Talking Genes

To the Editors:

It is of course gratifying to find my work on inherited language impairment repeatedly cited by such distinguished scholars as Philip Lieberman and Noam Chomsky, as has happened in a recent and extended exchange in your columns [NYR, Letters, October 10 and December 19, 1991]. They clearly appreciate that this inherited disorder is important because it allows us to investigate the innateness of language in new ways. I am bemused, however—as I am sure any of your readers who have followed this exchange must also be—to see my findings used to support all sides of the argument. It is important, therefore, for me to make clear the significance of my research.

Zuckerman, responding to Chomsky, raises as an ongoing question an issue that I believe can be clearly settled by looking at inherited language impairment over several generations. In The New York Review he claims that whether “man’s syntactical abilities [are] due to one set of interacting genes or more than one [is] anyone’s guess.” While this question may have been “anyone’s guess” in the past, there is now converging evidence from several studies that provide a clear answer: though certain cases of developmental language impairment are associated with a single autosomally dominant gene, these impairments affect only part of language—the ability to construct general agreement rules for such grammatical features as tense and singular/plural—and leave all other aspects of language, such as word order and the acquisition of lexical items, unaffected. These facts answer Zuckerman’s question: Language must be the result of several sets of interacting genes that code for different aspects of language rather than a single set of interacting genes. In fact it is misleading to think of “language” or “grammar” as unitary phenomena. Inherited language impairment shows that different parts of grammar are controlled by different underlying genes.

Lieberman cites my work to support the argument that there is genetic variability in language. In fact, my work shows that there are two different genotypes, one which results in the normal development of morphological rules in language and another that results in an inability to learn this specific aspect of language in the normal way. This means, obviously, that language involves different genotypes; but variability across genotypes is quite a different issue than variability within a genotype. Language impaired subjects are not merely less good at certain aspects of language than normals—the way they learn these aspects of language is profoundly different than the way the rest of us do. The kind of variability within normal language users that Lieberman is searching for cannot really be extrapolated from the populations I have studied.

Chomsky is sanguine that my results can be welcomed because they are “interesting evidence for what had been assumed.” In fact, while this work does support his basic hypothesis that some aspects of language are innate, it raises serious questions about precisely which aspects of language they are. For example, it can be shown that a wide range of phenomena, from noun-verb agreement to the sequence of tenses in narratives, are impaired in similar ways. Though these properties are all “agreement relationships” in some sense, there is no present theory of grammar, including Chomsky’s, in which they are treated in the same way.

The arguments about innateness have been based on inferences from theoretical models of language. We now have a natural experiment that provides an entirely new source of information. These new facts do not merely confirm what has been assumed, but rather force us to revise widely held assumptions about the fundamental structure of language.

M. Gopnik
Department of Linguistics
McGill University
Montreal, Canada

Lord Zuckerman replies:

While I have a general interest in the subject, I must again point out that I am not a professional scholar of linguistics, and therefore have to leave it to Lieberman and Chomsky to reply as they think fit to Professor Gopnik’s letter, and to Lieberman to sort out whatever differences he has with Chomsky. These do not affect either what I said in my review (in the May 30, 1991, issue) or in my subsequent letters. Equally, since I am not a professional geneticist, I can do no more than express my interest in Professor Gopnik’s view that her work provides part of an answer to my observation that it is anybody’s guess whether “man’s syntactical abilities are due to one set of interacting genes or more than one.” As I understand it, she has concluded that a dominant autosomal gene, with presumably a precise locus on a particular chromosome, is responsible for one set of the features that characterize the syntactic aspects of language. If her conclusion is confirmed by the further studies to which she refers, presumably the same gene will be shown to be responsible for corresponding defects in the speech of children, whose native language does not have the same syntactic rules as apply to English—the language of the three generations of the family that she has studied. It would be particularly interesting if these further studies could take in samples of monozygotic twins who are brought up separately in different social environments.