A while back, in “People in the Future Will Not Look Like Brazilians”, Razib suggested that the great amalgamation will stall because those who are inclined to out mix will do so, taking with them their xenophilic dispositions. The suggestion prompted a commenter to question whether there was any evidence that preferences for (racial) endogamy had, as seemingly presumed by Razib’s argument, a non-trivial genetic component. Apparently, there has been very little genetically informed research on this or closely related topics. Nonetheless, I was able to locate eight studies based on five independent samples which provided heritability estimates for some measures of national, ethnic, or racial pride, preference, or prejudice. The study results are summarized in the table below.

Author Sample # Twins[a] Sex   A C E S[b] CovGE Error[c] Questions
Lewis et al. (2014)                      
Germany Jena Twin Study 452/336/87 Mixed Patriotism 0.29 0.09 0.62       [1]
      Mixed Nationalism 0.20 0.27 0.53       [2]
      Mixed Generalized Prejudice 0.38 0.00 0.62       [3]
Kandler et al. (2015)                      
Germany Jena Twin Study 226/255/87 Mixed Discriminatory intent 0.31   0.49 0.20     [4][d]
      Mixed Narrow Xenophobia 0.46   0.41 0.13     [5][d]
Weber et al. (2011)                      
U.S. Midus II 349/342 Mixed Racial Identification 0.27 0.00 0.73       [6][d]
          0.27   0.73        
      Mixed Racial Preference 0.28 0.09 0.63       [7]
          0.39   0.61       [d]
      Mixed Racial Marriage 0.52 0.02 0.46       [8]
          0.55   0.45       [d]
      Mixed (Race) Identity Strength 0.34 0.07 0.59       [9]
          0.42   0.58       [d]
      Mixed Ethnic Identification 0.40 0.00 0.60       [10]
          0.40   0.60       [d]
      Mixed Ethnic Preference 0.46 0.00 0.54       [11]
          0.46   0.54       [d]
      Mixed Ethnic Marriage 0.08 0.31 0.61       [12]
            0.37 0.63       [d]
      Mixed (Ethnic) Identity Strength 0.42 0.00 0.58       [13]
          0.42   0.58       [d]
Lewis and Bates (2014)                      
U.S. Midus II 149/190 Mixed Favoritism 0.47 0.06 0.48       [14]
Truett et al. (1992)                      
Australia ANHMRCTR 1233/751+907[e] Female Racial Prejudice 0.49 0.14 0.37       [15]
    567/352+907[e] Male Racial Prejudice 0.11 0.40 0.49       [15]
Martin et al. (1986)                      
Australia ANHMRCTR 3810 Mixed White Superiority 0.40 0.09 0.51       [16]
      Mixed Apartheid 0.43 0.05 0.52       [16]
      Mixed Mixed Marriages 0.33 0.12 0.55       [16]
Hatemi et al. (2010)                      
U.S. VA30K 14781 total Female Immigration 0.63 0.02 0.13 0.05 -0.23 0.39 [17]
      Female (racial) Segregation 0.37 0.01 0.19 0.08 -0.09 0.43 [17]
      Female (racial) Busing 0.34 0.05 0.20 0.03 0.00 0.39 [17]
      Male Immigration 0.46 0.02 0.15 0.09 -0.15 0.43 [17]
      Male (racial) Segregation 0.50 0.02 0.14 0.08 -0.24 0.50 [17]
      Male (racial) Busing 0.17 0.10 0.17 0.14 0.00 0.44 [17]
Orey and Park (2012)                      
U.S. MTR 356/240   Racial Positive Affect 0.18 0.00 0.82       [18]

[a]Number of Twins: MZ/DZ/Unmatched (zygosity undetermined)
[b]Social homogamy
[c]Measurement error, otherwise included in E
[d]Best fitting model
[e]907 opposite sex pairs included

