Scarr-Rowe Effect: History
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In behavioral genetics, the Scarr-Rowe effect, also known as the Scarr-Rowe hypothesis, refers to the proposed moderating effect of low socioeconomic status on the heritability of children's IQ. According to this hypothesis, lower socioeconomic status and greater exposure to social disadvantage during childhood leads to a decrease in the heritability of IQ, as compared to children raised in more advantaged environments. It is considered an example of gene–environment interaction. This hypothesized effect was first proposed by Sandra Scarr, who found support for it in a 1971 study of twins in Philadelphia, and these results were replicated by David C. Rowe in 1999. A 2015 meta-analysis found the effect was predominant in the United States while less evident in societies with robust child welfare systems.

  • low socioeconomic status
  • child welfare
  • meta-analysis

1. Original Research

In Sandra Scarr’s original work, she outlines the methods behind the study of genetic and environmental variance, using data from the 1960 US Census tract to estimate Socioeconomic status (SES),[1] and the Iowa Tests of Basic Skills to study genetic and environmental variations across children from advantaged and disadvantaged populations. This study focussed on the heritability of IQ based on social class and race, with the social and racial groups being too variated to make generalisations between groups questionable. Across both races, the total variance was generally found to be greater in the groups of higher socioeconomic status. It is suggested that, while genetic factors are not as significant in determining aptitude in lower SES groups of either race, there is a larger variance in phenotypes among higher SES children.[2]

1.1. Limitations

One of the major limitations of Scarr’s original work is that the sample of twins is separated into same-sex and opposite-sex as opposed to monozygotic (MZ) and dizygotic (DZ). This greatly undermines the statistical strength of this study.[3]

2. Replication Research

2.1. Fischbein - 1980

Fischbein used data from a longitudinal study started from the Department of Educational Research at the Stockholm Institute of Education, with twins from 40 of the largest cities and towns in Sweden.[4] An estimation of Socioeconomic status (SES) was taken from the parents’ occupation and family income, and scores were gathered from the sample using a differential ability test (DBA) that included a verbal ability test, inductive reasoning test, and a clerical speed test.[5][6] The clerical speed test showed insignificant differences between the social groups. Heritability of all variables tested, including IQ, was significantly higher in the higher SES group compared to the lower SES group, which presented the lowest heritability.[7]

2.2. Rowe - 1999

David C. Rowe’s work looks at the influence of genetic and environmental factors specifically on the variation of verbal IQ, with data from the 1909 sibling pairs from the National Longitudinal Study of Adolescent Health. Parental education level was used as a moderator for this study. It was found that verbal IQ was highly heritable among children whose parents had a higher level of education, by being similar to the earlier studies of Fischbein and Scarr-Salapatek, this adds support to the hypothesis of variance in IQ heritability at different levels of socioeconomic status. It is acknowledged that the level of parental education is likely to be influenced by genetic factors, with higher-educated parents passing on a higher level of IQ.[8]

2.3. Additional Research

In 2003, Eric Turkheimer and colleagues replicated the effect in an analysis of the National Collaborative Perinatal Project. Medical, psychological, and SES data were collected for children at 8 months, 1 year, 4 years, and 7 years; at age 7 they completed the Wechsler Intelligence Scale for Children (WISC). The mothers’ SES data were collected at their registration in the study and again at the end of the 7-year study. The study found that the variance in IQ in relation to SES displayed a non-linear relationship, suggesting that children from low SES families may have environmental and genetic differences, and differences in poorer environments are likely to contribute more to variations in genetic outcome than differences in higher SES environments.[9]

McLloyd’s 1998 study looked at socioeconomic disadvantage and the impact it could have on child development as a whole, IQ being included. This provided a separation of socioeconomic disadvantage into two types of poverty: persistent and transitory, these were then compared to an advantageous socioeconomic status. Persistent poverty was shown to have the worst impact on IQ, as well as other aspects of child development when compared to transitory poverty and children who never experience poverty. This acknowledged the other variables that were likely to be associated with a low SES (for example chronic stress, harsh and inconsistent parenting, etc.).[10]

Application beyond the USA

While there have been many replications, the Scarr-Rowe effect has primarily been studied in United States samples[11] and has been less applicable in European samples; this is likely due to more even access to economic resources, including educational, limiting poverty.[12] In 2019, a study of German twins by Gottschling tested the heritability of cognitive ability at three mean age points – 11, 17, and 23 years old. It was found that, in the younger cohorts of 11 and 17, higher SES could be correlated with a significantly higher mean level of cognitive ability. This provides support for the original study during childhood and adolescence, although not to quite the same degree.[13]

