“Genetic and Environmental Variation in Educational Attainment: an Individual-Based Analysis of 28 Twin Cohorts”, Karri Silventoinen, Aline Jelenkovic, Reijo Sund, Antti Latvala, Chika Honda, Fujio Inui, Rie Tomizawa, Mikio Watanabe, Norio Sakai, Esther Rebato, Andreas Busjahn, Jessica Tyler, John L. Hopper, Juan R. Ordoñana, Juan F. Sánchez-Romera, Lucia Colodro-Conde, Lucas Calais-Ferreira, Vinicius C. Oliveira, Paulo H. Ferreira, Emanuela Medda, Lorenza Nisticò, Virgilia Toccaceli, Catherine A. Derom, Robert F. Vlietinck, Ruth Loos, Sisira H. Siribaddana, Matthew Hotopf, Athula Sumathipala, Fruhling Rijsdijk, Glen E. Duncan, Dedra Buchwald, Per Tynelius, Finn Rasmussen, Qihua Tan, Dongfeng Zhang, Zengchang Pang, Patrik K. E. Magnusson, Nancy L. Pedersen, Anna K. Dahl Aslan, Amie E. Hwang, Thomas M. Mack, Robert F. Krueger, Matt McGue, Shandell Pahlen, Ingunn Brandt, Thomas S. Nilsen, Jennifer R. Harris, Nicholas G. Martin, Sarah E. Medland, Grant W. Montgomery, Gonneke Willemsen, Meike Bartels, Catharina E. M. van Beijsterveldt, Carol E. Franz, William S. Kremen, Michael J. Lyons, Judy L. Silberg, Hermine H. Maes, Christian Kandler, Tracy L. Nelson, Keith E. Whitfield, Robin P. Corley, Brooke M. Huibregtse, Margaret Gatz, David A. Butler, Adam D. Tarnoki, David L. Tarnoki, Hang A. Park, Jooyeon Lee, Soo Ji Lee, Joohon Sung, Yoshie Yokoyama, Thorkild I. A. Sørensen, Dorret I. Boomsma, Jaakko Kaprio2020-07-29 (heritability)⁠:

We investigated the heritability of educational attainment and how it differed between birth cohorts and cultural-geographic regions.

A classical twin design was applied to pooled data from 28 cohorts representing 16 countries and including 193,518 twins with information on educational attainment [“years of education”] at 25 years of age or older.

Genetic factors explained the major part of individual differences in educational attainment (heritability: a² = 0.43; 0.41–0.44), but also environmental variation shared by co-twins was substantial (c² = 0.31; 0.30–0.33). The proportions of educational variation explained by genetic and shared environmental factors did not differ between Europe, North America and Australia, and East Asia. When restricted to twins 30 years or older to confirm finalized education, the heritability was higher in the older cohorts born in 1900^–₄₉1949_75ya (a² = 0.44; 0.41–0.46) than in the later cohorts born in 1950^–₃₉1989_35ya (a² = 0.38; 0.36–0.40), with a corresponding lower influence of common environmental factors (c² = 0.31; 0.29–0.33 and c² = 0.34; 0.32–0.36, respectively).

[The post-war reduction here might reflect the massive expansion in formal schooling & hollowing out of credentials, where crude education measures like ‘years’ hide the true differences in attainment.]

In conclusion, both genetic and environmental factors shared by co-twins have an important influence on individual differences in educational attainment. The effect of genetic factors on educational attainment has decreased from the cohorts born before to those born after the 1950s.