Behavior Genetics, Vol. 9, No. I, 1979
Familial Resemblance for Specific Cognitive Abilities J. C. DeFries, 1 R. C. Johnson, 2 A. R. Kuse, x G. E. McClearn, 1 J. Polovina, ~ S. G. Vandenberg, 1 and J. R. W i l s o n 1 Received 27 Apr. 1978--Final 2 Aug. 1978
Measures of familial resemblance (spouse correlations, regressions of offspring on midparent, single-parent~single-child correlations, and sibling correlations) are presented for members of the two largest ethnic groups tested in the Hawaii Family Study of Cognition. Median spouse correlations (corrected for differences in test reliability)for 15 individual tests of specific cognitive abilities are 0.15 and 0.12 for Americans o f European and of Japanese ancestry, respectively. With regard to the regressions o f offspring on midparent value, corresponding median values are 0.50 and 0.35. Results o f hierarchical multiple regression analyses, as well as the ordering of single-parent~single-child and sibling correlations, provide no evidence to support the hypothesis that spatial ability is influenced by a sex-linked, recessive gene. KEY WORDS: assortative mating; cognitive ability; heritability; familial resemblance; sex
linkage.
INTRODUCTION F a m i l i a l r e s e m b l a n c e is a function o f b o t h genetic and c o m m o n (betweenfamily) e n v i r o n m e n t a l influences. Thus " f a m i l i a l i t y " (familial r e s e m b l a n c e due to genetic factors, e n v i r o n m e n t a l factors, or both) is necessary, but not sufficient, evidence for the presence o f h e r i t a b l e variation. T h e p r i m a r y The results reported here are made possible by collaboration of a group of investigators (G. C. Ashton, R. C. Johnson, M. P. Mi, and M. N. Rashad at the University of Hawaii, and J. C. DeFries, G. E. MeClearn, S. G. Vandenberg, and J. R. Wilson at the University of Colorado) supported by NSF Grant GB-34720 and Grant HD-06669 from the National Institute of Child Health and Human Development, 1 Institute for Behavioral Genetics, University of Colorado, Boulder, Colorado 80309. Behavioral Biology Laboratory, University of Hawaii, Honolulu, Hawaii 96822. 23 0001-8244/79/0100-0023503.00/0 9 1979Plenum PublishingCorporation
24
DeFries, Johnson, Kuse, McClearn, Polovina, Vandenberg, and Wilson
objective of this report is to present evidence of familiality in the Hawaii Family Study of Cognition. In addition, previous family studies of specific cognitive abilities will be reviewed, and results of a new test of the hypothesis that spatial ability is influenced by a sex-linked, recessive gene will be described. PREVIOUS STUDIES The first family study of specific cognitive abilities was reported by Willoughby (1927) over half a century ago. A battery of 11 tests was administered to 141 children between the ages of 12.5 and 13.5 years and to members of their families ("about" 90 fathers, 100 mothers, and 280 siblings). Average familial correlations for the six verbal tests exceeded those for the five nonverbal tests for all parent-offspring combinations and for two of the three sibling comparisons. Since the average spouse correlations were identical for the two types of test (both 0.44), the greater parentoffspring and sibling resemblances for the verbal tests are not attributable to differential assortative mating. They must have been due to a higher heritability, a greater impact of between-family environmental influences, or both. Five years later, Carter (1932) reported the results of another large family study of specific cognitive abilities. Two vocabulary and four arithmetic subtests were administered to members of 108 complete family groups (both parents and one or more children over 12 years of age) and to 31 incomplete family groups. Subtest scores were then averaged, resulting in measures of vocabulary and arithmetic abilities which had reliabilities greater than 0.90. Familial correlations again tended to be higher for the verbal measure. In this study, however, the greater parent-child and sibling resemblances for vocabulary may have been due in part to a greater spouse correlation (0.21 vs. - 0.04). For the next 40 years, the focus of human behavior genetic studies of cognition was on measures of general intelligence. However, at least in part because of the results of twin studies (see Vandenberg, 1968), a resurgence of interest in the genetics of specific cognitive abilities has occurred. Williams (1975) recently obtained data (WISC subscale scores of sons, 10 years of age, and WAIS scores of their parents) from 55 families living in a major city in Western Canada. In general, familial resemblance was found to be greater for verbal tests (subscales 1-6) than for performance tests (subscales 7-11), and this difference was especially pronounced between the verbal and performance IQ aggregates. More recently, a major family study of specific cognitive abilities was reported by Loehlin et al. (1978). A battery of cognitive tests which sampled
Familial Resemblance for Specific Cognitive Abilities
25
