In addition, a message that carries “semantic information”, it is often thought, has the capacity to mis-represent, as well as accurately represent, what it is about. There is a capacity for error. Shannon information does not have that feature; we cannot say that one variable “carried false information” about another, if we are using Shannon’s sense of the term. But biologists do apparently want to use language of that kind when talking about genes. Genes carry a message that is supposed to be expressed, whether or not it actually is expressed. Thus the developmental disorders caused by thalidomide in the 1960s were due to an inability to use genetic signals that were supposed to control limb development. These genes were present and active; thalidomide did not do its harm by causing mutations.