Telos is in vogue in biosemiotic researches, which present the teleological solution as anti-Darwinian, while it is more often, for biologists, only ante-Darwinian. The assimilation of structuring contents to a “function”, and of the function to a “goal”, in an irreversible temporality, is the most frequent basis of this methodological creepage. The teleology is based on a projective and ascending epistemic orientation, to which we can oppose a retrojective, descending and achronic one, including modal and sensitive interactional semiotics. For semiotics, the challenge lies in the nature of its relationships with other disciplines, particularly biology. Indeed, we see that the temptation is great for semioticians to dwell precisely in the shadows and shams of other disciplines, and to call “sign” or “semiosis” what other sciences seem to have still some trouble to explain, with the risk of only confronting problems that will soon be obsolete. We propose here the theoretical and methodological principles of structural biosemiotics, and precisely attentive to the problems that biologists face, solve and renew.