the domains of verbal, numerical, perceptual speed, and spatial abilities was administered to 192 families in Tel Aviv, Israel. Complete data were obtained on both parents and two children at least 13 years of age. In contrast to the findings of previous studies, familial correlations for the verbal tests were not consistently higher than those for the nonverbal tests in this study. The primary objective of Loehlin and his associates was to test the hypothesis that spatial ability is influenced by a sex-linked, recessive gene. O'Connor (1943) had previously observed that only about 25% of females scored above the median of males on a test of spatial ability and that this resuIt was consistent with sex-linked, recessive inheritance. Stafford (1961) later reported parent-child correlations for a spatial test (Identical Blocks) which were also consistent with this hypothesis. Unlike the case of autosomal inheritance, the expected patterns of parent-child and sibling correlati6ns for sex-linked characters are a function of the sex of the family members. The expected pattern of parent-child correlations for sex-linked, recessive characters is as follows: T'FS ~ FMD ~ rMS : rFD
where F, M, S, and D are father, mother, son, and daughter, respectively. The parent-offspring correlations reported by Stafford (1961), as well as those subsequently obtained for various tests of spatial ability by several other investigators, are summarized in Table I. It may be seen that only the small study by Hartlage (1970) resulted in a pattern of correlations which closely approximates that reported by Stafford. In a detailed study of familial resemblance for performance on Raven's Progressive Matrices (a reasoning test which involves spatial ability) in Israel, Guttman (1974) found only one item with a parent-offspring correlational pattern consistent with the hypothesis of sex linkage. However, this one item did appear to involve spatial visualization. Yen (1975) has utilized sibling correlations to test the hypothesis that spatial ability is influenced by a sex-linked, recessive gene. In the case of sibling correlations, the expected pattern for sex-linked, recessive characters is as follows: rSD ~ r s s "( rDD
where S and D again symbolize son and daughter. Yen administered four tests of spatial ability (Spatial relations, Paper Form Board, Paper Folding, and Mental Rotations) to approximately 400 pairs of white siblings who were high school students living in the San Francisco Bay area. The sexlinked, recessive pattern of correlations was obtained for all measures except Spatial Relations.
26
DeFries, Johnson, Kuse, McClearn, Polovina, Vandenberg,and Wilson
o
% ,.c:
< r~
o
I
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0
I
9~ o
~
"~ e~
o
is the child's expected score, X1 is the child's sex (coded 1 or 2), X2 is the m o t h e r ' s score, X~ is the father's score, B1 is the p a r t i a l regression o f Y on X~ (a m e a s u r e o f the i m p o r t a n c e of the effect o f sex on the child's score), B2 is the p a r t i a l regression o f Y on X~ (a m e a s u r e of m o t h e r - c h i l d resemblance), etc., and A is the regression constant. A s indicated in the a b o v e model, the significance of m a i n effects, t w o - w a y interactions, and the t h r e e - w a y interaction is tested sequentially. ( I n t e r a c t i o n s are represented by p r o d u c t s o f variables from which m a i n effects and l o w e r - o r d e r interactions have been linearly p a r t i a l e d . ) Thus B~, B2, and B3 are e s t i m a t e d from Y, X~, X2, a n d )(3 during step 1; the p r o d u c t s X~Xz, X1X~, a n d X~X3 a r e a d d e d to the e q u a t i o n during step 2; and, finally, the p r o d u c t X~X2X3 is entered during step 3. The increm e n t to the squared m u l t i p l e c o r r e l a t i o n due to the products during this sequence is a t t r i b u t e d to the respective interactions and m a y be tested for statistical significance. T w o - w a y interactions are indicative o f a c o n d i t i o n a l relationship between Y and the two variables. F o r e x a m p l e , a significant B4 w o u l d indi-
Familial Resemblance for Specific Cognitive Abilities
39
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Familial Resemblance for Specific Cognitive Abilities J. C. DeFries, 1 R. C. Johnson, 2 A. R. Kuse, x G. E. McClearn, 1 J. Polovina, ~ S. G. Vandenberg, 1 and J. R. W i l s o n 1 Received 27 Apr. 1978--Final 2 Aug. 1978
Measures of familial resemblance (spouse correlations, regressions of offspring on midparent, single-parent~single-child correlations, and sibling correlations) are presented for members of the two largest ethnic groups tested in the Hawaii Family Study of Cognition. Median spouse correlations (corrected for differences in test reliability)for 15 individual tests of specific cognitive abilities are 0.15 and 0.12 for Americans o f European and of Japanese ancestry, respectively. With regard to the regressions o f offspring on midparent value, corresponding median values are 0.50 and 0.35. Results o f hierarchical multiple regression analyses, as well as the ordering of single-parent~single-child and sibling correlations, provide no evidence to support the hypothesis that spatial ability is influenced by a sex-linked, recessive gene. KEY WORDS: assortative mating; cognitive ability; heritability; familial resemblance; sex
linkage.
