Table 1.

Public good production does not necessarily require polyadic cooperation, and if it does, rarely encompasses all capable group members participating to the best of their abilities. Consequently, a collective action problem (CAP) can emerge amongst a subset (k), or all capable (N) individuals within a group. To distinguish between these two scenarios, throughout the text we speak of public good production by means of ‘joint’ versus ‘collective action sensu stricto’. Only if the latter occurs can a group be viewed as the primary unit of selection, or an emerging Darwinian individual [19]. N = all capable group members and 1 < k < N.

public good production
action	nindividuals	social dilemma	potential mechanisms
solitary	1	no	— kin selection — by-product mutualism
joint	k	possible	— kin selection — by-product mutualism — (pseudo-) reciprocity
collective (sensu stricto)	N	effectively overcome	— kin selection — by-product mutualism