Educability-and-Group-Differences-1973-by-Arthur-Robert-Jensen

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Between-Groups Heritability 145 could be accompanied by lowered within-group heritabilities. But the opposite relationship is more likely. It is much like the probabilistic but not necessary relationship between the number of years since a person’s birth and whether or not he is living or dead. If, in a city’s birth register, we look up a particular person, John Doe, and know only his birthdate, we can consult a life insurance company’s actuarial tables and determine the probability of living to the age of John Doe. The probability of living to John Doe’s age will be some value between 0 and 1. But no actuarial probability tables can help us in establishing that John Doe is in fact living or dead. The more years that have elapsed since his date of birth, the greater is the likelihood that we will be right if we assume (i.e., hypothesize) that John Doe is dead. We could always be wrong, but the likelihood of this decreases the greater the time elapsed since the birth of John Doe. And so it is with the likelihood of there being a genetic difference between subpopulations; the greater the heritability of a trait within groups, the greater is the likelihood that between-group differences in the trait involve genetic factors. But proof of the genetic hypothesis for any particular trait depends upon other evidence, just as proof that a particular John Doe is alive cannot b&proved by the actuarial tables. But if John Doe was born in 1870, how many of us would want to place our bet on the hypothesis that he is alive today Of essentially the same nature is our acceptance of the Watusi-Pygmy difference as genetic without formal proof. The same thing holds true, though to a lesser degree of likelihood, in the case of intelligence differences between social classes and racial groups. This valid limitation of generalizing heritability studies within populations to differences between populations is vigorously and correctly insisted upon by some writers (who, however, usually fail to point out the increasing likelihood relationship) while at the same time they show no hesitancy whatever about generalizing environmental sources of variance from one population to another. Hirsch (1970), for example, cites a study8 of mid-Eastern Jewish children in Israel brought up in a kibbutz who had IQs 30 points higher than similar children brought up in individual homes. Hirsch concludes: ‘There is no basis for expecting different overall results for any population in our species’ (Hirsch, 1970, p. 101). How does this differ from generalizing the heritability of intelligence from, say, Cyril Burt’s
146 Educability and Group Differences English samples to any other population in our species If a statement about genetic variance (h2) cannot be generalized across racial groups, how can Hirsch justify generalizing a statement about the effects on IQ of environmental variance, which is the complement of heritability, i.e., 1 —A2 If we cannot answer the question of the magnitude of the genetic component of social class or race difference in mean IQ, equally we cannot answer the question of the magnitude of the environmental component in these differences, for the two questions are in fact the same. Theoretically it is quite erroneous to say there is no relationship whatsoever between heritability within groups and heritability between group means. Jay Lush, a pioneer in quantitative genetics, has shown the formal relationship between these two heritabilities (Lush, 1968, p. 312), and it has been recently introduced into the discussion of racial differences by another geneticist, John C. DeFries (in press). This formulation of the relationship between heritability between group means (/*2) and heritability within groups (h2) is as follows: (1 ~r)p h2 h2 B ~ w (1 -p)r where hi is the heritability between group means; h^ is the average heritability within groups; r is the intraclass correlation among phenotypes within groups (or the square of the point biserial correlation between the quantized racial dichotomy and the trait measurement); p is the intraclass correlation among genotypes within groups, i.e., the wTithin-group genetic correlation for the trait in question. Since we do not know p, the formula is not presently of practical use in determining the heritability of mean group differences. But it does show that if for a given trait the genetic correlation among persons within groups is greater than zero, the between-group heritability is a monotomically increasing function of within-groups heritability. This is illustrated in Figure 5.1, which shows betweengroups heritability as a function of within-groups heritability for various values of the within-group genetic correlation when the mean phenotypic difference between the two groups involved is one standard deviation.
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Educability & Group Differences Art
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THE AUTHOR Since 1957 Dr. Arthur R.
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Ediicability and Group ^
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To the memory of Sir Cyril Burt e d
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List o f Tables 3.1 Correlations am
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17.3 Theoretical regression lines b
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2 Educability and Group Differences
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10 Educability and Group Difference
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1 4 16 24 16 ^ I 1 2 1 2 6 6 2 1610
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Subpopulation differences in educab
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2 Current technical misconceptions
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j Intelligence and educability Educ
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Table 3.1 Correlations (decimals om
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Table 3.3 Correlations (decimals om
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196 Educability and Group Differenc
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8 Multiple and partial correlation
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244 Educabilty and Group Difference
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14 Teacher expectancy Credence in t
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ig Physical environment and mental
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20 Recapitulation The study of abil
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Appendix on Heritability Heritabili
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References a in s w o r t h , m . d
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398 Author Index Davis, A., 300 Dea
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400 Author Index Nichols, R. C., 10
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Author Index 401 Warren, B. L., 120
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cultural deprivation, 258 culture-b
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Making Xs Test of speed and persist
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Stanford-Binet Intelligence Scale,
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