A Note on Zipf's Law, Natural Languages, and Noncoding DNA regions

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 t 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 nite-state branching process. to analyzing linguistic texts to the statistical study of DNA base pair sequences and nd that the noncoding regions are more similar to natural languages than the coding sequences" (p. 3169). Speciically, the authors analyze coding/noncoding DNA sequences and conclude that noncoding regions show a more Zipf-like behavior than coding regions. Asserting that \A remarkable feature of languages is Zipf's law" (p. 3169), they further conclude that noncoding regions are more similar to natural languages than coding regions (p. 3170): 1