Published online by Cambridge University Press: 05 November 2012
Through the last two chapters, we have built up a picture of the physical and neurological systems underpinning language in modern humans. We have tried wherever possible to make suggestions about the stages in the human family tree where innovations in vocal tract structure or brain size and conformation may have arisen; and perhaps even more importantly, we have introduced all the multifarious reasons why fossil evidence does not lend itself to absolute or conclusive interpretation. The biological comparative method does allow these human systems to be compared with those in other living species, and reveals both continuities and discontinuities; this helps us begin to catalogue those aspects of human anatomy and brain structure and function which may be special, and may be linked with language. Investigations of modern humans, both those with specific deficits and, increasingly, given the advent of new and less-invasive technologies, those functioning normally, can tell us more about how the brain contributes to language learning, production and perception.
However, we agreed at the outset that we would consider behaviours like language as reflexes of structures like the brain and the vocal tract; and in turn, that those structures must be seen in an evolutionary context, as the outcomes of inheritable modifications in the genetic code. Understanding the structures, therefore, crucially means understanding the forces that modify genes in populations, and the mechanisms by which those genes interact with the environment to build individuals. In the two main sections of this chapter, after introducing some central ideas and concepts from genetics, we will therefore turn to the techniques of modern population genetics and molecular genetics respectively. For population genetics, we shall concentrate on the dynamics of gene frequencies over time, developing in more detail processes like mutation, natural selection and drift which were introduced briefly in Chapters 1 and 2 above. If we understand these forces, we may be able to reverse them to reconstruct the timescale for certain changes among populations, even where direct evidence is not available. Turning to molecular genetics, we shall consider how genes influence the construction of particular systems both during embryological development and later, in association with learning. As ever, we shall find that understanding how systems work normally mainly follows from observing and explaining cases where they go wrong.