Purpose Since proposed by Darwin, evolution is considered to be dependent on a source of genetic variability that must be constrained by environmental conditions in order to generate stable (adapted) phenotypes. Several sources and causes of this variability have been proposed so far. This paper aims to posit that ambiguity of fuzzy grammars is the main source of genetic variability on which natural selection operates. Design/methodology/approach Formal grammars (FG) were proposed as the tool to deal with human and artificial languages. Fuzzy formal grammars (FFGs) are the extension of the formalism in the Theory of Fuzzy Logic and are ambiguous grammars. Here, the ambiguity of the ordered set of chemical interactions – the so‐called signal transduction pathways (stp), linking membranes events to DNA reading and protein synthesis – is assumed as an inner source of variability that must be constrained by environmental conditions. Fuzzy formal languages (FFL) theory is used to mathematically formalize the biology concept of stp. Findings The genome variability is the result of the constraints imposed by the environment on the grammar intrinsic ambiguity. Practical implications The formalism of this model provides a new way to analyze and interpret the findings of the different genome sequencing projects. Originality/value The theoretical framework developed here provides a new perspective of understanding the code of life and evolution.