Abstract
THE few studies1,2 in which the effects of inbreeding on cognitive performance have been examined revealed that offspring of first-cousin marriages had lower IQ scores than offspring of unrelated parents. These studies were, however, performed in societies where the population engaging in such marriages is a small (1%, 6%)2,3 and unrepresentative proportion of the total population. Possible confounding of the effects of inbreeding with the effects of other intelligence-related variables such as socioeconomic status may lead the effects of inbreeding to be overestimated2. Unfortunately statistical control may either over- or under-correct for the correlates of the independent variables, leaving one in doubt about the true effect of inbreeding. I have now examined the effects of inbreeding on cognitive performance in an Arab population with a high rate of consanguinous marriage which minimised the distortions due to non-genetic variables. I show here that offspring of unrelated parents performed better than offspring of first-cousin marriages in intelligence and achievement tests administered at grades 4 and 6. The lowest level of performance and a higher variance were found for offspring of double-cousin marriages. The inbreeding depression found in this study is consistent and cannot be explained by the effects of socioeconomic status. I drew a nationally representative sample of 3,203 children in grades four and six (approximate ages 10 and 12 yr) of the Arab educational system in Israel. This sample constitutes about 10% of the total population in these grades and includes only normal (not retarded) children. Column 1 in Table 1 shows the division of the subjects according to grade level and consanguinity of the parents. A first-cousin marriage is between children of siblings. Children of first cousins have, on average, 1/16 pairs of genes by common descent. Double first cousins are children of siblings married to unrelated siblings. When they marry, their children have, on the average, 2/16 pairs of genes by common descent.
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References
Cohen, T., Block, N., Flum, Y., Kadar, M. & Goldschmist, E. in E. Goldschmist (ed.). The Genetics of Migrant and Isolated Populations (Williams & Wilkins, Baltimore, 1963).
Schull, W. J. & Neel, J. V. The Effects of Inbreeding on Japanese Children. (Harper and Row, New York, 1965).
Sterm, C. Principles of Human Genetics (Freeman, San Francisco and London, 1960).
Campbell, D. T. & Boruch, R. F. in Evaluation and Experience: Some Critical.(Issues in Assessing Social Programs (eds Lumsdaine, C. A. & Bennett, C. A.) Academic, New York, 1957).
Cavalli-Sforza, L. L. & Bodmer, W. F. The Genetics of Human Populations(Freeman, San Francisco, 1971).
Raven, J. C. Guide to the Standard Progressive Matrices. (Lewis, London, 1960).
MacLean, C. J., Morton, N. E. & Lew, R. Am. J. hum. Genet., 27, 365–384 (1975).
Morton, N. E. Am. J. hum. Genet. 26, 318–330 (1974).
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BASHI, J. Effects of inbreeding on cognitive performance. Nature 266, 440–442 (1977). https://doi.org/10.1038/266440a0
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DOI: https://doi.org/10.1038/266440a0
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