A simple example of a holobiont is a coral. Scientists have long known that corals are a union of two species: polyps that create the calcium carbonate “skeleton” and algae that create nutrients through photosynthesis. But where they once saw a duet, there is a growing realization that corals are really a whole choir of endolithic algae, polyps, prokaryotes, fungi, plastids, and viruses, all interdependent on each other.
You are not really “you”
What is true for plants and corals is also true for animals. It is no longer possible to think of animals as distinct from the microbial communities they share a body with. A cow cannot digest grass, but the microbes that live in its stomach can. Cows’ bodies have evolved to house the microbes that sustain them. Similarly, the human gut contains about 1,000 major bacterial groups which together are called the “microbiome.”