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

by Ed Yong

‘The problem is that they end up being like the Tarot,’ says Rob Knight. ‘You can tell a good story with any arbitrary combination.’ Imagine that I pulled ten people off the street who are wearing blue shirts and ten who are wearing green shirts. If I ask them enough questions, I guarantee you that I can find at least a couple of striking differences between the two groups. The blue-shirts might prefer coffee while the green-shirts prefer tea. The green-shirts have bigger feet than the blue-shirts. I might propose that blue shirts produce coffee cravings and shrink one’s feet. But if I accosted two groups of a million people each, I’d have a much harder time finding random differences between them, and I’d be more confident that the differences I did see were meaningful. Then again, it takes time and effort to accost a million people. Human geneticists faced the same problem. In the early twenty-first century, when technology hadn’t quite caught up with ambition, they identified many genetic variants that were linked to diseases, physical traits, and behaviours. But once sequencing technology became cheap and powerful enough to analyse millions of samples, rather than dozens or hundreds, many of these early results turned out to be false positives. The human microbiome field is going through the same teething problems.

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