Other Minds: The Octopus, the Sea, and the Deep Origins of Consciousness

by Peter Godfrey-Smith

Bacteria living inside a Hawaiian squid produce light by a chemical reaction, but only if enough other bacteria are around to join in. The bacteria control their illumination by detecting the local concentration of an “inducer” molecule, which is made by the bacteria and gives each individual a sense of how many potential light producers are around. As well as lighting up, the bacteria follow the rule that the more of this chemical you sense, the more you make. When enough light is being produced, the squid who house the bacteria gain the benefit of camouflage. This is because they hunt at night, when moonlight would normally cast their body’s shadow down to predators below. Their internal lights cancel the shadow. Meanwhile, the bacteria seem to benefit from the hospitable living quarters provided by the squid.