[1]e.g., “I love Germany”; “I am not proud to be German” (4 questions; 5 point scale)
[2]e.g., “People who do not dearly support Germany and do not respect the culture should live somewhere else” (4 questions; 5 point scale)
[3]e.g., [Turks/ Poles/ Italians/ and Swedes] are “likeable–unlikeable”, “modest-arrogant”, “friendly-unfriendly” (7 “prejudicial” adjective pairs; 5 point scale)
[4]e.g., “[Poles] who are unemployed should get less support than unemployed German” (7 questions; 5 point scale)
[5]Not reported (11 items)
[6]”How closely do you identify with being a member of your racial group?” (1 question)
[7]”How much do you prefer your racial group?” (1 question)
[8]”How important is it to marry within your racial group?” (1 question)
[9]Composite scale based on the above 3 questions.
[10]”How closely do you identify with being a member of your ethnic group?” (1 question)
[11]”How much do you prefer your ethnic group?” (1 question)
[12]”How important is it to marry within your ethnic group?” (1 question)
[13]Composite scale based on the above 3 questions.
[14]Religious, ethnic, and racial favoritism composite score based on 9 questions.
[15]Not reported. (1 question; response: “agree,” “uncertain,” or “disagree”)
[16]”Yes” or “No” response to the word presented. (1 question)
[17]Not reported.
[18]Feeling thermometer score for (other) Whites minus average feeling thermometer score for Blacks, Hispanics, and Asians.


For racial endogenous marriage the h^2 was 0.33 to 0.55 depending on the sample and model (k= 2). For any type of national/ethnic/racial in-group favoritism or out-group derogation the h^2 ranged from 0.18 to 0.55 with a cross sample mean of about 0.35. With typically one to a few vague questions employed as indexes of ethnocentrism (broadly constructed), the reliability of the measures were undoubtedly low, leading to large error terms and consequently inflating the non-shared environmental components. Of the studies located, only for one, Hatemi et al. (2010), was error variance estimated; averaged across indexes, error variance accounted for about 40% of the total. Given the typical unreliability of the measures, reasonable corrections would likely raise the cross sample average h^2 to at least around 0.50, a value frequently found in the case of other social preferences. So it seems that “racists” are born that way — partly. Of course “racism” is not a unified entity either on the phenotypic or genotypic level. For example, in-group favoritism and out-group bias are different phenomena phenotypically (Aboud, 20003; Cameron et al., 2001: Bennett et al. 2004) and genotypically (Lewis et al. 2014). Whatever the case, it does seem that individual differences in expressed ethnic and racial preference have a non-trivial genetic basis, as we might have anticipated given that most social preferences do.

There are a number of potential pathways by which genes could influence such inclinations. For some, Razib’s deduction would be shaky. For example, were variations in the degree of expressed racial preference mediated in full by a dynamic or generalized group affiliation mechanism, then dispositions for racial endogamy would be dependent on the social processes, ones subject to change, which defined social identities. Racial preference would have a genetic basis only so long as race was constructed as an identity. In regards to this possibility, Lewis and Bates (2010) found evidence that ethnic and racial favoritism were underwritten both by a generalized mechanism and by group type specific ones. More specifically, they found that variance in different sorts of favoritism (religious, ethnic, and racial) was attributable both to common and specific factors, implying that ethnic and racial favoritism are not merely vehicles of a generalized mechanism. It is plausible then that racial preference has more sturdy genetic roots (than might otherwise be the case). This could be made sense of in light of evolutionary models which show that homophyly — ancestry-based or otherwise — is readily evolvable (Fu et al., 2012).

If so, such preferences might plausibly account for some of the common tendency for assortative mating on racial ancestry found in and out of mestizaje nations (for example: Burrell et al. 2009; Risch et al. 2009; Zou et al. 2015; Sebro et al., 2010; Guo et al. 2014; Domingue et al. 2014). Notably, Zou et al. (2015) found that in Puerto Rico this assortment was the strongest on genes that coded for facial morphology and that, owing to such tendencies, both Mexican and Puerto Rican spouses were effectively as related as third to fourth cousins would be in an unstructured population. Apparently, even in Brazilian futures panmixia (with respect to race) will go unrealized.


Aboud, F. E. (2003). The formation of in-group favoritism and out-group prejudice in young children: Are they distinct attitudes?. Developmental psychology, 39(1), 48.

