Table 1.

The four decision situations and their underlying payoff-structures including percentages of trials in which subjects chose the left alternative in each condition separately for prosocials and proselfs (selfish participants).

Decision situation	Percentage of trials averaged across subjects (mean ± SD)
	Prosocials	Proselfs	t-value (p)
Pure self-interest (PSI) e.g., 10/6 4/6	94.1% (± 12.92%)	95% (± 12.11%)	−0.22 (0.829)
Efficiency (E) e.g., 16/10 4/6	95.5% (± 8.96%)	95% (± 12.53%)	0.14 (0.886)
Non-costly social (NCS) e.g., 6/10 6/4	90.3% (± 16.25%)	92.1% (± 12.7%)	−0.36 (0.724)
Costly social (CS) e.g., 4/10 10/6	19.6% (± 16.32%)	6.9% (± 10.94%)	2.79 (0.008)