Ed Yong

There are fewer than 100 species of bacteria that cause infectious diseases in humans

Islands are where you go if you want to find life at its most outlandish, gaudy, and superlative. Their isolation, restricted boundaries, and constrained size allow evolution to go to town. The patterns of biology resolve into sharper focus more readily than they would do on the extensive, contiguous mainland.

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 somemicrobe – just not always the same one

Every organ is also variable in itself. The microbes that live at the start of the small intestine are very different from those in the rectum. Those in dental plaque vary above and below the gum-line. On the skin, microbes in the oily lakes of the face and chest differ from those in the hot and humid jungles of the groin and armpit, or those colonising the dry deserts of the forearms and palms. Speaking of palms, your right hand shares just a sixth of its microbial species with your left hand

Microbes have opened many doors for animals, allowing them to take up all kinds of peculiar lifestyles that would normally be closed off to them. And when animals share habits, their microbiomes often converge. For example, Knight and his colleagues once showed that ant-eating mammals, including pangolins, armadillos, anteaters, aardvarks, and aardwolves (a type of hyena), all have similar gut microbes, even though they have been evolving independently for around 100 million years