““When microbiologists first started cataloguing the human microbiome in its entirety they hoped to discover a "core" microbiome: a group of species that everyone shares. It's now debatable if that core exists. Some species are common, but none is everywhere. If there is a core, it exists at the level of functions, not organisms. There are certain jobs, like digesting a certain nutrient or carrying out a specific metabolic trick, that are always filled by some microbe-just not always the same one. You see the same trend on a bigger scale. In New Zealand, kiwis root through leaf litter in search of worms, doing what a badger might do in England. Tigers and clouded leopards stalk the forests of Sumatra but in cat-free Madagascar that same niche is filled by a giant killer mongoose called the fossa; meanwhile, in Komodo, a huge lizard claims the top predator role. Different islands, different species, same jobs. The islands in question could be huge land masses, or individual people.””
