Table S2.

Offspring relatedness to their spouses and the number of offspring and spouses of parents

Consanguinity of Marriage	Male reproduction	Female reproduction
Offspring	Father’s offspring	Mother’s offspring
Low to Medium	$\overline{d}$ = 2.1 (0.49), $t=4.2$, $P<0.001$**	$\overline{d}$ = 1.02 (0.29), $t=3.9$, $P<0.001$**
Low to High	$\overline{d}$ = 0.94 (0.48), $t=1.97$, $P=0.05$	$\overline{d}$ = 0.54 (0.23), $t=2.3$, $P<0.02$
Medium to High	$\overline{d}$ =  − $1.15(0.58),t$ =  − $1.89,P$ = 0.049	$\overline{d}$ = 0.47 (0.30), $t$ =  − $1.59$, $P=0.11$
Overall	${\text{ANOVA}}_{2\text{,}569}$ $F=9.3$, $P<0.001$**	${\text{ANOVA}}_{2\text{,}683}$ $F=8.6$, $P<0.001$**
Sons	Father’s wives	Mother’s husbands
Overall	${\text{ANOVA}}_{2\text{,}115}$ $F=1.48$, $P=0.23$	${\text{ANOVA}}_{2\text{,}155}$ $F=0.47$, $P=0.62$
Daughters	Father’s wives	Mother’s husbands
Overall	${\text{ANOVA}}_{2\text{,}170}$ $F=0.09$, $P=0.91$	${\text{ANOVA}}_{2\text{,}229}$ $F=0.43$, $P=0.65$

$\overline{d}$ is the mean difference between the groups, t is the t statistic, *P <0.01, **P <0.001.