The odds against getting cancer are hardly astronomical. The causes, though, can be. Iain Banks, a gifted Scottish author and a friendly acquaintance of mine, was killed this summer after some of the cells of his gall bladder ran amok. In the science fiction that made up about half of his work, Banks had a taste for the cosmic, building artefacts the size of planets or solar systems, chronicling weapons of war capable of destroying suns. And that was the context he chose for the disease which killed him.
"Do you know that I know what caused the cancer?" he asked his friend Stuart Kelly in a last interview for the Guardian. "Cosmic ray. I won’t brook any contradiction; it was a high-energy particle. A star exploded hundreds or thousands of years ago and ever since there’s been a cosmic ray—a bad-magic bullet with my name on it, to quote Ken Macleod—heading towards the moment where it hit one of my cells and mutated it. That’s a science-fiction author’s way to bow out; none of this banal transcription error stuff."
The idea that the atoms of our living bodies were almost all made in stars long dead is a wonder that repetition has reduced almost to a commonplace. First voiced, I believe, by the American astronomer Harlow Shapley, it made its way into the popular imagination through the work of those two great voices of the Sixties, Carl Sagan ("we are all star stuff") and Joni Mitchell ("we are stardust, we are golden"). In Banks’s 1993 novel of life in the face of death, "The Crow Road", it’s the subject of a teenage expatiation on the part of the hero, Prentice McHoan. The author knows it is verging on cliché even if McHoan (stoned at the time) does not—but he still makes it moving. To see his death, like his life, as a gift from the stars was a typically Banksian inversion, dark but playful.
He may have been right. Cosmic rays are subatomic particles which have, for the most part, been accelerated to extreme energies by the sort of magnetic fields produced when a star collapses in on itself, or in the vicinity of a black hole. But for all their outre origins, they are a fact of life on Earth. The magnetic fields of the sun and the Earth provide some protection, but Banks’s DNA, just like everyone else’s, suffered a degree of cosmic-ray damage that sounds quite alarming.
More than 10,000 cosmic rays hit every square metre of the Earth’s surface every second, including the bit that you are sitting, standing or lying on right now. When such rays hit cells they tear electrons from atoms. The resulting chains of chemical havoc damage the molecules nearby—including DNA, if there is any at hand.
When you put it like this, it is hard to see how Banks’s genome, or anyone else’s, survives for any length of time at all. But the cosmic-ray flux is the least of the genome’s problems. While a great deal of the damage done to DNA in human bodies is down to overly reactive chemicals, most do not come from the constant, piercing rain of supernova-remnants and emissaries from the event horizons of black holes. Most of them come from the body’s insistence that its cells use oxygen; respiration of this sort produces the chemicals that can cause damage in much greater amounts than radiation, cosmic or otherwise, does. On average, the DNA in a human cell may be damaged in this way some 10,000 times a day, though estimates vary widely.
Iain Banks lived for 21,662 days—the only number in any of this of which we can be certain. There are a good 10 trillion cells in a human body, maybe more. The number of times his DNA was damaged was thus in the same ballpark as the number of grains of sand on all the beaches of the Earth. It’s a number that outdoes the number of stars in the galaxy by a factor of a billion. It is within spitting distance of the total number of stars in the observable universe.
And here is the really remarkable thing. Ninety-nine point more nines than I can be bothered to type percent of that damage did not kill Iain Banks. It was almost all ceaselessly and seamlessly repaired by machinery quite as amazing as a sky full of stars. This machinery has been evolving since the Sun was young to proofread and repair DNA. In its trillions of tasks it is backed up by yet more machinery designed to kill cells that aren’t repaired satisfactorily and seem set to go rogue. The safeguards on top of safeguards cannot catch absolutely everything. But for the most part what they miss doesn’t matter. Until it does.
And here is the unremarkable thing. That vast number of assaults on any person’s DNA will, if he or she lives long enough, overcome the defences that have been honed for billions of years. This is a reason why, for all the depths of space and time that surround our lives, they mostly end up a similar length, one tiny in the greater scheme of cosmic rays and evolution. A sense of that greater scheme, though, is one of the things that can help a ready mind fill such a life with friendship and feeling and wonder. As Iain did.