This study presents the assessment of inbreeding depression on the ... inbred of the first-cousin status), aged 6 to 11 years and from the same socio-economic.
Behavior Genetics, Vol. 23, No. 4, 1993
Inbreeding Depression and Intelligence Quotient Among North Indian Children B a d a r u d d o z a I and M o h a m m a d A f z a l 1,2 Received 6 June 1991--FinaI ] Jan. 1993
This study presents the assessment of inbreeding depression on the intelligence quotient among north Indian Muslim Children of school age. The Weschler 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. KEY WORDS: Inbreeding depression; WISC-R; intelligence quotient; first cousins.
INTRODUCTION
mental assessment is being increasingly studied, even in the developing countries, to evaluate tile consequences of inbreeding among various population groups (Afzal and Sinha, 1983, 1984; Agrawal et al., 1984). Variations in the social and economic setups, coupled with different ecological conditions, can likely affect the outcome of inbreeding on mental traits among the individuals (Basu, 1985). However, generally a consistency is seen in the behavior of the performances of the inbred individuals on these IQ tests (Jensen, 1978). Such studies, despite their inherent limitations, can be referred to for studying inbreeding effects among humans (Afzal and Badaruddoza, 1990; Badaruddoza and Afza!, 1991). The present work, therefore, was undertaken in Aligarh (Uttar Pradesh), a major city in North India, noted for its educational and cultural institutions, in order to profile the level of inbreeding depression among North Indian Muslim children. The survey was conducted among Muslims of Aligarh for this purpose.
Certain mathematical deductions based on the genetical mechanisms underlying inbreeding effects, especially for quantitative traits, have served as models for characterizing various aspects of the phenomena (Crow and Kimura, 1970). Mather (1949) and Dickinson and Jinks (1956) have provided the basic models for studying the population genetics of quantitative traits subjected to known levels of inbreeding. The convention of searching for the presence or absence of inbreeding depression is not as comprehensive as searching for the change of the mean in either direction, be it depression or elevation. The direction of change may be exerted on either side for the recessive alleles. The absence of an inbreeding effect on the means indicates only the case of additive genes for a trait. If some loci are dominant in one direction, while some are in the other, their effects will tend to cancel each other and no inbreeding effect may be observed on the means, despite dominance at individual loci. As inbreeding continues, the genetic differences between homozygotes for different alleles become larger and genetic variance within the lines decreases, and in consequence, the total additive genetic variance increases (Wright, 1921; Li, 1955; Falconer, 1981). Inbreeding depression on
METHODS
Subjects. The subjects were chosen from two schools under the jurisdiction of the Muslim University, Aligarh, and situated in different areas in the city. All of them were Indians and Muslim males. The information on consanguinity was ascertained by the questionnaire and interview of the respective parents obtained by door-to-door visits. Only the
Section of Genetics, Department of Zoology, Aligarh Muslim University, Aligarh 202 002, U.P., India z To whom correspondence should be addressed.
343 0001-8244/93/0700-0343507.00/0 9 1993 PlenumPublishingCorporation
344
Badaruddoza and Afzal
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Fig. 1. Trend in the variation of mean IQs (verbal, performance, full-scale) among children of nonconsanguineous and consanguineous groups with their age.
Table I. Correlation (r) and Regression Coefficient (b) of Inbreeding and IQ Types of IQ Verbal Performance Full-scale *
Significant at p
r-+SE -
. 4 0 -+ . 0 8
b+-SE -
1 4 9 . 1 7 +_ 3 4 . 5 3 *
a 96.781
- . 4 8 _+ . 0 8
- 207.44
+- 3 8 . 3 0 *
103.98
- . 4 5 -4- . 0 8
- 1 8 7 . 5 7 -+ 3 4 . 6 3 "
99.76
.05). Mental Test. The WlSC (R)-74, which includes five verbal subtests (information, similari-
Figure i shows the probable linear relationship of IQ with age. A significant (p < .001) and negative correlation of IQ with inbreeding is found (Table I). The coefficients of linear regression (b) of the three IQs (verbal, performance and full-scale IQ) on inbreeding, as computed here, are also significant in each case, atp < .001. The distribution of IQ in the two samples, however, follows a more or less normal pattern (Table II), with weighted means of 99.6 -+ 2.0 and 88.4 _+ 1.37 among noninbred and inbred children, respectively, the difference being significant (p < .001). A similar trend is also found for both verbal and performance IQs
Inbreeding Depression and IQ
34S
Table II. Frequency Distribution of Subjects for Their IQs Among Noninbred (NI) and Inbred (IN) Groups (Percentage in Parentheses) Class, interval IQ
Verbal IQ
Performance IQ
Full-scale IQ
NI
IN
NI
IN
NI
60-69
--
--
5 (10.0) 9 (18.0) 15 (30.0) 15 (30.0) 5 (10.0) 1 (2.0) .
