I Contain Multitudes: The Microbes Within Us and a Grander View of Life

by Ed Yong

In fact, every individual is more like an archipelago – a chain of islands. Each of our body parts has its own microbial fauna, just as the various Galapagos islands have their own special tortoises and finches. The human skin microbiome is the domain of Propionibacterium, Corynebacterium, and Staphylococcus, while Bacteroides lords over the gut, Lactobacillus dominates the vagina, and Streptococcus rules the mouth. Every organ is also variable in itself.

The narrative of disease and death still dominates our view of microbiology.

Our diet reshapes the microbes in our gut – could those changes ripple out to affect our minds?

every ten species of arthropods – the animal group that includes insects, spiders, scorpions, mites, woodlice, and more. That is a preposterous proportion! The majority of the 7.8 million or so living animal species are arthropods.

Just as a weed is a flower in the wrong place, our microbes might be invaluable in one organ but dangerous in another, or essential inside our cells but lethal outside them.

It looks like an equitable relationship, until you realise that the tree laces its food with an enzyme that stops the ants from digesting other sources of sugar. The ants are indentured servants. All of these are iconic examples of cooperation, found in textbooks and wildlife documentaries. And each of them is tinged with conflict, manipulation, and deceit.

We have evolved ways of selecting which species live with us, restricting where they sit in our bodies, and controlling their behaviour so they are more likely to be mutualistic than pathogenic. Like all the best relationships, these ones take work. Every major transition in the history of life – from single-celled to multi-celled, from individuals to symbiotic collectives – has had to solve the same problem: how can the selfish interests of individuals be overcome to form cooperative groups?

The immune system’s main function is to manage our relationships with our resident microbes. It’s more about balance and good management than defence and destruction.

Such is the case with inflammatory bowel disease, or IBD.

Herbert “Skip” Virgin published a case study that beautifully supports this idea.

without furry pets were “microbial deserts”. Those with cats were far richer in microbes, and those with dogs were richer still.23 It turned out that man’s best friend is a chauffeur for man’s old friends.

So can two common food additives, CMC and P80, used to lengthen the shelf life of ice cream, frozen desserts, and other processed foods; they also suppress anti-inflammatory bugs.

We know that this happened because Jan-Hendrick Hehemann discovered one of Zobellia’s genes in a human gut bacterium called Bacteroides plebeius.6 The discovery was a total shock: what on earth was a marine gene doing in the gut of a landlubbing human? The answer involves HGT. Zobellia isn’t adapted to life in the gut, so when it