  In Phys. Rev. Letters (73:2, 5 Dec. 94), Mantegna et al. conclude on the
basis of Zipf rank frequency data that noncoding DNA sequence regions are more
like natural languages than coding regions. We argue on the contrary that an
empirical fit to Zipf's ``law'' cannot be used as a criterion for similarity to
natural languages. Although DNA is a presumably an ``organized system of
signs'' in Mandelbrot's (1961) sense, an observation of statistical features of
the sort presented in the Mantegna et al. paper does not shed light on the
similarity between DNA's ``grammar'' and natural language grammars, just as the
observation of exact Zipf-like behavior cannot distinguish between the
underlying processes of tossing an $M$ sided die or a finite-state branching
process.
