Ed Yong and Adam Rutherford, two of our most exciting science writers, have a knack of upturning everything you think you know about the world. They joined forces to talk about their new books at Dulwich Literary Festival.
Think you’re a self-contained organism? Think again. Half of the cells you carry around with you aren’t even human, says Yong. For roughly every human cell, you host a microbe, a single-celled organism such as a bacterium. What’s more, these ‘germs’ are mostly benign, despite our association of microbes with disease and dirt. Microbes digest our food, construct our immune system, perhaps even affect our moods.
“We rely on microbes for our good health – we are all ecosystems,” he concluded.
As a medical journalist I was familiar with concepts such as the ‘hygiene hypothesis,’ which suggests that the modern day spike in allergies could be caused by our attempts to live in a germ-free environment, confusing our immune systems into identifying harmless substances like pollen or nuts as threats. It was fascinating to hear more – for example that one tenth of breast milk is composed of bacteria, and that gene transfer between gut bacteria and bacteria in food can make digestion of that foodstuff more efficient.
I was less familiar with Rutherford’s work on genetics. To think of the human genome as a blueprint is misleading, he says – it’s best seen as a record, an “epic poem” telling the history of our species. For example, the presence of neanderthal DNA in the human genome means we must have interbred with neanderthal hominids at some point, raising questions about whether they were actually a separate species. More fascinating still, genome analysis of bone fragments from another early hominid suggests a “missing” species, which we only know about because of the traces left in DNA. How many human-like hominids were there before homo sapiens? Excitingly, we are only just beginning to find out.
Looking from the other end of the telescope, Rutherford explained how Richard Branson’s recent claim to be descended from the eighth century Emperor Charlemagne was almost certainly correct – but so are you, if you’re of European heritage, and so am I, and so are many millions beside. Why? Because the most recent common ancestor – the last person from whom all people of European background are descended, Rutherford said, lived only 500 years ago, in the sixteenth century.
The intermeshing of the misleadingly-named ‘family tree’ means most of us are more closely related than we think. He explained that genealogy only identifies those we can find – those who’ve left some records – and misses all of the countless thousands who lived and died without trace. Only in our DNA, he says, can we start to piece together the full human story.
I left the festival with my mind truly boggled, but with a warm glow that came from knowing we have more in common, genetically, than divides us, and we need never feel alone – we’ve got a zoo inside.
I Contain Multitudes, by Ed Yong, is published by Bodley Head
A Brief History of Everyone Who Ever Lived, by Adam Rutherford, is published by Weidenfeld & Nicolson