Between Nature and Nurture

10% Human Book Review

Humans have long argued over whether certain characteristics – a propensity for talkativeness, a talent for bowling, a tendency to be disorganized – can best be attributed to nature or nurture. But science writer Alanna Collen, in her book 10% Human, says the game has changed. Now that scientists have ways to examine in detail the microbial life that lives in and on us, she says, “we have a third player, which sits uncomfortably between nature and nurture” – the microbiome.

Collen bases her book title on the common estimation that the human cells in your body are outnumbered by microbial cells nine to one. These microbes, which make up the ‘other 90%’ of you, don’t fit neatly into a category. They are both an environmental factor that changes in response to what you do and where you go (nurture), and a genetic factor that is passed down from your parents, especially your mother (nature).

There’s nothing like a microbial low point to motivate a thorough investigation of the science. For Collen, it came when she was lying in near-constant pain with intravenous antibiotics dripping into her blood after contracting a tick infection in a Malaysian forest. After returning to relative health, Collen wanted to know about the damage her illness and recovery had caused to her microbiome, so she started to familiarize herself with the relevant animal and human research. The resulting book is packed with extensive research and interviews, with insights hidden like gems in the text.

In 10% Human, Collen covers basic human and microbiome biology before posing a central question: Why has the past century brought such a dramatic shift in the types of illnesses affecting humans? Instead of falling prey to infectious diseases like polio and smallpox, people are now suffering from chronic conditions like allergies, autoimmune diseases, digestive issues, brain disorders, and obesity.

Collen doesn’t definitively answer the question, since scientists have yet to answer it, too. But she makes a compelling case that the microbiome – especially in the gut – has something to do with this shift. Collen covers some cutting-edge science on how the gut microbiota relate to the immune system and to excess weight and obesity. A chapter on the gut-brain axis covers a range of findings on microbes’ ability to change behaviour in animals and humans. Then she explores how antibiotics, diet, and birth practices all have the potential to change the microbiota for better or worse. Adept at explaining complex topics like the workings of immune system cells, Collen is strong on biological and historical context for each point.

Collen notes we have gradually embraced many things in our lives that are making us sicker by affecting our microbes. But armed with this information, we can work toward change. She identifies three main factors that have likely been decimating the human microbiota over successive generations: the overuse of antibiotics, a lack of dietary fibre, and a failure to properly seed and nurture the infant microbiota.

But hope is not lost. The final section of the book deals with ways to restore the microbiota – namely, probiotics, prebiotics, and fecal microbiota transplantation. Probiotics, she says, can help treat conditions like hay fever and digestive symptoms, but their real power may be in the difficult-to-study realm of disease prevention. She acknowledges that doctors and scientists are only beginning to learn how to optimize their use in human health.

As the scientific insights continue at a slow burn, we will know more and more about how to prevent and treat diseases related to the microbiota. Says Collen, “Our other 90 per cent are showing us the way to live.”