At the beginning of the twentieth century the sex ratio for South Africans di§ered markedly according to racial group. Those for white
South Africans remained almost invariable, with more boys than girls, while black South Africans had a clear majority of girls, a situation that
the literature has almost completely overlooked. This high proportion of black girls was also present in most sub-Saharan countries. The reasons
are still not completely clear. Sex ratios at birth show more births of boys than girls. Boysí mortality was higher than girlsí mortality. But that does not explain why the twentieth-century black sex ratio was much lower than the sex ratios of pre-industrial European countries. We test several possible complementary explanations. The anomaly was caused, we argue, by a combination of higher mortality of boys and a preference for girls