Bennett, M., Barrett, M., Karakozov, R., Kipiani, G., Lyons, E., Pavlenko, V., & Riazanova, T. (2004). Young Children’s Evaluations of the Ingroup and of Outgroups: A Multi‐National Study. Social development, 13(1), 124-141.

Burrell, A. S., & Disotell, T. R. (2009). Panmixia postponed: ancestry-related assortative mating in contemporary human populations. Genome Biol, 10, 245.

Cameron, J. A., Alvarez, J. M., Ruble, D. N., & Fuligni, A. J. (2001). Children’s lay theories about ingroups and outgroups: Reconceptualizing research on prejudice. Personality and Social Psychology Review, 5(2), 118-128.

Domingue, B. W., Fletcher, J., Conley, D., & Boardman, J. D. (2014). Genetic and educational assortative mating among US adults. Proceedings of the National Academy of Sciences, 111(22), 7996-8000.

Fu, F., Nowak, M. A., Christakis, N. A., & Fowler, J. H. (2012). The evolution of homophily. Scientific reports, 2.

Guo, G., Wang, L., Liu, H., & Randall, T. (2014). Genomic Assortative Mating in Marriages in the United States.

Hailey, S. E., & Olson, K. R. (2013). A social psychologist’s guide to the development of racial attitudes. Social and Personality Psychology Compass, 7(7), 457-469.

Hatemi, P. K., Hibbing, J. R., Medland, S. E., Keller, M. C., Alford, J. R., Smith, K. B., … & Eaves, L. J. (2010). Not by twins alone: Using the extended family design to investigate genetic influence on political beliefs. American Journal of Political Science, 54(3), 798-814.

Lewis, G. J., & Bates, T. C. (2010). Genetic evidence for multiple biological mechanisms underlying in-group favoritism. Psychological science, 21(11), 1623-1628.

Lewis, G. J., & Bates, T. C. (2014). Common Heritable Effects Underpin Concerns Over Norm Maintenance and In‐Group Favoritism: Evidence From Genetic Analyses of Right‐Wing Authoritarianism and Traditionalism. Journal of personality, 82(4), 297-309.

Lewis, G. J., Kandler, C., & Riemann, R. (2014). Distinct heritable influences underpin in-group love and out-group derogation. Social Psychological and Personality Science, 5(4), 407-413.

Kandler, C., Lewis, G. J., Feldhaus, L. H., & Riemann, R. (2015). The Genetic and Environmental Roots of Variance in Negativity toward Foreign Nationals. Behavior genetics, 45(2), 181-199.

Martin, N. G., Eaves, L. J., Heath, A. C., Jardine, R., Feingold, L. M., & Eysenck, H. J. (1986). Transmission of social attitudes. Proceedings of the National Academy of Sciences, 83(12), 4364-4368.

Orey, B. D. A., & Park, H. (2012). Nature, nurture, and ethnocentrism in the Minnesota Twin Study. Twin Research and Human Genetics, 15(01), 71-73.

Risch, N., Choudhry, S., Via, M., Basu, A., Sebro, R., Eng, C., … & Burchard, E. G. (2009). Ancestry-related assortative mating in Latino populations. Genome Biol, 10(11), R132.

Sebro, R., Hoffman, T. J., Lange, C., Rogus, J. J., & Risch, N. J. (2010). Testing for non‐random mating: evidence for ancestry‐related assortative mating in the Framingham heart study. Genetic epidemiology, 34(7), 674-679.

Truett, K. R., Eaves, L. J., Meyer, J. M., Heath, A. C., & Martin, N. G. (1992). Religion and education as mediators of attitudes: a multivariate analysis. Behavior Genetics, 22(1), 43-62.

Weber, C., Johnson, M., & Arceneaux, K. (2011). Genetics, personality, and group identity. Social science quarterly, 92(5), 1314-1337.

Zou, J. Y., Park, D. S., Burchard, E. G., Torgerson, D. G., Pino-Yanes, M., Song, Y. S., … & Zaitlen, N. (2015). Genetic and socioeconomic study of mate choice in Latinos reveals novel assortment patterns. Proceedings of the National Academy of Sciences, 201501741.