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By Ding Hong Zheng

Intelligence, like most aspects of human behavior and cognition, is a complex trait that is shaped by both genetics and environmental factors. As a general mental capability, it can be defined and measured in many different ways. Most definitions of intelligence involves the ability to learn from experiences and adapt from changing environments, ability to reason, plan, solve problems and think abstractly. It is not merely book learning or how well you do in school. Rather, it reflects a broader and deeper capability for comprehending our surroundings.

There are many studies conducted to search for the relationship between genetics and intelligence. Many of theses studies focused on the similarities and differences in IQ across family branches and members. For example, an analysis of twins from the Western Reserve Reading Project, conducted by Stephen A. Petrill, suggested that abilities may be differentially affected by genetic and environmental variation. The study focused on skills associated with reading: Phonological awareness, expressive vocabulary, and rapid automatized naming, as well as four reading outcome variables: Letter knowledge, word knowledge, phonological decoding, and passage comprehension. By using a sample of 283 twin pairs, they examined the genetic and environmental contribution to the stability of reading ability. During the experiment, twins were assessed across two different time periods. In Wave 1, twins were either kindergartener or first grader. Wave 2 assessments were conducted within one month after a year. The results of this study suggest that genetic influences accounted for a statistically significant portion of the stability among reading outcomes. Shared influences were also responsible for the stability in phonological awareness, expressive vocabulary, and letter knowledge.

The Western Reserve Reading Project shows that both genetic and environmental factors influence the reading outcomes of children and that the sibling similarity was greatest among monozygotic twins, followed by dizygotic twins. Although this experiment only focus on the reading comprehension of the twins but these skills can actually transfer to many different areas. For example, it can test the children’s ability to make connections, create visuals, and make inferences and predictions. Reading rewires your brain for greater intelligence and empathy. These could also be a form of intelligence that can help the children to thrive and succeed in the future.

Another study published in the journal Child Development finds that having strong reading skills as a child is a predictor for higher intelligence as they grew older. The researcher, Stuart J, Ritchie found that twins with better early reading ability than their identical sibling would not only remain better at reading as a young adult, but would also score higher on general intelligence tests. In addition, the twins in this study were brought up in the same family which allowed researchers to eliminate much environmental differences between the twins. Thus, the results of this study might imply that intelligence is mainly affected by genetic factors.

Genes make a substantial impact towards intelligence, but they are not the whole story. Environmental factors such as parenting styles, education, availability of learning resources, and nutrition all contribute to intelligence. A person’s environment and genes influence each other. Thus, although genetics play an important role in intelligence, the effects of environment still cannot be ignored.

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