“From March to October in our imaginary calendar, they [bacteria] had the sole run of the planet. During that time, they changed it irrevocably. Bacteria enrich soils and break down pollutants. They drive planetary cycles of carbon, nitrogen, sulphur and phosphorus, by converting these elements into compounds that can be used by animals and plants and then returning them to the world by decomposing organic bodies. They were the first organisms to make their own food, by harnessing the sun’s energy in a process called photosynthesis. They released oxygen as a waste product, pumping out so much of the gas that they permanently changed the atmosphere of our planet. It is thanks to them that we live in an oxygenated world. Even now, the photosynthetic bacteria in the oceans produce the oxygen in half the breaths you take, and they lock away an equal amount of carbon dioxide.” 

Bacteria have been around for much longer than we have and have shaped our planet as we know it. This quote summarizes the impact they have had on preparing the planet for multicellular species.

“Each of us has our own distinctive microbiome, sculpted by the genes we inherited, the places we’ve lived in, the drugs we’ve taken, the food we’ve eaten, the years we’ve lived, the hands we’ve shaken.” 

Our microbiome is unique and shaped by the world around us. These facts account for why evolution can act on not just us but our bacteria. We are constantly shaping our microbiome with our everyday actions.

“‘The history of warfare always looks more glamorous than accounts of co-operation.’” 

The French scientist Rene Dubos said these words. Yong uses this quote in discussing how much of the history of microbial research was conducted to figure out how to kill microbes, and Dubos was one of few at that time not to view microbes as enemies. This viewpoint was critical in shifting research from killing microbes to learning about them.