A sign is something that refers to something else. Signs, whether of natural or cultural origin, act by provoking a receptive system, human or nonhuman, to form an interpretant (a movement or a brain activity) that somehow relates the system to this “something else.” Semiotics sees meaning as connected to the formation of interpretants. In a biosemiotic understanding living systems are basically engaged in semiotic interactions, that is, interpretative processes, and organic evolution exhibits an inherent tendency toward an increase in semiotic freedom. Mammals generally are equipped with more semiotic freedom than are their reptilian ancestor species, and fishes are more semiotically sophisticated than are invertebrates. The evolutionary trend toward the production of life forms with an increasing interpretative capacity or semiotic freedom implies that the production of meaning has become an essential survival parameter in later stages of evolution.