  Next, Hauser et al. speculate that the only thing that's really  special about the human FLB is the FLN. That is, with the exception  only of the FLN, FLB comprises systems that are shared with (or only  slight modifications of) systems in other animals. Consequently,  there is no mystery (or no more mystery than usual) about how these  language-related abilities evolved. FLN, on the other hand, is  distinctive to humans and what is special about it is its power of  recursion, that is, its ability to categorize linguistic  objects into hierarchically organized classes, and (on the behavioral side) for the generation of infinitely many sentences out of finitely many words. According to Hauser et al., the only real evolutionary  mystery about language is how this capacity for recursion evolved  — and this question, argue Hauser et al, is eminently  addressable by normal biological methods (e.g., comparative studies  to determine possible precursor mechanisms, etc.).