participants could also exit the game without
making any decision, but paying a cost. Across different protocols and
parameter specifications, we provide evidence of three regularities: (i) when
exiting is allowed and costless, subjects tend to exit the game; (ii) females
are more likely than males to exit the game, but only when the cost is small;
(iii) when exiting is not allowed, altruistic actions are more common than
predicted by the dominant economic models. In particular, against the
predictions of every dominant economic model, about one sixth of the subjects
show hyper-altruistic tendencies, that is, they prefer giving $y$ rather than
taking $x>y$. In doing so, our findings shed light on human decision-making in
conflictual situations and suggest that economic models should be revised in
order to take into account hyper-altruistic behaviour.
