Table 1.

Contributor types broken down by cognitive taxation.

		Contributor type
Cognitive taxation	Selfish	In-group cooperator	Ambivalent parochial altruists	Strict parochial altruists
Yes (N = 49) No (N = 46)	1 (2%) 3 (7%)	12 (24%) 16 (35%)	35 (71%) 22 (48%)	1 (2%) 5 (10%)

Entries are observed number of subjects (row-based percentages in brackets). Selfish types keep their endowment; In-group cooperators contributed (>0) exclusively to the within-group pool; ambivalent aarochial altruists contributed (>0) to both the within- and between-group pool; strict parochial altruists exclusively contributed (>0) to the between-group pool.