To what is a baby predisposed?

Here's a little tidbit for you to contemplate. Laura Ann Petitto and colleagues have studied language acquisition by children exposed to both spoken and signed language inputs (Petitto, Laura Ann, “On the biological foundations of human language,” in Emmorey et al, Eds., The Signs of Language Revisited, Lawrence Erlbaum, 2000). While some theories have posited that the human animal is predisposed toward spoken language by its neurological and physiological structure, it has never been clear what these theorists consider language to be. The first matter of defining our subject has too often simply been skirted. It has been tacitly assumed that language means speech. From this, many theories have been hatched explaining some of the changes to human physiology in terms of their selection for speech.

For example, Philip Lieberman (Lieberman, Uniquely Human: The Evolution of Speech, Thought, and Selfless Behavior, Cambridge, MA Harvard University Press, 1991.) has long argued that bipedalism in humans was the result of selective pressures for a descended larynx which permits non-nasalized vocalizations. The argument is that speech is such an advantage that it counters the detriments caused by a descended larynx, in particular the likelihood of choking.

The argument has always been based on the assumption that the two (choking and speech) are the relevant countering forces, driving the evolution of bipedalism. Let's step back from this for a minute and take a closer look at language.

Petitto and her colleagues indicate that many of the same neural substrates are shared for both speech and sign, even for specific brain regions (in particular the Planum Temporale that had been thought exclusively to play a role in auditory processing). To put it simply, parts of the brain that were previously seen as part of hearing, are exposed to play a role for soundless language.

As she writes (p. 470):

Rather that being exclusively hard-wired for speechor sound, the young of our species are initially hardwired to detect aspects of the patterning of language.

The point to be taken from this is that our assumptions regarding language have been flawed. Human language, and for that matter much of human culture, is characterized by patterns, whether in sound or movement, or what have you. It is the task of infants to identify and make sense of these patterns. The more the patterns are identifiable and repeatable, the easier their task becomes.