Table 1.

Various proximate mechanisms that ensure a reciprocal distribution of helping behaviour. These mechanisms are arranged from top to bottom from the least to the most cognitively demanding. Modified from de Waal and Brosnan (2006).

mechanism	catch phrase	definition
generalized reciprocity	‘Thank goodness!’	increased tendency to assist any others after having received assistance: no partner-specific contingency
symmetry-based reciprocity	‘We're buddies’	symmetrical relationship characteristics (e.g. association) prompt similar behaviour in both directions within a dyad without a high degree of contingency
attitudinal reciprocity	‘If you're nice, I'll be nice’	Parties mirror each other's social attitudes with a high degree of short-term contingency
calculated reciprocity	‘What have you done for me lately?’	scorekeeping of given and received favours resulting in partner-specific delayed contingency