Applying a semiotic perspective to nature, one is immediately struck by the fact, that living systems exhibit what might be termed code-duality. The DNA may be seen as a digital-code version of the organism, while the population may be seen as an analog-coded version of the species' gene pool – or, as I prefer to call it, "the language of the species". (Thus, to follow Saussure, the DNA of the single organism may be seen as "parole", whereas the deep structure hidden in the total genetic message of the species could be seen as "langue" [...,] Saussure 1916). This code-duality seems, in fact, to be the most remarkable thing which sets living systems apart from inanimate nature.
Hoffmeyer, J. (1987). The constraints of nature on free will. In: Mortensen, V. & Sorensen, R.C. (eds.). Free Will and Determinism, 188-200: 193.
the central feature of living systems allowing for self-reference, and thus the ability to select and respond to differences in their surroundings, is code-duality, i.e. the ability of a system to represent itsel in two different codes, one digital and one analog (Hoffmeyer 1987).
Hoffmeyer, J. & Emmeche, C. (1991). Code-duality and the semiotics of nature. In: Anderson, M. & Merrell, F. (eds.). On Semiotic Modeling, 117-166: 126.