INTRODUCTION F a m i l i a l r e s e m b l a n c e is a function o f b o t h genetic and c o m m o n (betweenfamily) e n v i r o n m e n t a l influences. Thus " f a m i l i a l i t y " (familial r e s e m b l a n c e due to genetic factors, e n v i r o n m e n t a l factors, or both) is necessary, but not sufficient, evidence for the presence o f h e r i t a b l e variation. T h e p r i m a r y The results reported here are made possible by collaboration of a group of investigators (G. C. Ashton, R. C. Johnson, M. P. Mi, and M. N. Rashad at the University of Hawaii, and J. C. DeFries, G. E. MeClearn, S. G. Vandenberg, and J. R. Wilson at the University of Colorado) supported by NSF Grant GB-34720 and Grant HD-06669 from the National Institute of Child Health and Human Development, 1 Institute for Behavioral Genetics, University of Colorado, Boulder, Colorado 80309. Behavioral Biology Laboratory, University of Hawaii, Honolulu, Hawaii 96822. 23 0001-8244/79/0100-0023503.00/0 9 1979Plenum PublishingCorporation
24
DeFries, Johnson, Kuse, McClearn, Polovina, Vandenberg, and Wilson
objective of this report is to present evidence of familiality in the Hawaii Family Study of Cognition. In addition, previous family studies of specific cognitive abilities will be reviewed, and results of a new test of the hypothesis that spatial ability is influenced by a sex-linked, recessive gene will be described. PREVIOUS STUDIES The first family study of specific cognitive abilities was reported by Willoughby (1927) over half a century ago. A battery of 11 tests was administered to 141 children between the ages of 12.5 and 13.5 years and to members of their families ("about" 90 fathers, 100 mothers, and 280 siblings). Average familial correlations for the six verbal tests exceeded those for the five nonverbal tests for all parent-offspring combinations and for two of the three sibling comparisons. Since the average spouse correlations were identical for the two types of test (both 0.44), the greater parentoffspring and sibling resemblances for the verbal tests are not attributable to differential assortative mating. They must have been due to a higher heritability, a greater impact of between-family environmental influences, or both. Five years later, Carter (1932) reported the results of another large family study of specific cognitive abilities. Two vocabulary and four arithmetic subtests were administered to members of 108 complete family groups (both parents and one or more children over 12 years of age) and to 31 incomplete family groups. Subtest scores were then averaged, resulting in measures of vocabulary and arithmetic abilities which had reliabilities greater than 0.90. Familial correlations again tended to be higher for the verbal measure. In this study, however, the greater parent-child and sibling resemblances for vocabulary may have been due in part to a greater spouse correlation (0.21 vs. - 0.04). For the next 40 years, the focus of human behavior genetic studies of cognition was on measures of general intelligence. However, at least in part because of the results of twin studies (see Vandenberg, 1968), a resurgence of interest in the genetics of specific cognitive abilities has occurred. Williams (1975) recently obtained data (WISC subscale scores of sons, 10 years of age, and WAIS scores of their parents) from 55 families living in a major city in Western Canada. In general, familial resemblance was found to be greater for verbal tests (subscales 1-6) than for performance tests (subscales 7-11), and this difference was especially pronounced between the verbal and performance IQ aggregates. More recently, a major family study of specific cognitive abilities was reported by Loehlin et al. (1978). A battery of cognitive tests which sampled
Familial Resemblance for Specific Cognitive Abilities
25