The Scarr-Rowe Effect in Adulthood

The original theory hypothesises that higher SES will be associated with greater heritability of IQ, very few studies have addressed this interaction within adult populations.[14] Evidence from Gottschling’s 2019 study suggests that the influence of the SES of a family as a moderator for IQ heritability changes as people get older – with results showing the effect being less significant in adolescence and not shown present in adulthood.[15]

2.4. Contradictory Research

A 2015 meta-analysis found evidence of the Scarr-Rowe effect only in the United States, but no evidence of such an effect in Australia or Western Europe.[16] Turkheimer et al. (2015) similarly note that the effect has been replicated more in the United States than in other countries, and that even in the United States some studies have failed to replicate it. Based on their analysis of the Louisville Twin Study, they reported weak evidence for the hypothesis that was not statistically significant.[17] A 2016 study in Australia found no evidence for the Scarr-Rowe effect.[18] In 2017, a twin study with a very large sample of 24,620 twins and 274,786 siblings born and raised in the economically diverse US state of Florida also found no evidence of the Scarr-Rowe effect.[19] A 2018 study of 9,012 individuals found evidence for a slight to modest effect in children born in Wisconsin during the 1930s and 1940s.[20]

3. See Also

  • Intelligence Quotient
  • Behavioural Genetics

The content is sourced from: https://handwiki.org/wiki/Biology:Scarr-Rowe_effect

References

  1. Turkheimer, Eric; Haley, Andreana; Waldron, Mary; D'Onofrio, Brian; Gottesman, Irving I. (17 November 2016). "Socioeconomic Status Modifies Heritability of IQ in Young Children". Psychological Science 14 (6): 623–628. doi:10.1046/j.0956-7976.2003.psci_1475.x. PMID 14629696. https://doi.org/10.1046/j.0956-7976.2003.psci_1475.x. 
  2. Scarr-Salapatek, Sandra (1971). "Race, Social Class, and IQ". Science 174 (4016): 1285–1295. doi:10.1126/science.174.4016.1285. ISSN 0036-8075. PMID 5167501. http://www.jstor.org/stable/1733128. 
  3. Turkheimer, Eric; Haley, Andreana; Waldron, Mary; D'Onofrio, Brian; Gottesman, Irving I. (17 November 2016). "Socioeconomic Status Modifies Heritability of IQ in Young Children". Psychological Science 14 (6): 623–628. doi:10.1046/j.0956-7976.2003.psci_1475.x. PMID 14629696. https://doi.org/10.1046/j.0956-7976.2003.psci_1475.x. 
  4. Fischbein, Siv (1 January 1980). "IQ and social class" (in en). Intelligence 4 (1): 51–63. doi:10.1016/0160-2896(80)90006-9. ISSN 0160-2896. https://doi.org/10.1016/0160-2896(80)90006-9. 
  5. Fischbein, Siv (1 January 1980). "IQ and social class" (in en). Intelligence 4 (1): 51–63. doi:10.1016/0160-2896(80)90006-9. ISSN 0160-2896. https://doi.org/10.1016/0160-2896(80)90006-9. 
  6. Turkheimer, Eric; Haley, Andreana; Waldron, Mary; D'Onofrio, Brian; Gottesman, Irving I. (17 November 2016). "Socioeconomic Status Modifies Heritability of IQ in Young Children". Psychological Science 14 (6): 623–628. doi:10.1046/j.0956-7976.2003.psci_1475.x. PMID 14629696. https://doi.org/10.1046/j.0956-7976.2003.psci_1475.x. 
  7. Fischbein, Siv (1 January 1980). "IQ and social class" (in en). Intelligence 4 (1): 51–63. doi:10.1016/0160-2896(80)90006-9. ISSN 0160-2896. https://doi.org/10.1016/0160-2896(80)90006-9. 
  8. Rowe, David C.; Jacobson, Kristen C.; Oord, Edwin J. C. G. Van den (1999). "Genetic and Environmental Influences on Vocabulary IQ: Parental Education Level as Moderator" (in en). Child Development 70 (5): 1151–1162. doi:10.1111/1467-8624.00084. ISSN 1467-8624. PMID 10546338. https://doi.org/10.1111/1467-8624.00084. 
  9. Turkheimer, Eric; Haley, Andreana; Waldron, Mary; D'Onofrio, Brian; Gottesman, Irving I. (17 November 2016). "Socioeconomic Status Modifies Heritability of IQ in Young Children". Psychological Science 14 (6): 623–628. doi:10.1046/j.0956-7976.2003.psci_1475.x. PMID 14629696. https://doi.org/10.1046/j.0956-7976.2003.psci_1475.x. 
