Table 1.

Intra-class correlations for MZ, DZ same-sex, and DZ opposite-sex twin pairs for civic, work, welfare obligation and an omnibus summed measure of prosocial obligations.

	civic	work	welfare	prosociality
MZ male twin pairs	0.32	0.25	0.35	0.40
MZ female twin pairs	0.49	0.36	0.26	0.37
DZ male twin pairs	0.24	0.13	0.11	0.30
DZ female twin pairs	0.19	0.20	0.30	0.27
DZ opposite-sex twin pairs	0.06	−0.01	0.05	0.06