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The microbiome is changing our concept of self

by Cynthia Macdonald Mar 16 / 18

The microbiome is changing our concept of self
Photo: Andrea Reh, iStock

An anthropologist, entomologist and evolutionary biologist explore the division between our microbes and ourselves

“Nature is what we are put in this world to rise above.” For many of us, Katharine Hepburn’s famous statement in 1951’s The African Queen still holds true. But a growing body of research shows that human bodies are in fact so deeply linked to the natural world that any feelings of superiority we have are clearly misplaced. Might such revelations change the very way we see ourselves?

Tobias Rees thinks so. Rees, a Fellow in CIFAR’s Humans & the Microbiome program, is an anthropologist whose work explores how scientific discoveries are challenging our concept of the human. In a paper entitled “How the Microbiome Challenges the Concept of Self” (published in PLOS Biology and co-authored by Angela E. Douglas and CIFAR Senior Fellow Thomas Bosch), he argues that microbiome research calls into question our established notions of “the self.”

It has long been known that microbes — bacteria, viruses, fungi and archaea — reside on and within us, and are acquired from our interactions with other humans and the environment. But microbes are not merely foreign visitors, says Rees: they’ve been with us from the very start.

“The comprehension of organisms that emerges from microbiome research is that it is best to think of an organism and its microbiome as an evolutionarily conserved, well- integrated unit. Our microbes are a part of our normal physiological processes. For example, when you were an embryo in your mother’s womb, bacterial signals were participating in the development of your embryogenesis,” he says.

Humans have 23,000 genes, 37 per cent of which are microbial in origin. Our microbiome contains a staggering 20 million genes. And, it’s thought that about half of what are now human cells originated as microbes. “Where, given these numbers, does a human end and its microbiome begin?” Rees asks.

We are accustomed to thinking of the immune system as a shield against alien natural invaders; of our genome as a structure that is vulnerable to damage by toxins such as viruses. If, however, our immune system and genome are themselves partially microbial, our relationship to microbial organisms becomes necessarily more complicated. Streptococcus B, for example, can hurt us, but it is also a constant presence within us.

“Where, given these numbers, does a human end and its microbiome begin?”

Our brains are also central to how we define ourselves, yet Rees says the brain, too, is best thought of as part of an integrated human-microbial system. He cites the research of Canadian immunologist John Bienenstock, who recognized that bacteria resident in human intestines “could send signals to the brain. Since then, we have come to recognize that gut bacteria can influence satiety, moods, fear and anxiety”. Many of the processes, in other words, that make up our personalities.

Rees says that the idea that we are “more than mere nature” — qualitatively set apart from animals as special higher-order beings — has not only become untenable but actually destructive, considering the environmental damage for which humans are responsible.

“Indeed, one could plausibly argue that the philosophical concept of the human we have come to live by is complicit with the environmental destruction we are confronted with today. And here, I think, lies one of the reasons why microbiome research is philosophically so important: it is an invitation to think anew, to come up with a different conception of the human.”

“What CIFAR is uniquely good at is finding problems, and gathering a diverse group of experts who would not be talking to each other in a university context.”

The juxtaposition between man and nature has also deeply shaped our educational system, creating a binary where students of the arts learn about the human as a reasoning, conscious “self,” while those who study science or engineering attend to the ‘merely’ natural or to machines.

“However, the question concerning the human — what does it mean to be human? What is our place in the world? — runs diagonal to this somewhat arbitrary division between the humanities and the sciences,” Rees says.

A humanities scholar himself, Rees thinks that the question concerning the human cannot be properly addressed without reform of both the human and the natural sciences. In this respect, he considers that work of the type he does through CIFAR is invaluable.

“What CIFAR is uniquely good at is finding problems, and gathering a diverse group of experts who would not be talking to each other in a university context. For me, working with the Humans & the Microbiome program has been an incredibly enriching experience.”