Genes, proteins and domain-specificity
Authors: Gary F. Marcus
Journal: Trends in Cognitive Sciences (1999)

In their response to van der Lely et al.1van der Lely H. Rosen S. McClelland A. Evidence for a grammar-specific deficit in children.Curr. Biol. 1998; 8: 1253-1258Abstract Full Text Full Text PDF PubMed Scopus (119) Google Scholar, Tomblin and Pandich appear to doubt the possibility that ‘specific aspects of language content’ are ‘under specific genetic influence’ on the grounds that ‘the only thing genes do is code for proteins or control the expression of other genes that code for proteins. As proteins are highly conserved in nature, it would seem unlikely that there could even be one new protein in biology that has a special role for language let alone the number that would probably be necessary for influencing language’2Tomblin J.B. Pandich J. Lessons from children with specific language impairment.Trends Cognit. Sci. 1999; 3: 283-285Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar. The implicit premise seems to be that language could be under specific genetic influence only if humans possessed a number of proteins that cannot be found elsewhere in the animal kingdom. Tomblin and Pandich could well be correct that there are no human-specific proteins, but this would not lead us to infer that humans could not possibly have language. The implicit premise that novel structure depends on novel proteins is demonstrably false. For example, old proteins can be adapted for new uses. The lens of all vertebrate eyes is made up in large part of a class of proteins known as crystallins, which contribute to the ability of the lens to focus. Some of these crystallins probably originally existed for the purpose of protection from heat, and only later did they become involved in the bending of tissue that contributes to focusing; the new function of focusing thus might have depended not on the existence of a new protein, but on a set of mechanisms that co-opted an old set of proteins to new uses3Gerhart J. Kirschner M. Cells, Embryos, and Evolution. Blackwell Science, 1997Google Scholar. By acting as switches, specific ‘master control genes’ can trigger complex, hierarchical cascades of genes that elicit widely varying arrangements of cells, even in the absence of species-particular proteins4Gehring W.J. Master Control Genes in Development and Evolution: The Homeobox Story. Yale University Press, 1998Google Scholar. Van der Lely et al.’s view that aspects of language may be under specific genetic control thus remains viable. It could turn out, for instance, that the language impairments that van der Lely et al. observed reflect the absence of some particular gene that ordinarily triggers a cascade of events that leads to the construction of machinery that uniquely subserves language. As Tooby and Cosmides put it, ‘There are millions of animal species on earth, each with a different set of cognitive programs. The same basic neural tissue embodies all of these programs, and it could support many others as well. Facts about the properties of neurons, neurotransmitters, and cellular development cannot tell you which of these millions of programs the human mind contains. Even if all neural activity is the expression of a uniform process at the cellular level, it is the arrangement of neurons – into bird song templates or web-spinning programs – that matters’5Cosmides L. Tooby J. Beyond intuition and instinct blindness: toward an evolutionary rigorous cognitive science.Cognition. 1994; 50: 41-77Crossref PubMed Scopus (283) Google Scholar.