The age-old debate of nature versus nurture isn't really a debate. We've all pretty much agreed that when it comes to the complexity of raising a child, there are a large variety of factors that go into it. The debate really is the proportion of nature versus nurture in each aspect of someone's life.
Intelligence is one of the major factors that science has investigated. While there certainly seems to be some genetic factors linked to intelligence, we've also known for a long time that the environment is a big influence. One of these environmental factors can be poverty, or more specifically the income of parents. Previous work has shown that this can have effects on a child's brain development.
Now a recent study published in Nature examines this proposition, with the largest sample size to date. 1099 participants, from children all the way too young adults, had both their brain scanned and were given cognitive ability tests. Children from the lowest income bracket ($25,000 a year and under) had 6% less surface area on their brain, when compared to children from families that made over $150,000 a year.
That's extremely important because these outer regions of the brain are the cortex, and responsible for higher-level reasoning functions. Higher surface area results in that characteristic wrinkled shape we associate with the brain. A decrease in surface area is a sign of interrupted or stifled development. Other differences in brain structure were found, and were surprisingly dramatic between families that only made a few thousand dollars more or less than each other, among the poorest group in the study. The test scores also followed a similar trend.
There is also evidence that some of this damage is being done during development in the womb. It's unpublished yet, so not peer-reviewed, but the same team also did a study on one-month-old babies. To eliminate as many variables as possible, they scanned the brains of 44 African-American girls that were one month old, but from different socioeconomic brackets. There was again a definite link, with the poorer children generally having smaller brains. The hope is to follow these children for two years and look at their environment to see what factors are causing this lack of development.
Now this may all seem somewhat grim, but none of these studies have pinpointed exact causes yet. Some of the leading ideas though might lead to ways of alleviating this disparity. If a lower income families generally have poorer nutrition, it may be possible to supplement nutrition with programs. Another factor could be a lack of brain stimulating toys and a decreased ability to spend time with children, because the parents need to work more. Improving childcare programs for low income families could counteract this cause.
Still biology is definitely a factor, and not just genetics. Lower income families could generally be under more stress than high-income families. These stress markers would actually affect gene expression and overall physiology when a child is developing in the womb. But much more research will be necessary for all of these factors can be examined fully.
