Main Human cooperation is widespread but fragile, with long-term outcomes ranging from sustained cooperation to collapse 1 , 3 , 14 . Extensive research has identified factors that make cooperation more likely, such as the ability to communicate 2 , 15 , selective interaction 16 , 17 , observability of contributions or reputation 18 , 19 , 20 , and the opportunity to punish 21 , 22 . However, a question that remains disputed is why, even under favourable conditions, cooperation is dynamic and prone to decline 4 , 23 , 24 . It is now widely accepted that humans have heterogenous cooperative behaviours, with some effectively characterized as unconditionally self-interested, others unconditionally cooperative, and a majority as conditionally cooperative 25 , 26 , 27 . However, explanations diverge as to why groups consisting of such actor types often start out cooperating but decline over time.…