One of the central issues in cognition today is
the degree to which cognitive abilities such as language are the
result of specialized, genetically-encoded structures and
predispositions (e.g., Pinker, 1994, Stromswold, 2000). In order to
determine the extent to which genetic and environmental factors play
a role in normal language and language disorders, we have conducted
comprehensive reviews and meta-analyses of over 80 existing family
aggregation studies, pedigree studies, sex-ratio studies, linkage
studies, quantitative trait loci studies, twin studies and adoption
studies which investigate the heritability of language. These
meta-analyses reveal that heritable factors play a strong role in SLI
and dyslexia, and in normal spoken and written language (Stromswold, 1996a,
1998, 2001, 2005a). These analyses also suggest some of these
heritable factors are specific to linguistic tasks.
We have also collected and
analyzed longitudinal data from of a set of monozygotic (MZ) and
dizygotic (DZ) SLI twins (Stromswold & Rifkin, 1996). Even
though all 4 children were diagnosed as being SLI, for all measures
(age of acquisition, rate of errors, indices such as mean length of
utterance and type/token ratios, performance on comprehension and
production tests, etc.) and all areas of language assessed
(phonology, lexicon, morphology, and syntax), the MZ twins were more
similar to one another than the DZ twins. Furthermore,
consistent with recent findings of Robert Plomin and Steven Reznick,
whereas the MZ twins continued to exhibit very similar linguistic
profiles over the course of the study, the DZ twins became
linguistically more different as time passed. These results
indicate that genetic factors play an important role in the
acquisition of all aspects of language and that the role of genetic
factors may increase as children get older.
In our on-going
Perinatal Environment and Genetic Interactions (PEGI) twin study (Stromswold 2005a, 2005b, 2006a, 2006b, 2007; Stromswold et al., 2005), we are investigating how perinatal environment and genetic factors acting along and in concert with other factors affect linguistic and nonlinguistic development. Initial results of this study indicate that 1) genetic factors play a greater role in the linguistic abilities of language-impaired than those of normal twins; 2) genetic factors play a role in all aspects of language, 3) some of these factors are specific-to-language and some are not, 3) some genetic factors are specific to particular aspects of language (e.g., genetic factors that affect articulation and syntax but not vocabulary/lexical access), 4) genetic factors play a greater role for articulation and syntax than for vocabulary/lexical access), 5) adverse perinatal factors affect linguistic development more than cognitive development, and 6) adverse postnatal factors (e.g., low SES) affects cognitive development more than linguistic development.
Lastly, we have explored the relationship between genetics and the structure, acquisition and evolution of language (Ganger & Stromswold, 1998; Stromswold, 2005b, 2007).
Relevant Papers
Stromswold, K. 1996a. The genetic basis of language acquisition. Proceedings of the 20th Annual Boston University Conference on Language Development 2 , 736-747
Stromswold, K. 1996b. Genes, specificity and the lexical/functional distinction in language acquisition. Behavioral and Brain Sciences 19, 648-9
Stromswold, K. 1998. Genetics of spoken language disorders Human Biology, 70 , 297-324.
Last updated February 2007.