Do Assortative Mating Patterns for
IQ Block Upward Social Mobility?
Wendy Johnson
University of Edinburgh
William G. Iacono and Matt McGue
University of Minnesota
April 19, 2014
Assortative Mating for IQ
• Generally runs .3 to .4
• Source is most likely educational assortment
– Rather than IQ directly
– Increases genetic variance and population
stratification
• Generally assumed to be stable across the
range of IQ, but what if not?
– Interesting social phenomenon in own right
– Would especially stratify population where highest
Minnesota Twin Family Study
• Longitudinal study of two cohorts of twins
– One recruited age 11 (1260 pairs), one age 17
(635 pairs)
– Return basically every 3 years
– IQ assessed (abbreviated WAIS/WISC) ages 11, 17,
25 in twins, intake in parents
– Very population-representative; recruited from
population records with ~80% participation, high
retention over time
Correlations
Midparent-twins IQ
At 11
At 17
At 25
Twins' IQ over time
11-17
17-25
11-25
Twins IQ by zygosity
MZ at 11
DZ at 11
MZ at 17
DZ at 17
MZ at 25
DZ at 25
Midparent IQ-ed
Midparent IQ-SES
Midparent ed-SES
Twins' IQ-midparent ed
At 11
At 17
At 25
Twins' IQ-SES
At 11
At 17
At 25
Mom-dad IQ
11-yo
17-yo
.480
.527
.531
.440
.785
.807
.720
.750
.504
.829
.517
.778
.480
.578
.513
.739
.316
.349
.351
.287
.334
.331
.341
.809
.505
.571
.520
.773
.326
.296
.322
Another Correlation
• Higher parent’s IQ-absolute value of
difference in parents’ IQs:
– .515 in 11-yo
– .605 in 17-yo
• Some examples:
– 151-118, 151-110, 147-134, 146-121, 145-121,
145-121, 144-129, 143-100, 143-117, 142-105
– 77-77, 78-78, 78-76, 79-77, 80-74, 81-75, 81-79,
82-76, 83-81, 83-73, 84-72, 84-83, 84-80, 85-72
Differences in Parental IQ
by Level of Higher-Parent IQ
30
25
IQ Difference
20
Mean 17
15
Mean 11
SD 17
SD 11
10
5
1
2
3
4
5
6
7
Decile of Higher-Parent IQ
8
9
10
Why?
• Above 100, higher up you are, fewer there are
like you
– But people with high IQ tend to be successful at what
they’re doing and attractive partners to people in the
more heavily populated lower parts of the distribution
• Low IQs are relatively rare too
– But people in these ranges not so attractive to people
in more heavily populated parts of the distribution
– And less likely to participate in scientific studies
IQ and SES
Gibson, J. B. (1973). Journal of Biosocial Science, 5, p. 254,
Data from three Cambridge-based studies.
IQ and Earnings
Murray, C. (1997). Public Interest, 28, p. 23. Data from NLSY.
Social Mobility?
Murray, 1997
More Correlations
11-yo MZ 11-yo DZ
Mid-Twin IQ-Difference in Twins' IQs
At age 11
At age 17
At age 25
Difference in Parents' IQs-Mid-Twin IQ
At age 11
At age 17
At age 25
Midparent IQ-Difference in Twins' IQs
At age 11
At age 17
At age 25
Difference in Parents' IQs-SES
Difference in Parents' IQs-Midparent Education
17-yo MZ 17-yo DZ
-.008
.115
.304
.068
.213
.240
.191
.141
.021
.018
.010
-.037
-.048
-.068
.047
.173
.004
.050
.081
.073
.144
.132
.056
.101
.061
.032
.097
.092
Socioeconomic status modifies heritability of IQ in
young children
Author(s): Turkheimer, E; Haley, A; Waldron, M; et
al.
Source: PSYCHOLOGICAL SCIENCE Volume:
14 Issue: 6 Pages: 623-628 DOI: 10.1046/j.09567976.2003.psci_1475.x Published: NOV 2003
Times Cited: 302 (from All Databases)
Social Class, Solipsism, and Contextualism: How the Rich Are Different From the Poor
Author(s): Kraus, MW (Kraus, Michael W.)1; Piff, PK (Piff, Paul K.)2; Mendoza-Denton, R (Mendoza-Denton, Rodolfo)2; Rheinschmidt, ML
(Rheinschmidt, Michelle L.)2; Keltner, D (Keltner, Dacher)2
Source: PSYCHOLOGICAL REVIEW Volume: 119 Issue: 3 Pages: 546-572 DOI: 10.1037/a0028756 Published: JUL 2012
Times Cited: 0 (from Web of Science)
Cited References: 234 [ view related records ] Citation Map
Abstract: Social class is shaped by an individual's material resources as well as perceptions of rank vis-a-vis others in society, and in this article,
we examine how class influences behavior. Diminished resources and lower rank create contexts that constrain social outcomes for lower-class
individuals and enhance contextualist tendencies that is, a focus on external, uncontrollable social forces and other individuals who influence
one's life outcomes. In contrast, abundant resources and elevated rank create contexts that enhance the personal freedoms of upper-class
individuals and give rise to solipsistic social cognitive tendencies that is, an individualistic focus on one's own internal states, goals, motivations,
and emotions. Guided by this framework, we detail 9 hypotheses and relevant empirical evidence concerning how class-based contextualist and
solipsistic tendencies shape the self, perceptions of the social environment, and relationships to other individuals. Novel predictions and
implications for research in other socio-political contexts are considered.
Intelligence
Author(s): Sternberg, RJ (Sternberg, Robert J.)
Source: WILEY INTERDISCIPLINARY REVIEWS-COGNITIVE SCIENCE Volume: 3 Issue: 5 Pages: 501-511 DOI: 10.1002/wcs.1193 Published:
SEP-OCT 2012
Times Cited: 0 (from Web of Science)
Cited References: 72 [ view related records ] Citation Map
Abstract: Intelligence is the ability to learn from past experience and, in general, to adapt to, shape, and select environments. Aspects of
intelligence are measured by standardized tests of intelligence. Average raw (number-correct) scores on such tests vary across the life span
and also across generations, as well as across ethnic and socioeconomic groups. Intelligence can be understood in part in terms of the biology
of the brainespecially with regard to the functioning in the prefrontal cortex. Measured values correlate with brain size, at least within
humans. The heritability coefficient (ratio of genetic to phenotypic variation) is between 0.4 and 0.8. But genes always express themselves
through environment. Heritability varies as a function of a number of factors, including socioeconomic status and range of environments.
Racial-group differences in measured intelligence have been reported, but race is a socially constructed rather than biological variable. As a
result, these differences are difficult to interpret. Different cultures have different conceptions of the nature of intelligence, and also require
different skills in order to express intelligence in the environment.
100 Generations of Corn Breeding
Hill, W. G. (2005). Science, 307, 683 – 684, adapted from Dudley, J. W.,
& Lambert, R. J. (2004). Plant Breeding Reviews, 24, Part 1, 79.