Poverty (low socioeconomic status; SES) is clearly associated with poor academic and career success as well as higher rates of obesity and anxiety-related behaviors. Poor neighborhoods seem to predispose children to anti-social behavior, with crime correspondingly increasing. Finally, evidence increasingly reveals that the brains of children raised in poverty develop differently, which appears to contribute to the noted associations. However, these are correlations. Doing something about the problem requires causal evidence. Does poverty cause these costly problems?
The answer is complicated in that we cannot manipulate growing up in poverty, which is the only way to establish causality. However, the answer, “No, poverty is not causal,” seems obvious. Lowering the poverty level tomorrow is unlikely to do anything to children suddenly finding themselves “technically” above the poverty line. Moreover, many poor children are perfectly fine; low-SES apparently had no effect on their brain development or health, and scores of children in the poorest nations on earth are also fine.
Clearly, “something” more closely associated with poverty than wealth is causal. That “something” must be an environmental factor because the brain and body “building block genes” are probably the same among poor and wealthy populations (although research into this morally unappealing possibility continues; it is theoretically possible that genetic variation largely accounts for SES). However, a gene-by-environment (G x E) interaction could be involved. That is, “something” in the environment alters genetic “products” via epigenetic processes, and, perhaps, only some children have those “susceptibility genes.” Diet deficiencies due to food availability or poor choice as well as poor schools are obvious environmental candidates (and easily if not cheaply solved), but is that all?
There is growing evidence suggesting that stress is a causal factor in the link between poverty, poor cognitive capabilities, and physical health. We’ve known for years that stress is damaging to brain development and health (see McEwen, 2013), but what’s the source of stress among the impoverished? After all, rich and poor kids face roughly the same kind of stress emanating from their social circles, like bullying, feelings of inadequacy, and other stresses resulting from social status and natural hierarchies. Increased violence is more prevalent in poor communities, but that’s probably because poverty predisposes children to anti-social behavior…which simply brings us back full circle to the problem of poverty and brain development.
The most encouraging evidence comes from a growing body of research into stress caused by perceptions of inequality. Poverty is a state of mind. Excellent animal research, which can explore causation, supports the impact of perceived social inequality and the body’s stress response. Even if the poverty line were lowered tomorrow or all poor people were given money, the perception of social inequality would remain. The research linked below makes an outstanding contribution to that research. In their cross-sectional study, Parker and colleagues observed that low SES children had lower cortical thickness, which they further determined was attributable to genes involved in the hypothalamic-pituitary-adrenal (HPA) axis, the brain’s stress response circuit. G x E interactions noted above could account for variations among the poor.
Parker, N., Wong, A. P. Y., Leonard, G., Perron, M., Pike, B., Richer, L., … & Paus, T. (2017). Income inequality, gene expression, and brain maturation during adolescence. Scientific Reports, 7. http://www.nature.com/articles/s41598-017-07735-2