What Factors Affect Intelligence

Intelligence is the capacity for learning.  The more intelligent you are, the more you can learn and potentially accomplish.  Human beings are complex and that makes generating a concise list of factors affecting intelligence difficult.  Some factors, like brain damage, have an immediate and measurable impact.  Other physical aspects, like heredity, birth order and nutrition, are less easy to quantify.  Education, overall health, and culture affect how well people can utilize their intelligence, but they don’t necessarily “change” intelligence.   

The precise way heredity and genetics plays a role in intelligence isn’t entirely understood, in part because genetic theories often spawn controversy.  In 1969, Arthur Jensen published an essay in the “Harvard Educational Review” presenting “evidence that racial differences in intelligence test scores may have a genetic origin.”  In “The Bell Curve”, a book published in 1994, authors Richard Herrnstein and Charles Murray say that people with high IQs will produce intelligent children, while people with low IQs will produce less intelligent children.

Evaluating environmental influences on intelligence is like trying to unravel the Gordian Knot; it is next to impossible to tease apart one factor from another.  The population of lower economic classes have lower IQ scores compared to their more well to do counterparts.  The question is, did the poverty cause low intelligence or did low intelligence cause the poverty?

A well balanced diet, medical care and physical exercise all work together to produce an environment where potential can be recognized and children can thrive.  In addition, some research studies indicate that breast feeding can enhance a child’s intelligence.  A study by University of Illinois researchers states, “In humans, children who are breastfed have higher IQs than children not fed breast milk and this advantage persists into adulthood.”   

Ethnicity appears to have an effect on intelligence, but in reality, the impact is cultural.  In the United States, Japanese children tend to receive higher scores than other groups.  Within Japan itself, the Buraku, a Japanese minority group, consistently score lower on intelligence tests than the rest of their peers.  Outside of Japan, Buraku children receive scores more in line with other Japanese children.

Within families, birth order seems to have an effect.  A Norwegian study found that first born boys, on average, outscored their younger siblings on IQ tests, but only by two or three points.   

The most surprising factor that affects intelligence is that intelligence can change.  According to the American Psychological Association, “Believing you can get smarter can make you smarter”.  A research study conducted in 2002 compared two groups of seventh graders.  “During the first eight weeks of the spring term, these students learned about the malleability of intelligence by reading and discussing a science-based article that described how intelligence develops. A control group of seventh-grade students did not learn about intelligence’s changeability, and instead learned about memory and mnemonic strategies.  As compared to the control group, students who learned about intelligence’s malleability had higher academic motivation, better academic behavior, and better grades in mathematics.”  In other words, the children who learned they could get smarter made themselves smarter!

Intelligence is a facet of the mind that is not static.  There is a certain baseline of intelligence that humans are born with, but after that, they have the capability to refine what they have and make the most of it.