Genetic factors appear to influence individual differences in language development among children, at least in part, according to a study by British and American researchers. The study, which also found that environmental influences on children's language development were unique to the individual, not the shared environment, was published in the May/June issue of the journal Child Development.
Researchers from the Institute of Psychiatry in London, the University of Oxford, and the University of Missouri-Columbia in the United States investigated both individual differences in language development in the normal range and at the low end of ability in 4 1/2-year-old twins.
They recruited participants as part of the Twins Early Development study (TEDS), a longitudinal study involving a representative sample of all twins born in England and Wales in 1994, 1995 and 1996. It is the largest twin study to investigate diverse aspects of language, including articulation, phonology, grammar, vocabulary and verbal memory in a group of children of the same age. Opposite-sex twins were included in the study in order to explore sex differences in genetic and environmental influences for each individual measure.
"Children differ in the rates in which they acquire language and in their linguistic ability," explained lead researcher Yulia Kovas, a PhD student at the Institute of Psychiatry in London. "Understanding the sources of this variation is an important part of forming a comprehensive account of language development."
The study findings, she notes, are consistent with previous research showing that differences between children in different aspects of language development do not seem to be uniquely dependent on genes or environment.
"The results are similar when only the low end of language ability is studied, with the possible exception of the two receptive measures," she said. "This similarity is consistent with the hypothesis that the same genetic and environmental influences are involved in shaping individual differences and differences in risk of a language-related disorder. If this turns out to be the case, it means that when genes and specific aspects of environments that affect language disability are discovered, they will be also involved in individual differences in language ability."
Study results also suggest that the same genes and environments similarly affect individual differences in the language ability of boys and girls.
"Establishing the role of genetic influences in diverse aspects of language is only a first step in providing a foundation and a motivation for molecular genetic studies to find the multiple specific genes involved," said Kovas. "Similarly, establishing the relative importance of environmental influences is just a first step toward future research to identify specific environments involved. As specific genes and environments are identified, we can begin to understand the complex mechanisms of development of individual differences in language abilities."