I recently learned that sign language is not international. British sign language is different from German sign language, for example. How did this arise, when it would appear to be an area where language barriers could have been broken down? And are there interpreters from one sign language into another?

Mike Crabtree, Dusseldorf Germany

• Contrary to popular belief, sign language is not dependent solely on the use of hand and body gestures. People speaking will mouth words and those words, in conjunction with hand gestures will specify exact meaning and, importantly, syntax (which is different for different spoken languages). A universal sign language would be very difficult to achieve, if not impossible. When we talk about British Sign Language we are really talking about a means of communication for the use of non-hearing British English speakers.

  Max Wurr, Stanmore UK

• The reason that most sign languages are mutually incomprehensible lies in their origins. A few centuries ago, deaf and mute children were unlikely to be in contact with other children with the same disability. Forced to communicate with users of oral languages, they individually devised gestures to communicate their needs. These were simple and probably fairly universal (of the type used by those travelling abroad, such as pointing to the mouth to mean "food"). However, when the deaf were put in institutions, they had to opportunity to develop complex systematic languages to fulfil their "language instinct". With no chance to use oral language, instead "language spilled from their fingertips" (Pinker). Evidence from deaf children and those in other unusual linguistic environments such as pidgin/creole speaking areas seems to suggest there is some form of innate device in the brain which systematically develops "language" through whatever means possible. Given no comprehensible or sufficient outside stimulus, children will develop strikingly similar languages (in terms of the grammatical basis, such as word order, development of tense, negation, mood and aspect etc). The best example of this may be the Nicaraguan deaf children who were compulsarily institutionalised and who quickly developed their own Nicaraguan Sign Language. In each country with a sizeable deaf community and the means to concentrate deaf children in one area, a sign language has arisen - the gestures themselves vary across languages of course. Interestingly, while British and American Sign Languages are not intelligible between one another, French and American are, as the US version is based on the earlier French language. There are even accents in Sign Languages: Chinese speakers keep the thumb tucked in the palm for most signs, whereas Americans do not - this applies even when Chinese users are signing in American! There are skilled translators for most of the world's major Sign Languages, although obviously far fewer than the number of 'normal' language users who can translate into Sign.

  Jon, Cambridge