[MUSIC PLAYING] - Research links biological factors such as brain structure and function with intelligence. Intelligence is correlated with larger brain volume. But it is also correlated with a larger number of neurons and a thicker outer cortex of the brain. 

Brain function is also a predictor of intellectual ability. The brains of people with higher intelligence process information more quickly. And they operate more efficiently. 

The fact that intelligence is this broad indicates that intelligence is not located in any one part of the brain. But that said, certain cognitive factors can be predictive of intelligence, for example, working memory capacity or the ability to mentally work with multiple pieces of information simultaneously, as well as cognitive control and planning. 

Many of these neural structures and functions that contribute to intelligence depend at least partially on genetic factors. In fact, studies suggest that genetic factors may have a greater impact on intelligence level than environmental factors. 

Twin studies have shown us that identical twins have more strongly correlated intelligence test scores than do fraternal twins. And broader family studies have demonstrated that people with strong genetic similarities are likely to have similar levels of intelligence. This is backed up by adoption studies, which show that the intelligence of adopted children tends to correlate more strongly with their biological parents than their adoptive parents. 

But these studies also tell us that genetics doesn't give us the whole picture. Twins raised in the same house tend to have more similar intelligence scores than twins raised separately, indicating that environment is playing a role. It is also clear that environmental factors like good nutrition and educational opportunities tend to optimize brain development and, therefore, intelligence. 

Perhaps more interesting is that while both biological factors and environmental factors play a role in intelligence, the environment impacts children more than adults. This is because the environment directly impacts brain development during childhood and adolescence. Intelligence becomes more stable over time once brain development ends. 

Nature and nurture also interact to predict outcomes. For example, a highly intelligent child may get more attention from teachers and extra enrichment opportunities than a child with less intelligence. These educational differences may enhance the initial biological differences. So slight differences in intelligence due to genetics can grow larger over time due to the environment. 

This also leaves us with some pretty serious issues to consider because studies show that malnutrition, poor education, and chronic stress can serve to impair brain development. Children living in poverty may also be more likely to be exposed to toxins such as lead, which can impair brain development, negatively impact language skills, social skills, intellectual ability, and basic coordination. This all adds up to the finding that children living in poverty tend to have lower intelligence than children living with more resources. 

But it doesn't have to be this way. Early educational experiences matter, especially for children living in poverty. Early intervention programs like Head Start, a government program for low-income families, can help optimize intellectual development by offering early childhood education, nutrition, and parental support. And longitudinal studies show that children who participate in Head Start get better grades and are more likely to graduate high school, attend college, and earn higher incomes later in life. 

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