A tiny Hawaiian squid, Euprymna scolopes, has become a model for thinking about this process. The “bob-tailed squid” is known for its light organ, through which it mimics moonlight, hiding its shadow from predators. But juvenile squid do not develop this organ unless they come into contact with one particular species of bacteria, Vibrio fischeri. The squid are not born with these bacteria; they must encounter them in the seawater. Without them, the light organ never develops. But perhaps you think light organs are superfluous. Consider the parasitic wasp Asobara tabida. Females are completely unable to produce eggs without bacteria of the genus Wolbachia. Meanwhile, larvae of the Large Blue butterfly Maculinea arion are unable to survive without being taken in by an ant colony. Even we proudly independent humans are unable to digest our food without helpful bacteria, first gained as we slide out of the birth canal. Ninety percent of the cells in a human body are bacteria. We can’t do without them.
As biologist Scott Gilbert and his colleagues write, “Almost all development may be codevelopment. By codevelopment we refer to the ability of the cells of one species to assist the normal construction of the body of another species.” This insight changes the unit of evolution. Some biologists have begun to speak of the “hologenome theory of evolution,” referring to the complex of organisms and their symbionts as an evolutionary unit: the “holobiont.” They find, for example, that associations between particular bacteria and fruit flies influence fruit fly mating choice, thus shaping the road to the development of a new species. To add the importance of development, Gilbert and his colleagues use the term “symbiopoiesis,” the codevelopment of the holobiont. The term contrasts their findings with an earlier focus on life as internally self-organizing systems, self-formed through “autopoiesis.” “More and more,” they write, “symbiosis appears to be the ‘rule,’ not the exception. . . . Nature may be selecting ‘relationships’ rather than individuals or genomes.”
Anna Lowenhaupt Tsing, The Mushroom at the End of the World: On the Possibility of Life in Capitalist Ruins














