Mammalian and insect STING detect both 2′3′- and 3′3′-CDNs but appear to favor 2′3′-cGAMP as a ligand9,62, and the cGAS enzyme from the sea anemone produces 2’3’-cGAMP14, raising the possibility that the 2′–5′ linkage was co-opted in metazoans to increase the signal-to-noise ratio in the context of viral infections in multicellular organisms tightly associated with a microbial flora. This evidence concerns the gene CGAS and viral infectious disease.