Approximately 3.5 billion years ago, conditions were just right on Earth for life to begin, as phospholipids formed spheres around self-replicating nucleic acid chains. I mean, probably. I wasn’t there. But that’s one of the better explanations we have right now. These life forms would have been the earliest bacteria and archea — prokaryotic cells with no distinct nucleus. The first way these cells figured out how to cooperate was in the form of biofilms. This matrix of polysaccharides, proteins, and nucleic acids provide the cells a surface to stick to and protection from the elements. Once they were in a set colony, the cells figured out that they didn’t all have to do all the work all the time: some could specialize to do certain tasks. Eventually, the cells would become so specialized that they wouldn’t be able to live on their own anymore, making the colony a multi-cellular organism. Some cells provided protection (early shells), while others would absorb nutrients (early gastrointestinal tracts), and other lazy jackasses would mooch off others’ work while telling them what to do (middle management… I mean, neurons).

It’s easy to think that in the next couple of billion years, we left our single cell ancestors behind, only interacting with them as enemies trying to infect us. Single-celled organisms are still with us, though, and not just a couple of them. As of the latest count, 43% of the cells that compose the human body aren’t human—instead, nearly half of us is made up of bacteria, viruses, fungi, and archea. These aren’t freeloaders either; in fact, we couldn’t live without them. They help us digest food, prevent infection from parasitic organisms, and maintain the health of our GI tract, skin, and vaginas (no, that’s not a dirty word).

Recent studies have demonstrated that the gut microbiome in particular is integral to our overall health. National Institutes of Health research has found connections between the microbiome and circadian rhythms, inflammatory bowel disease, Crohn’s Disease, and neonatal sepsis. And while causation is not certain, the increased use of antibiotics certainly disrupts the microflora and has correlated with increases in obesity, asthma, allergies, and diabetes.

The other main disruption to the microbiome in the last several decades is the rise in caesarian section births. The first inoculation of our gut with bacteria comes from the vaginal wall—when babies are removed surgically, they never get that initial colony of lactobacillus, and instead are colonized by skin bacteria from the first hands to touch them. It has since become standard procedure to inoculate the new baby with a vaginal swab when born via C-section.

With all this information, it’s tempting to want to eat as many probiotics as possible. The principle is very sound—a fresh gut colony from fecal transplants is the absolute best cure for a Clostridium difficile infection, for instance. However, commercially available products have not been shown to affect the gut bacteria. What you can do is eat more fiber-rich whole grains and vegetables (which bacteria love) and less fat and sugar (which bacteria hate) to provide them as comfortable an environment as possible.

That’s not what you wanted to hear at all, was it?

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