1 (2.0) 8 (16.0) 14 (28.0) 18 (36.0) 6 (12.0) 2 (4.0) 1 (2.0)
--
70-79
3 (6.0) 9 (18o0) 19 (38.0) 12 (24.0) 6 (12.0) 1 (2.0) --
80-89 90-99 100-109 110-119 120-129 130-139
.
.
140-above
--
--
Total
50
50
96.80
87.40
X• SE
•
Variance
1 (2.0) 7 (14.0) 15 (30.0) 10 (20.0) 11 (22.0) 4 (8.0) . 2 (4.0) 50 104.00
IN
12 (24.0) 14 (28.0) 2O (40.0) 3 (6.0) i (2.0)
--
3 (6.0) 10 (20.0) 15 (30.0) 11 (22.0) 7 (14.0) 2 (4.0) 2 (4.0) --
50
50
50
91.00
99.6
88.4
•
•
•
•
1.68
1.58
2.10
1.67
2.0
1.37
142.56
126.11
220.82
139.95
200.79
94.28
(analysis of covariance applied to the data yields similar results). The group means differ significantly in the expected direction but the variances do not. The lower variance in the inbred group is not in accordance with the prediction of genetic theory, although the differences are nonsignificant in the case of verbal and performance IQ (p > .05) but do reach significance cumulatively (full-scale IQ, p < .01) (Bartlett's chi-square test for homogeneity of variance, X 2 = 0.19, 2.25, and 6.79, df 1, for verbal, performance and full-scale IQs, respectively). The mean of the scores and average estimates of inbreeding depression per 10% F has been calculated for the individual subtests (Table III). A systematic indication of a linear effect of inbreeding depression thus is found for all the subtests.
DISCUSSION Despite the controversies related to the genetic predictions for IQ (Schwartz and Schwartz, 1974), there has been confirmatory data derived from many
different populations (B66k, 1957; Slatis and Hoene, 1961; Reed and Reed, 1965; Schull and N e d , 1965, 1972, Cohen et al., 1963; Adams and Neel, 1967; Carter, 1967; Neel et al., 1970; Seemanova, 1971; Bashi, 1977; Kamin, 1980; Jensen, 1983; Afzal, 1988), showing to some extent, inbreeding depression for intelligence. The present analysis which shows that the mean values of ai1 the components of IQ tend to decrease with inbreeding is in agreement with previous studies. The obtained values of negative correlations and coefficients of regression follow the same trend. The observed data, however, do show an exceptional decrease in variance in the inbred groups. This may not merely reflect sampling fluctuations. A similar nonsignificant increase in variance in the offspring of first cousins has also been observed by Slatis and H o e n e (1961) and Schull and Neel (1965). A reduction of variance in inbreeding has been found in certain other studies, i.e., Italian and Japanese children (Barrai et al., 1964; Niswander and Chung, 1965) although the data appear to be heterogeneous. In fact the
346
Badaruddoza and Afzal T a b l e III. Mean (M), Standard Error (SE), and Inbreeding Depression (ID) at
10% F of the Test Scores for Each of the Components of IQ Component of IQ
Mean -+ SE Noninbred Inbred
ID, 10% F
t*
Verbal Information Similarities Arithmetic Vocabulary Comprehension
9.62 +_ .40 7.52-- .39 15.08 _+ .37 5.48 _+ .30 11.10-+ .51
7.88 -+ .33 6 . 2 2 -+ .29 12.56 -+ .36 3.94 -+ .26 8.34-+ .49
5.57 4.16 8.06 1.54 8.83
3.35 2.67 4.88 3.87 3.90
Performance Picture completion Picture arrangement Block design Object assembly Mazes
1 4 . 7 4 _+ .43 8.40 +- .39 9.80--.39 7.72-+.48 11.82-+.70
11.72-+ .41 6.22 _+ .33 8.00 +- .33 5 . 1 6 -+ .33 9.98---.47
9.66 6.98 5.76 8.19 5.89
5.08 4.26 3.52 4.39 2.18
96.82 +- 1.71 104.00 +- 2.10 99.60 -_ 2.0
87.32-+ 1.48 91.00 +- 1.67 88.40 +- 1.37
30.4 41.6 35.84
4.20 4.84 4.62
IQs Verbal Performance Full-scale * p < .05.
precise estimation of the increase in genetic variance from the observed increase in phenotypic variance depends on how much environmental variance exists for a trait (Falconer, 1981). The expected change due to inbreeding is also rather small compared with the original variance. This renders exact detection rather difficult. Yet the trend of an increase in variance with inbreeding is suggested, and this has to be verified for various inbreeding levels and also in other populations. The empirical data do not always show a definite trend of a linear increase in the phenotypic variance with inbreeding in the human populations. The varying socio-economic status may also have some influence on inbreeding effects. However, this does not seem to hold true for Asian Muslim populations significantly, because more Muslims from higher socioeconomic strata marry among themselves, i.e., consanguineously. This practice is buttressed by the fact that the property of the woman often goes to the family of the husband she marries. ACKNOWLEDGMENTS
Thanks are due to Professor M. M. Agarwal, Chairman, Department of Zoology, for providing laboratory facilities. Financial assistance received from ICMR [Sanction No. 5/7/18/87(H.R.) IRIS 8702860] is gratefully acknowledged.
