At the Last Supper, Jesus said, “For ye have the poor with you always . . .” (Mark 14:7, King James Version). New research in behavioral genetics has proven Jesus correct.

Two new articles on the genetics of socioeconomic status (SES) shows that a partial reason why some people are rich and others are poor is their genetic differences. Even if poverty is ameliorated through social programs, people are going to pass their genes on to their children, and economic inequalities will reproduced themselves again. As a result, society will always have poor people.

It is no surprise that SES is partially genetically influenced. Research on the heritability of income and SES has occurred for decades. The results indicate that in Western countries, about 40-60% of the differences in SES/income are due to genetic differences (Hyytinen, Ilmakunnas, Johansson, & Toivanen, 2019).

Two new articles shed light on this fact. Both go beyond establishing the genetic influence on SES and dig into what this means for individuals and societies.

Hill et al. (2019)

Hill et al.’s (2019) article documents the search for segments of DNA that are associated with income differences. They found a total of 149 loci–a huge increase from their 2 loci they had found in the past (Hill et al., 2016). That would be a major advance by itself, but the follow-up analyses are what makes this article special.

The research team not only identified portions of DNA that are correlated with income, but they investigated what biologically the genes they identified do. Hill et al. (2019), found that most of these genes were important in the structure and function of brain tissue, especially medium spiny neurons.

Another fascinating finding was that the majority of the genes that Hill et al. (2019) identified were also associated with intelligence. In fact, income and IQ had a genetic correlation of r = .69, which is huge for two traits that are not highly similar. This means that one of the reasons SES and IQ are correlated is because the same genes that make some people smarter also make them richer.

Intelligence was not the only relevant trait for explaining how DNA differences result in SES differences. Low neuroticism and good physical and mental health are also relevant. But these traits also share genes with intelligence.

There is still a big question remaining: How does DNA result in SES differences? DNA doesn’t go out and earn a paycheck. All it does is encode amino acids which are then used to make proteins for the body. No one is paid to make amino acids.

Hill et al.’s theory is that DNA does not directly make people rich or poor. Instead, DNA serves as a blueprint for a healthy brain, which then functions well, which causes some people to be smarter than others. Bright people then do well in school. In a modern economy, educated people get more prestigious, better paying jobs, and this is what causes the higher income for people with certain DNA variations. It is a plausible theory and explains why there is no direct effect from DNA to SES. Instead, it is an indirect link with a lot of links in its chain of causality. It is a highly plausible theory.

Finally, Hill et al. (2019) used DNA to calculate polygenic scores, which they then used to predict sample members’ household income. They found that these scores could be used to make predictions. However, the predictions are often extremely inaccurate and are not useful for practical purposes. This is still important, though, because the proof of concept is there. As more research is conducted, it will be possible to make better predictions of people’s SES based on their DNA.

Abdellaoui et al. (2019)

Abdellaoui et al. (2019) were also interested in SES differences and genes, but their focus was on regional inequality. They compared polygenic scores for educational attainment (i.e., how long someone stays in school) in different parts of the UK. They found that wealthier parts of the UK had more people with a greater propensity to stay in school, and economically depressed areas had a disproportionate number of people with a genetic propensity to leave school early.

Thus, regional SES differences are partially genetic in origin. Abdellaoui et al. (2019) believe that selective migration has occurred from poor parts of the UK to wealthier parts (generally the cities) for generations. The evidence in the article is pretty convincing. More educated sample members were more mobile, and the people who moved from coal mining areas (which are very poor parts of the country) to other parts of the UK had higher polygenic scores for both IQ and educational attainment than people who stayed in coal mining areas or who were born outside of those areas.

In other words, there is a brain drain occurring in the UK. Smarter and better educated people move away from their home towns. Who is left behind in poor areas? Generally, people who have a genetic propensity to drop out of school or have a below-average IQ. Other genetic differences exist in several important traits (body mass index, ADHD, bipolar disorder).

It is hard to know how long this selective migration has been happening in the UK. Abdellaoui et al. (2016) believe that this process has been happening since the Industrial Revolution. I think they are right. I also suspect that selective migration has been happening for generations in the United States and likely most other industrialized nations.

Implications

The implications from these two articles are clear: there will always be socioeconomic inequality because these differences are partially due to genetic differences. No environmental intervention will permanently fix inequality. This is true at the individual level (Hill et al., 2019) and the regional level (Abdellaoui et al., 2019). Social programs cannot permanently cure poverty, nor can they fix all of the root causes of income inequality.

But that does not mean that society shouldn’t help. Indeed, that’s what the rest of the sentence from the Gospel of Mark says: “. . . and whensoever ye will ye may do them good.” We cannot cure poverty permanently, but we can relieve suffering and ensure that people are healthy and taken care of, and it is good to do so.

References

Abdellaoui, A., Hugh-Jones, D., Yengo, L., Kemper, K. E., Nivard, M. G., Veul, L., . . . Visscher, P. M. (2019). Genetic correlates of social stratification in Great Britain. Nature Human Behaviour, 3, 1332-1342. doi:10.1038/s41562-019-0757-5

Hill, W. D., Davies, N. M., Ritchie, S. J., Skene, N. G., Bryois, J., Bell, S., . . . Deary, I. J. (2019). Genome-wide analysis identifies molecular systems and 149 genetic loci associated with income. Nature Communications, 10, 5741-5756. doi:10.1038/s41467-019-13585-5

Hill, W. D., Hagenaars, S. P., Marioni, R. E., Harris, S. E., Liewald, D. C. M., Davies, G., . . . Deary, I. J. (2016). Molecular genetic contributions to social deprivation and household income in UK Biobank. Current Biology, 26, 3083-3089. doi:10.1016/j.cub.2016.09.035

Hyytinen, A., & Ilmakunnas, P., Johansson, E., & Toivanen, O. (2019). Heritability of lifetime earnings. The Journal of Income Inequality, 17, 319-335. doi:10.1007/s10888-019-09413-x

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