First of all I will present the evidence that does support genetics having the most influence over a child’s reading ability – is it nature and therefore ability is predetermined at birth?
A study by Soden-Hensler found that twin studies have produced concordance rates – which is the likelihood of both members of a pair of twins having a certain characteristic – of between 30 and 60%; with print awareness and letter naming having a smaller genetic component than phonological awareness and decoding. Print awareness is the child’s acknowledgement that, for example, if an adult is reading a book they know that the speech is referring to the text on the page whereas phonological awareness includes the ability of identifying and manipulating units of oral language such as syllables. This evidence suggests that a less holistic approach is needed to explain reading ability.
Selzam used a genetic scoring technique and reading tests on over 5,000 children in the UK between the ages of 7 and 14 to predict children’s reading skills finding that DNA scores accounted for up to 5% of the differences between children’s reading skills. Furthermore, the link remained significant even after the children’s family socio-economic status was taken into consideration, implying that genetics may have a stronger influence over literacy and competency.
Christopher was part of a team who ran a cross-country twin study into individual differences in reading growth, using 500 pairs of twins from the US, 300 from Australia, and 300 from Scandinavia. Tests included having the children read out as many words and non-words in 45 seconds as they could. In all three samples, individual differences had significant genetic influences ranging from 0.3 to 0.85.
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However, results from studies that focus on genetic influence i.e. twin studies and heritability are not always 100% which implies that there is another influence at hand which could be an environmental influence – is it nurture and therefore ability is dependent on things like how many resources i.e. books are available to the child, or how often they are read to?
The Australian Early Development Index survey, or AEDI, assesses children at the beginning of their first year of school. They found that 13.9% of children in the lowest socio-economic quintile were assessed as being developmentally vulnerable in terms of their language and cognitive skills, compared to only 4.7% of children in the highest socio-economic quintile. Being “developmentally vulnerable” means that those children have a much lower than average ability in the aforementioned skills, therefore they may struggle with reading
Dr Sebastian Suggate conducted a study based on research in New Zealand, comparing the reading ability of 54 children who began learning to read from age 7 with 50 children who began learning to read from age 4. When they were tested at age 12, based on reading fluency and comprehension, Suggate found there to be no difference between the early and later starters. This research doesn’t rule out the influence of the environment, but provides evidence that the age at which a child starts formally learning to read may not have a large influence on later ability.
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It could be considered deterministic to say that reading ability depends purely on a child’s genetic makeup or their environment, at which point we could take an interactionist approach which takes into account both nature and nurture.
Turkheimer proposed that there is a gene-environment interaction that determines reading ability in children, whereby a child’s natural genetic potential for developing competence can be amplified or suppressed depending on the type of environment that the child learns in.
Samuelsson’s study involved measuring the spelling and reading ability of over 800 pairs of twins from the US, Australia, and Scandinavia at the end of kindergarten and again at Grade 1. They found that environmental effects only contributed significantly to individual differences before the children were exposed to formal instruction. However, genetic continuity was found between kindergarten and Grade 1 across all 3 samples.