  10. McLloyd, Vonnie C. (1998). "Socioeconomic disadvantage and child development.". American Psychologist 53 (2): 185–204. doi:10.1037/0003-066x.53.2.185. https://doi.org/10.1037/0003-066X.53.2.185. 
  11. Gottschling, J.; Hahn, E.; Beam, C. R.; Spinath, F. M.; Carroll, S.; Turkheimer, E. (1 January 2019). "Socioeconomic status amplifies genetic effects in middle childhood in a large German twin sample" (in en). Intelligence 72: 20–27. doi:10.1016/j.intell.2018.11.006. ISSN 0160-2896. PMID 31435119.  http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=6703848
  12. Turkheimer, Eric; Horn, Erin E. (2014). "Interactions Between Socioeconomic Status and Components of Variation in Cognitive Ability" (in en). Behavior Genetics of Cognition Across the Lifespan (Springer): 41–68. doi:10.1007/978-1-4614-7447-0_2. ISBN 978-1-4614-7446-3. https://doi.org/10.1007/978-1-4614-7447-0_2. 
  13. Gottschling, J.; Hahn, E.; Beam, C. R.; Spinath, F. M.; Carroll, S.; Turkheimer, E. (1 January 2019). "Socioeconomic status amplifies genetic effects in middle childhood in a large German twin sample" (in en). Intelligence 72: 20–27. doi:10.1016/j.intell.2018.11.006. ISSN 0160-2896. PMID 31435119.  http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=6703848
  14. Bates, Timothy C.; Lewis, Gary J.; Weiss, Alexander (3 September 2013). "Childhood Socioeconomic Status Amplifies Genetic Effects on Adult Intelligence" (in en). Psychological Science 24 (10): 2111–2116. doi:10.1177/0956797613488394. PMID 24002887. https://doi.org/10.1177/0956797613488394. 
  15. Gottschling, J.; Hahn, E.; Beam, C. R.; Spinath, F. M.; Carroll, S.; Turkheimer, E. (1 January 2019). "Socioeconomic status amplifies genetic effects in middle childhood in a large German twin sample" (in en). Intelligence 72: 20–27. doi:10.1016/j.intell.2018.11.006. ISSN 0160-2896. PMID 31435119.  http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=6703848
  16. Tucker-Drob, Elliot M.; Bates, Timothy C. (February 2016). "Large Cross-National Differences in Gene × Socioeconomic Status Interaction on Intelligence". Psychological Science 27 (2): 138–149. doi:10.1177/0956797615612727. ISSN 0956-7976. PMID 26671911.  http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4749462
  17. Turkheimer, Eric; Beam, Christopher E.; Davis, Deborah W. (November 2015). "The Scarr-Rowe Interaction in Complete Seven-Year WISC Data from the Louisville Twin Study: Preliminary Report". Behavior Genetics 45 (6): 635–639. doi:10.1007/s10519-015-9760-4. ISSN 0001-8244. PMID 26497158.  http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4749455
  18. Bates, Timothy C.; Hansell, Narelle K.; Martin, Nicholas G.; Wright, Margaret J. (May 2016). "When does socioeconomic status (SES) moderate the heritability of IQ? No evidence for g × SES interaction for IQ in a representative sample of 1176 Australian adolescent twin pairs". Intelligence 56: 10–15. doi:10.1016/j.intell.2016.02.003. https://www.pure.ed.ac.uk/ws/files/24434026/Bates_etal_I_2016_When_does_socioeconomic_status_SES.pdf. 
  19. Figlio, David N.; Freese, Jeremy; Karbownik, Krzysztof; Roth, Jeffrey (2017). "Socioeconomic status and genetic influences on cognitive development". Proceedings of the National Academy of Sciences 114 (51): 13441–13446. doi:10.1073/pnas.1708491114. ISSN 0027-8424. PMID 29133413.  http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5754768
  20. Woodley of Menie, Michael A.; Pallesen, Jonatan; Sarraf, Matthew A. (December 2018). "Evidence for the Scarr–Rowe Effect on Genetic Expressivity in a Large U.S. Sample". Twin Research and Human Genetics 21 (6): 495–501. doi:10.1017/thg.2018.63. ISSN 1832-4274. PMID 30560766.  https://dx.doi.org/10.1017%2Fthg.2018.63
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