Do Assortative Mating Patterns for IQ Block Upward Social Mobility?

Wendy JohnsonUniversity of Edinburgh

William G. Iacono and Matt McGueUniversity 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

Correlations11-yo 17-yo

Midparent-twins IQ At 11 .480 At 17 .527 .440 At 25 .531Twins' IQ over time 11-17 .785 17-25 .807 11-25 .720Twins IQ by zygosity MZ at 11 .750 DZ at 11 .504 MZ at 17 .829 .809 DZ at 17 .517 .505 MZ at 25 .778 DZ at 25 .480Midparent IQ-ed .578 .571Midparent IQ-SES .513 .520Midparent ed-SES .739 .773Twins' IQ-midparent ed At 11 .316 At 17 .349 .326 At 25 .351Twins' IQ-SES At 11 .287 At 17 .334 .296 At 25 .331Mom-dad IQ .341 .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

1 2 3 4 5 6 7 8 9 10

10

20

30

Differences in Parental IQby Level of Higher-Parent IQ

Mean 17Mean 11SD 17SD 11

Decile of Higher-Parent IQ

IQ D

iffer

ence

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 Correlations11-yo MZ 11-yo DZ 17-yo MZ 17-yo DZ

Mid-Twin IQ-Difference in Twins' IQs At age 11 -.008 .068 At age 17 .115 .213 .191 .141 At age 25 .304 .240Difference in Parents' IQs-Mid-Twin IQ At age 11 .021 -.037 At age 17 .018 -.048 .047 .173 At age 25 .010 -.068Midparent IQ-Difference in Twins' IQs At age 11 .004 .073 At age 17 .050 .144 .056 .101 At age 25 .081 .132Difference in Parents' IQs-SESDifference in Parents' IQs-Midparent Education

.061 .097.092.032

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.0956-7976.2003.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.