Based on the motor theory of language, which asserts an evolution from gestures along several stages to today's speech and language, we suggest that speech ontogeny may partly reflect speech phylogeny, in that perception of prosodic contours is an intermediary stage between a manual communication system and a fully developed language faculty.
We add evidence in support of Corballis's gestural theory of language. Using transcranial magnetic stimulation, we found that productive and receptive linguistic tasks excite the motor cortices for both hands. This indicates that the language and the hand motor systems are still tightly linked in modern man. The bilaterality of the effect, however, implies that lateralisation is a secondary issue.