Nature or nurture: what makes a good reader?

Language is perhaps the most obvious species-typical skill that distinguishes humans from our nearest primate relatives. Language evolved in the distant past of our species, is found across all human cultures, and is the primary mechanism for communication and the transmission and evolution of culture.

Our genes predispose us to develop language and culture defines the language we learn. Reading however, is an artefact of culture, has a much more recent advent.

Today, the ability to read is unevenly distributed within and between cultures. In cultures where reading instruction is readily available to all, literacy rates are high. But the acquisition of reading does not come without significant effort. In North America, as many as one in five children will have difficulty learning to read. A smaller proportion will be unable to acquire fluent reading skill.

The skill deficits and their etiology in these reading disabled or dyslexic children have been well studied. It is known that reading disability has a significant genetic component: studies have estimated a greater than 50% heritability of reading disability. But what about typically developing children? To what extent do genes influence early pre-reading and reading skills? What about the influence of the environment? And whether reading difficulties arise from nature or from nurture, are there effective ways to intervene?

Both genetic and environmental factors influence reading

One recent study involving a large group of young twins cast some light on these questions. Twin studies are particularly useful to answer this type of question because identical (monozygotic) twins share 100% of their genetic material, but fraternal (dizygotic) twins share on average only 50% of their genetic material. When twins are reared together, they share many environmental influences. To the extent that the performance of a particular task by identical twins is more similar than that of fraternal twins, an inference of genetic influence can be made. Statistical procedures are used to calculate the heritability, or relative contribution of genes and the environment, of the skills under examination.

Stefan Samuelsson and collaborators examined phonological awareness, the ability to isolate and manipulate speech segments such as words within compound words (cow-boy), syllables, and rhymes; and rapid naming, simply the rapid naming of strings of colours or pictures, two pre-reading skills that have been consistently related to reading outcomes. They also examined print knowledge, vocabulary, verbal memory, and visual perceptual skills. Print knowledge, vocabulary, and verbal memory have also been associated with reading outcomes.

The Samuelsson study was conducted with1254 four- and five-year-old identical and fraternal twins, tested in Australia, Norway, Sweden, and the United States. The basic findings were that phonological awareness, verbal memory, and rapid naming were more affected by genes than shared environment, and vocabulary, grammar, and print knowledge were more affected by shared environment than genes. Phonological awareness and print awareness had a high shared-environment correlation, which was absent between rapid naming and print. The authors suggested that this could reflect an early reciprocal influence between phonological awareness and print awareness.

“This research confirms that reading abilities and reading disabilities are strongly influenced by both genetic factors and environmental factors,” says Dr. Maureen Lovett, Director of the Learning Disabilities Research Program at The Hospital for Sick Children. “The study is particularly impressive because it includes young children from three countries with different educational practices and different expectations about the time at which formal reading instruction should be introduced.” Dr. Lovett stresses that, “we should not interpret these results to mean that genetically at-risk children cannot become skilled readers. In fact, ample evidence exists demonstrating the extent to which effective early intervention can make a difference for at-risk children.”

The finding that print knowledge was strongly influenced by shared environment rather than genes is perhaps not surprising: it seems intuitive. In this study, shared book reading with parents and letter-based activities were correlated with print knowledge and with verbal ability and phonological awareness as well. The implication here is that pre-school education can enhance these pre-reading skills.

The authors conclude that whether individual difficulties learning to read are primarily influenced by genes or by the environment, proper compensatory environmental support is the only way to enhance the probability that reading skills we be adequately mastered. For those children who are experiencing difficulty primarily for genetic reasons, additional and continued supports will be required to minimize academic risk.

Early reading intervention can make a difference

The effectiveness and some limitations of a pre-school reading intervention were demonstrated by another study conducted by Barbara Hindson and collaborators. From among successive cohorts of pre-school children over a three-year period, the investigators identified 101 at-risk for reading difficulty children on the basis of one or both parents meeting criteria for reading disability. Sixty-eight age-matched children deemed not at risk also participated. Children received an extensive battery of pre-reading, reading, and language tests before and after an intensive reading intervention.

The reading intervention consisted of individual 30-minute sessions, either two or three per week depending on the child’s pre-school attendance schedule. The material and approach were based on a previously validated pre-reading programme called Sound Foundations, which focuses on teaching phoneme identification, for example sun and sail start the same and drum and broom end the same, and a structured book-reading session in which the child and reader discuss the meaning of the story and the child is encouraged to relate it to her own experience. Children were taught until they reached pre-set skill criteria.

The at-risk group required more sessions that the not-at-risk group to meet criteria; however, the authors found that the intervention was effective for both groups. Although both groups showed significant gains, the not-at-risk group improved more than the at-risk group in three areas: phoneme identity, letter knowledge, and concepts about print.

The children were given follow-up tests toward the end of their first year at school. The not-at-risk group performed better than the at-risk group on the tests administered, but it is important to note that the at-risk group was performing at grade level. The authors tentatively suggest that the intervention they received in the pre-school period acted as a protective factor, helping the at-risk group to meet grade expectations in reading.

Taken together, these studies contribute to the body of evidence that demonstrate the importance of early identification of children at risk for difficulty with reading acquisition and providing appropriate, intensive early intervention. Children who are at risk for primarily genetic or combined genetic and environmental influences are likely to require more intensive and sustained remediation. As Dr. Lovett points out, “this intervention should take the form of systematic, explicit, phonologically-based reading instruction that incorporates extra opportunities for practice and consolidation of skills and specific training to help the child generalize new skills to unfamiliar settings and materials.”