Ed Yong on the Multitudes within Us

“If we zoomed in on skin, we would see them: spherical beads, sausage-like rods, and comma-shaped beans, each just a few millionths of a metre across.”


I Contain Multitudes: The Microbes Within Us and a Grander View of Life by Ed Yong (2016, Ecco)

In September 2015, I came across a somewhat frightening article on BBC Future called “Is another human living inside you?” by British science journalist David Robson that drew upon a paper on psychological science titled “Humans as Superorganisms: How Microbes, Viruses, Imprinted Genes, and Other Selfish Entities Shape Our Behavior” (July 2015) authored by Peter Kramer and Paolo Bressan of the University of Padua. Robson had extracted the gist of the scholars’ argument in three or four vivid sentences.

First these:

Besides your genes from parents, you are a mosaic of viruses, bacteria – and potentially, other humans. Indeed, if you are a twin, you are particularly likely to be carrying bits of your sibling within your body and brain. Stranger still, they may be influencing how you act.

Then later:

…it has long been known that our bodies are really a mishmash of many different organisms. Microbes in your gut can produce neurotransmitters that alter your mood; some scientists have even proposed that the microbes may sway your appetite, so that you crave their favourite food.

The idea of humans being (or accommodating) more than one entity fascinated me enough to, eventually, make me want to read I Contain Multitudes: The Microbes Within Us and Grander View of Life by the award-winning British science journalist Ed Yong (@edyong209), an alumnus of Cambridge and University College London, who happens to be a staff writer at The Atlantic and blogs at “Not Exactly Rocket Science” on National Geographic. As he takes us on a journey from the visible to the invisible, Yong enlarges the threshold of our perception, greatly enriching and deepening our knowledge of the natural world – and with that, of ourselves.

Song of Myself (1855/92) by Walt Whitman (2001, Dover Publications)

This project on popular microbiology is as poetically marvellous as it is scientifically astute. Forget Orson Welles, who observed ‘We’re born alone, we live alone, we die alone’, instead, says Yong, heed Walt Whitman, who, in his poem Song of Myself (1855) famously declared – ‘I am large, I contain multitudes.’ 

We are legion, each and every one of us. According to the latest estimates, we have around 30 trillion human cells and 39 trillion microbial ones. Our microscopic menagerie is known as a microbiome or microbiota. If our own cells were to mysteriously disappear, this microbiome would perhaps be detectable as a ghostly shimmer, outlining a now-vanished animal core. Microbes (mostly bacteria, also fungi and archaea) live on our skin, inside our guts, inside our very cells. They sculpt our bodies, educate our immune system, help us receive our genes. Our microscopic companions were here before us. (If all of the Earth’s 4.45 billions years of history could be condensed into a year, humans would make their entry at about 11:30 PM on 31st December while bacteria would first appear in mid-March!) Our microbes eat or travel when we eat or travel. When we die, they consume us.

We are entire ecosystems. Archipelagos, really. Yong explains beautifully:

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 Staphylaococcus, while Bacteroides lords over the gut, Lactobacillus dominates the vagina, and Streptococcus rules the mouth. Every organ is also variable in itself. The microbes that live at the start of the small intestine are very different from those in the rectum. Those in dental plaque vary above and below the gum-line. On the skin, microbes in the oily lakes of the face and chest differ from those in the hot and humid jungles of the groin and armpit, or those colonising the dry deserts of the forearms and palms. Speaking of palms, your right hand shares just a sixth of its microbial species with your left hands.


“On the skin, microbes in the oily lakes of the face and chest differ from those in the hot and humid jungles of the groin and armpit…” (Photo: Pixabay)


‘The Father of Microbiology’ – Antony van Leeuwenhoek (1632-1723), Wikipedia

Microbes were first discovered by Anthony van Leeuwenhoek (1632-1723), a Dutch tradesman from the city of Delft who ran a small haberdashery business by day and made lenses by night – this made sense because the Dutch had recently invented both the compound microscope and the telescope. Because Leeuwenhoek wasn’t too keen on passing his technical knowledge to others, the study of microbes was forgotten for almost a century and a half. When microscopic organisms were rediscovered (by figures like Marcus Plenciz, Louis Pasteur, Robert Koch and Joseph Lister), they were immediately cast as “avatars of death.” On account of the damaging activities of a few, all microbes were dubbed as germs, pathogens and bringers of pestilence. Darwin’s “survival of the fittest”, Tennyson’s “nature red in tooth and claw” painted a picture of nature as a domain of constant competition and helped advance the germ theory.

There was another group of biologists, however, working hard to cast microbes in a different light. In reality, the relationship between microbe and animal was a symbiosis (“a neutral living together”) that involved instances of both conflict and harmony.


Common household products like these still make you feel that every bacterium is a germ. (Photo: Lysol Antibacterial Spray Cleaner by User “Mike Mozart”, CC BY 2.0, Flickr)


When the microbe-animal relationship turns from harmony and co-operation to mostly imbalance and discord (symbiosis to dysbiosis), it leads to “diseases” that are interpreted as ecological problems. One example is coral bleaching. (Photo: Bleached coral against normal coral in the Great Barrier Reef by User “Acropora”, CC BY 3.0, Wikipedia)


Yong’s exploration of animal-microbe partnerships is entertaining and informative from start to finish. The part that interested me the most appears in chapter 1 itself. If microorganisms affect hosts in such profound ways, how and where do we draw the line between self and non-self? (this is a big topic in its own right, only tangentially touched in I Contain Multitudes). Microbes shape our individuality but, as Yong points out, they also “subvert” it. A person’s microbiome can supply or withhold substances – this influences their behaviour, including their “social attitudes” and “ability to deal with stress.” Why, doses of bacteria are already being used to treat psychological/mental problems and illnesses.

Are we, then, simply puppets to the biochemistry of our multitudinous inhabitants? What becomes of our ‘free will’ or ‘moral agency’? These are difficult questions with no easy answers. I believe as we continue to learn about and make sense of the complex negotiation between the ecosystems that are humans and their resident microorganisms, we must make sure we don’t end up dissolving the ‘I’ – for then we will be considerably compromising our ability to assess and comment upon the actions of our fellow beings.

Anyway, for now, Ed Yong’s book is a total treat!

Additional Resources:

Ed Yong at the Royal Institution:

Ed Yong at TED:

Featured Image: Pixabay


Preview I Contain Multitudes: The Microbes Within Us and a Grander View of Life by Ed Yong.

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