  "Personal responsibility", one of the basic principles of modern law,
requires one to be responsible for what he did. However, personal
responsibility is far from the only norm ruling human interactions, especially
in social and economic activities. In many collective communities such as among
enterprise colleagues and family members, one's personal interests are often
bound to others' -- once one member breaks the rule, a group of people have to
bear the punishment or sanction. Such a mechanism is termed "joint liability".
Although many real-world cases have demonstrated that joint liability helps to
maintain collective collaboration, a deep and systematic theoretical analysis
on how and when joint liability promotes cooperation is lacking. Here we use
evolutionary game theory to model an interacting system with joint liability,
where one's losing credit could deteriorate the reputation of the whole group.
We provide the analytical condition to predict when cooperation evolves in the
presence of joint liability, which is verified by simulations. We also
analytically prove that joint liability can greatly promote cooperation. Our
work stresses that joint liability is of great significance in promoting the
current economic propensity.
