The yawning gap between the haves and have-nots will undoubtedly be a focus of discussion in this year’s midterm elections. But while the fact that income inequality has been growing is well known, little attention has been paid to how the changing nature of adolescence may be contributing to this troublesome trend.

In order to understand this connection, it’s important to understand why adolescence has become so much longer.

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It is often said that adolescence begins in biology and ends in culture — it starts with the onset of puberty and ends with the transition of young people into the traditional roles of adulthood: full-time employment, marriage (or its functional equivalent), and residential and economic independence from one’s parents.

Using these markers, it’s clear that this stage of life is significantly longer today than it has been before. The age of puberty has been falling, whereas the age at which people take on adult roles has been rising, and neither trend shows any sign of abating. By my estimate, adolescence, which in 1950 was approximately seven years long, now lasts around 15 years.

The earlier onset of puberty has been caused by multiple factors, the most important of which has been the well-documented increase in childhood obesity. But puberty has been accelerated by other factors as well: the presence of endocrine-disrupting chemicals in food, cosmetics and plastics; the increased survival of low-birth-weight infants, who go through puberty at a younger age than other children; father absence, which has been shown to hasten puberty in girls; and, some have speculated, children’s greater exposure to artificial light.

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Importantly, all of these contributors to early puberty are more often experienced by children from poor families. The most recent U.S. study, based on data from the mid-2000s, found that one-tenth of white girls and nearly a quarter of black girls, who are more likely to be poor than their white counterparts, had started developing breasts by age 7. That’s second grade.

Children who mature at a younger age are at significantly greater risk for all sorts of behavioral and psychological problems, including substance abuse, teen childbearing and delinquency — three impediments to success in school and in the labor force.

Early puberty also makes the adolescent brain more easily aroused — not just sexually, but in response to all sorts of exciting and pleasurable experiences. When this arousal occurs at an earlier age, it takes place long before brain systems that help teenagers control their impulses have fully developed. As a result, early puberty creates a longer gap between the activation of the brain’s “accelerator” and the maturation of its “braking system” — a gap that makes teenagers less able to delay gratification and consider the future consequences of their actions. This gap is wider, on average, for socioeconomically disadvantaged children, which exposes them to a longer period of vulnerability to impulsive decision-making.

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Unfortunately, as the transition from adolescence to adulthood has been prolonged, the ability to forgo immediate gratification for the prospect of a greater payoff in the future has become increasingly important. As has been widely reported, a college degree is now a requisite for a decent job; there are few economic advantages anymore to completing just a few years of college, even if one gets an associate’s degree along the way. Nowadays, though, the average undergraduate will need close to six years to complete what we continue to refer to as a “four-year degree.” That’s a lot of gratification to delay, especially for someone who has trouble doing so.

The ability to delay gratification is supported mainly by the development of prefrontal brain systems, which mature gradually from birth well into the early 20s, and which are highly susceptible to environmental influence. Advances in brain science are revealing the neural bases of self-control and helping to shed light on the neurobiological underpinnings of inequality.

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Children growing up in disadvantaged homes are far more likely at all stages of development to encounter experiences that impair prefrontal development, including poor nutrition and prenatal care; stress and trauma throughout infancy, childhood and adolescence; harsh and inconsistent parenting; and insufficiently stimulating schools. In contrast, children from more affluent backgrounds are far more likely to be born and to grow up under circumstances that are not only better in general, but especially so as far as prefrontal brain regions are concerned. It’s a familiar tale of the rich getting richer, and the poor getting poorer, except that in this case the riches are neural, rather than monetary.

Growing up poor has always imperiled young people's life chances, of course. But if adolescence were shorter, a relatively earlier puberty would be less of a problem (because the gap between puberty and the maturation of impulse control would be shorter), and the ability to delay gratification would be a less crucial capability (because better jobs would be available for those who weren’t willing or able to complete college).

The decline in the age of puberty can be halted, or perhaps even reversed, by public health policies that will lower rates of childhood obesity and limit our children’s exposure to endocrine disruptors. To the extent that exposure to artificial light is also a contributor to early maturation, parents should place limits on children’s screen time, especially in the hour before bedtime.

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Although there’s nothing we can (or should) do to make higher education less necessary for success in the labor market, we can help nurture the development of self-control and other capacities that help children learn to delay gratification. Research shows that raising children in a way that psychologists describe as “authoritative” (combining warmth and firmness) fosters better self-regulation, as do mindfulness meditation and physical exercise, two activities that can be encouraged both at home and in school.

The elongation of adolescence is only one of many contributors to income inequality, but at least there are things we can do to lessen its impact. With a social problem of this magnitude, any step, no matter how small, is worth taking.