Prodi explains semiosic phenomena by means of the model of the circle. This model allows to account for a very important feature of the natural world: in life phenomena, there is no a one-way causal arrow, from the lenvironment to the living organism and vice versa. According to Prodi in the lifeworld, there is a two-way relation between cause and effect; the genotype causes the phenotype, but the latter in turn modifies the evolutionary environment, thus ultimately applying an indirect causal pressure back on the genome itself. In this way, it is possible to account for the dynamism of the world of life. The biological world, the world of semiosis, is not closed off, but it continuously expands and develops. The circle of life is best conceived as a spiral. The transition from the circle to the spiral is necessary in order to account—in a biological register—in particular for the evolution and the mutation of human language and culture.