This study presents the assessment of inbreeding depression on the intelligence quotient among north Indian Muslim Children of school age. The Wechsler Intelligence Scale for Children (WISC-R)-74 was given to the children in both groups (50 each non-inbred and inbred of the first-cousin status), aged 6 to 11 years and from the same socio-economic status. The change of the mean follows genetic theory; however, the nature of the change in variance seems to be somewhat different.
PIP: The level of inbreeding depression on the intelligence quotient (IQ) of North Indian Muslim schoolchildren was assessed in a survey conducted in Aligarh. The 50 inbred children were products of marriages between first cousins; their mean age was 7.7 years (range, 6-11 years). A significant (p 0.001) negative association was found between inbreeding and score on the Weschler Intelligence Scale for Children (WISC-C). In addition, the weighted mean IQ of inbred children )88.4 + or - 1.37) differed significant (p 0.001) from that recorded among 50 noninbred controls of similar age and socioeconomic status (99.6 + or - 2.0). The group means for both verbal and performance IQ subscales differed significantly and in the expected direction between subjects and controls, but the lower variance recorded in the inbred group did not conform to genetic theory. However, data do not always demonstrate a clear trend of linear increase in phenotypic variance with inbreeding in human populations. Additional surveys in other populations and for various inbreeding levels are recommended.