Heritability in syntactic development: a critique of Munsinger and Douglass.

Munsinger and Douglass (Child Development, 1976, 47, 40-50) used the Assessment of Children's Language Comprehension and the Northwestern Syntax Screening Test as measures of syntactic ability to investigate the heritability factor in language acquisition. By comparing the concordance of scores of twins and siblings, they concluded that heritability was the important variable in test performance (h2 = .79) and that environmental influences were not much over, 10. In the present critique, weaknesses regarding test measures are pointed out, and the validity of these measures for the ages of the children used in the study is questioned. It is also emphasized that the question of environmental effects in normal circumstances remains unquantified, and research indicates that language intervention programs with deficient populations can be beneficial.