the domains of verbal, numerical, perceptual speed, and spatial abilities was administered to 192 families in Tel Aviv, Israel. Complete data were obtained on both parents and two children at least 13 years of age. In contrast to the findings of previous studies, familial correlations for the verbal tests were not consistently higher than those for the nonverbal tests in this study. The primary objective of Loehlin and his associates was to test the hypothesis that spatial ability is influenced by a sex-linked, recessive gene. O'Connor (1943) had previously observed that only about 25% of females scored above the median of males on a test of spatial ability and that this resuIt was consistent with sex-linked, recessive inheritance. Stafford (1961) later reported parent-child correlations for a spatial test (Identical Blocks) which were also consistent with this hypothesis. Unlike the case of autosomal inheritance, the expected patterns of parent-child and sibling correlati6ns for sex-linked characters are a function of the sex of the family members. The expected pattern of parent-child correlations for sex-linked, recessive characters is as follows: T'FS ~ FMD ~ rMS : rFD
where F, M, S, and D are father, mother, son, and daughter, respectively. The parent-offspring correlations reported by Stafford (1961), as well as those subsequently obtained for various tests of spatial ability by several other investigators, are summarized in Table I. It may be seen that only the small study by Hartlage (1970) resulted in a pattern of correlations which closely approximates that reported by Stafford. In a detailed study of familial resemblance for performance on Raven's Progressive Matrices (a reasoning test which involves spatial ability) in Israel, Guttman (1974) found only one item with a parent-offspring correlational pattern consistent with the hypothesis of sex linkage. However, this one item did appear to involve spatial visualization. Yen (1975) has utilized sibling correlations to test the hypothesis that spatial ability is influenced by a sex-linked, recessive gene. In the case of sibling correlations, the expected pattern for sex-linked, recessive characters is as follows: rSD ~ r s s "( rDD
where S and D again symbolize son and daughter. Yen administered four tests of spatial ability (Spatial relations, Paper Form Board, Paper Folding, and Mental Rotations) to approximately 400 pairs of white siblings who were high school students living in the San Francisco Bay area. The sexlinked, recessive pattern of correlations was obtained for all measures except Spatial Relations.
26
DeFries, Johnson, Kuse, McClearn, Polovina, Vandenberg,and Wilson
o
% ,.c:
< r~
o
I
(j r~ C~
0
I
9~ o
~
"~ e~
o
is the child's expected score, X1 is the child's sex (coded 1 or 2), X2 is the m o t h e r ' s score, X~ is the father's score, B1 is the p a r t i a l regression o f Y on X~ (a m e a s u r e o f the i m p o r t a n c e of the effect o f sex on the child's score), B2 is the p a r t i a l regression o f Y on X~ (a m e a s u r e of m o t h e r - c h i l d resemblance), etc., and A is the regression constant. A s indicated in the a b o v e model, the significance of m a i n effects, t w o - w a y interactions, and the t h r e e - w a y interaction is tested sequentially. ( I n t e r a c t i o n s are represented by p r o d u c t s o f variables from which m a i n effects and l o w e r - o r d e r interactions have been linearly p a r t i a l e d . ) Thus B~, B2, and B3 are e s t i m a t e d from Y, X~, X2, a n d )(3 during step 1; the p r o d u c t s X~Xz, X1X~, a n d X~X3 a r e a d d e d to the e q u a t i o n during step 2; and, finally, the p r o d u c t X~X2X3 is entered during step 3. The increm e n t to the squared m u l t i p l e c o r r e l a t i o n due to the products during this sequence is a t t r i b u t e d to the respective interactions and m a y be tested for statistical significance. T w o - w a y interactions are indicative o f a c o n d i t i o n a l relationship between Y and the two variables. F o r e x a m p l e , a significant B4 w o u l d indi-
Familial Resemblance for Specific Cognitive Abilities
39
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