Language Evolution: Enlarging the Picture

Contemporary biology understands macro-evolutionary steps as changes in developmental processes: the timing and placement of the expression of genes and their interactions through the environment. This is evo-devo — evolutionary developmental biology. Genes are organised in partially modular control cascades, so a change in a gene far up in a cascade can alter the timing and/or placement of whole complex modular processes, and thus the environment of operation of many other genes, and therefore large-scale coordinated phenotypic features. The classic example is the repeated process that puts pairs of legs on each of an insect’s segments, which can, at a single mutation, go on for an extra segment, placing a pair of legs on the insect’s head. A large number of genes coordinate to produce a pair of legs, but a single element can control when and where this genetic module is expressed.1 An excellent introduction to evo-devo for the non-biologist is Carroll (2005).