IMAGINE a scientist gently swabs your left nostril with a Q-tip and finds that your nose contains hundreds of species of bacteria. That in itself is no surprise; each of us is home to some 100 trillion microbes. But then she makes an interesting discovery: in your nose is a previously unknown species that produces a powerful new antibiotic. Her university licenses it to a pharmaceutical company; it hits the market and earns hundreds of millions of dollars. Do you deserve a cut of the profits?

It is a tricky question, because it defies our traditional notions of property and justice. You were not born with the germ in your nose; at some point in your life, it infected you. On the other hand, that microbe may be able to grow and reproduce only in a human nose. You provided it with an essential shelter. And its antibiotics may help keep you healthy, by killing disease-causing germs that attempt to invade your nose.

Welcome to the confusing new frontier of ethics: our inner ecosystem. In recent years, scientists have discovered remarkable complexity and power in the microbes that live inside us. We depend on this so-called microbiome for our well-being: it helps break down our food, synthesize vitamins and shield against disease-causing germs.

“We used to think of ourselves as separate from nature,” said Rosamond Rhodes, a bioethicist at Mount Sinai School of Medicine. “Now it’s not just us. It’s us and them.”