The Ancestor's Tale: A Pilgrimage to the Dawn of Evolution

by Richard Dawkins

A family codenamed KE suffers from a strange hereditary defect. Out of approximately 30 family members spread over three generations, about half are normal, but 15 show a curious linguistic disorder, which seems to affect both speech and understanding. It has been called verbal dyspraxia, and it first shows itself as an inability to articulate clearly in childhood. Some authorities think the problem largely stems from co-ordinating rapid movements of the face and mouth. Others suspect the problem lies deeper, since it affects comprehension and written language too. What is clear is that the abnormality is genetic. Individuals either have it or they don’t, and it is associated with a mutation of a gene, present in all vertebrates, called FOXP2. This gene encodes a ‘transcription factor’: a protein which binds onto other DNA and switches on and off other important genes, in this case in various parts of the brain. The particular mutation in the KE family disrupts this binding. It is fortunate that the affected individuals have a second, normal copy of FOXP2 inherited from their other parent. Fortunate, because experiments have shown that mice which have two similarly mutant copies die very young, probably as a result of brain, lung and movement defects. This clearly shows that FOXP2 is not simply a ‘gene for language’, as it is sometimes touted in the press. Nevertheless, the evidence of the KE family suggests that in humans FOXP2 is important for the development of some par...