Honouring our microbial ancestors

The bacteria that now pose the greatest threats to humans are products of our own making. The evolution of pests and pathogens resistant to human poisons has a long, well-documented history. Hospitals, where antibacterial drugs, soaps, and cleaners are used in volume, are hotbeds of antibiotic-resistant strains of bacteria. Farmers feed livestock excessive amounts of antibiotics, thereby selecting for bacteria that are resistant to those medicines-versions of which are also used for humans.

But our xenophobia also blinds us to a more fundamental insight: the health of our environment, and our bodies, depends on bacterial communities. Indeed, they are responsible, as ancestors, for our very existence.

If Life had a yearbook, bacteria would win all of the awards, especially "most likely to succeed." A bacterium is an organism made up of one or more small prokaryotic cells, those that have DNA genes but lack nuclei and chromosomes. Bacteria inhabit the farthest reaches of the biosphere. They live in the hottest, coldest, deepest, saltiest, and most acidic environments. They are the most ancient lifeform, having lived on Earth for at least 3.8 billion years, over 80 percent of its history. By contrast, humans have occupied a narrow range of environmental conditions-and for only about 0.003 percent of the Earth's existence. If we even made it into the yearbook, the caption would have read "photo not available."