REFERENCES Adams, M. S., and Neel, J. V. (1967). Children of incest. Pediatrics 40:55-62. Afzal, M. (1988). Consequences of consanguinity or cognitive behaviour. Behav. Genet. 18:583-593. Afzal, M., and Badaruddoza (1990). A preliminary study on inbreeding effects on intelligence quotient profile among Sunni Muslims of Aligarh. Biol. Bull. Ind. 12:1-8. Afzal, M. and Sinha, S. P. (1983). Consanguinity effect on intelligence quotient and neonatal behaviours of Ansari Muslim children. Proc. Ind. Natl. Sci. Acad. B 46(5):407411. Afzal, M., and Sinha, S. P. (1984). Effect of consanguinity on intelligence quotient of Bihari Muslim Children. In Manna, G. K., and Sinha, U. (eds.) Perspectives in Cytology and Genetics; Vol. 4, pp. 114-117. Agrawal, N., Sinha, S. N., and Jensen, A. R. (1984). Effect of inbreeding on Raven matrices. Behav. Genet. 14:579585. Badaruddoza and Afzal, M. (1991). Inbreeding in human population. Man in India 2(4):431-453. Barrai, L., Cavalli Sforza, L. L., and Mainardi, M. (1964). Testing a model of dominant inheritance for metric traits in man. Heredity 19:651-668. Bashi, J. (1977). Effects of inbreeding on cognitive performance. Nature 226:440-442. Basu, S. K. (1985). Inbreeding in India, Its genetic consequences and implications in health care. In Population Genetics and Health Care; Issues and Future Strategies, NIHFW, New Delhi. B66k, J. A. (1957). Genetical investigations in a North Swedish population. The offspring of first cousin marriages. Ann. Hum. Genet. 21:191-221. Carter, C. O. (1967). Risk to offspring of incest. Lancet 1:436. Cohen, T., Block, N. Flare, Y., Kadar, M., and Goldschmidt, E. (1963). School attainments in an immigrant village. In
Inbreeding Depression and IQ
Goldschmidt, E. (ed.), The Genetices of Migrant and Isolate Population, Williams & Wilkins, Baltimore. Crow, J. F., and Kimura, M. (1970). An Introduction to Population/Genetics Theory, Harper & Row, New York. Dickinson, A. G., and Jinks, J. L. (1956). A generalised analysis of diallel crosses. Genetics 41:65-78. Falconer, D. S. (1981). Introduction to Quantitative Genetics, Oliver and Boyd, Edinburgh. Jensen, A. R. (1978). Genetics and behavioural effects on nonrandom mating. In Osborne, R. T., Noble, C. E., and Weyl, N. (eds.), Human Variation: The Biopsychology of Age, Race, and Sex, Academic Press, New York, pp. 51105. Jensen, A. R. (1983). The effects of inbreeding on mental ability factors. Personal. [ndiv. Diff. 4:71-87. Kamin, L. J. (1980). Inbreeding depression and IQ. Psychol. Bull. 87:469-479. Li, C. C. (1955) Population Genetics, University of Chicago Press, Chicago. Mather, K. (1949). Biometrical Genetics, Methuen, London. Neel, J. V., Schull, W. J., Yamamote, M., Uchida, S., Yanase, T., and Fujiki, N. (1970). The effects of parental consanguinity and Inbreeding in Hirado, Japan. II Physical development, tapping rate, blood pressure, intelli-
347
gence quotient, and school performance. Am J. Hum. Genet. 22:263-266. Niswander, J. D., and Chung, C. S. (1965). The effects of inbreeding on tooth size in Japanese Children. Am. J. Hum. Genet. 17:390-398. Reed, W. E., and Reed, S. C. (1965). Mental Retardation: A Family Study, Sounders, Philadelphia. Schull, W. J., and Neel, J. V. (1965). The Effects of Inbreeding on Japanese Children, Harper & Row, New York. Schull, W. J., and Neel, J. V. (1972), The effects of Parental consanguinity and inbreeding in Hirado, Japan. V. Summary and interpretation. Am. J. Hum. Genet. 24:425453. Schwartz, M., and Schwartz., J. (1974). Edivence against a genetical component to performance on IQ tests. Nature 248(5443):84. Seemanova, E. (1971). A study of children of incestuous matings. Hum. Here& 21:108-128. Slatis, H. M., and Hoene, R. E. (1961). The effect of consanguinity on the distribution of continuously variable characteristics. Am. J. Hum. Genet. 13:28-3t. Wright, S. (1921). Systems of mating. II. The effects of inbreeding on the genetic composition of a population. Genetics 6:124-143. Edited by H. Hill Goldsmith
