The differences between voices are often broadly categorized as either 'organic' or 'learned', implying that some are determined by our anatomical inheritance, and others by what we copy from people around us or choose in order to mark our individuality. It is normally impossible, however, to assign observable differences to one source or the other, since neither source is experimentally controllable. In the case of identical twins, nature provides such a control. It can reasonably be assumed that the anatomical differences within a pair of identical twins are minimal. Differences between their voices, if any, may be attributed to 'learning' and, furthermore, if the twins have grown up in the same environment, to choices rather than to direct imitation. This paper presents a study of the /l/ and /r/ phonemes of three pairs of identical twins.