TWINNING RATES IN ADMIXED COSTA-RICAN POPULATIONS

The frequency of twinning in two admired Costa Rican groups of women f rom the Limon province was investigated. One group was self-classified as Black, and the other group was self-classified as White. The twinn ing rate for each group was computed as the number of twin maternities divided by the total number of confinements multiplied by 1,000. Both groups have virtually identical twinning rates, even though Black sub jects were expected to have higher rates than White women. The twinnin g rate of both groups is higher than that in other New World admired B lack groups. This is particularly surprising for White females, whose European ancestral population is largely from Spain, the European coun try with the lowest twinning rate. The virtually identical twinning ra te is probably a result of the highly frequent gene flow between Black s and Whites in the population. (C) 1994 Wiley-Liss, Inc.