Time and again, microbes have opened doors for animals, allowing them to exploit niches that would have otherwise been denied to them by their basic animal-ness. By providing nutrients that are missing from the sap of plants, bacteria have allowed bugs to subsist on a diet of nothing else, turning them into the bane of greenery and greenhouses worldwide. By breaking down the tough and typically indigestible carbohydrates in plant matter, bacteria allowed mammals to become extreme grazers and gave rise to the thundering herds of Africa’s plains. By providing a source of energy that isn’t tied to sunlight, bacteria allowed worms, clams, and hundreds of other creatures to colonise the abyssal oceans, and lose their mouths and guts in