Survival of the Sickest
By Sharon Moalem
William Morrow, 267pp, $32.99
WHY do we get sick? Why do some of us contract hideous diseases that condemn us to misery and shorten our lives? Why are there gruesome inflictions on humanity such as diabetes, sickle-cell anaemia and cystic fibrosis?
If Charles Darwin was right, and all but a radical fringe of creationists believe he was, it follows that evolution should have led to the survival of the fittest. Ergo, after millenniums of evolution, we should all be robust, disease-free human beings, slim and gorgeous, healthy and happy, power-walking effortlessly to work and living until we're 100. Surely we would have bred out those unfortunate people among us susceptible to diseases, and the men and women left behind would be hearty and resistant.
Sharon Moalem claims to have the answer and he details it with great wit and style. These diseases are there, he says, because way back in mankind's evolution they protected our ancestors from premature death, enabling them to live just long enough to procreate.
Moalem isn't the first to posit this thesis. A decade ago, Randolph Nesse and George Williams introduced the revolutionary science of Darwinian medicine, but Moalem brings it to a wider lay audience with his eminently readable and confronting book.
So how is it that today's curses were yesterday's blessings, saving ancestral man from an early environmental death? Today we see diabetes as a disease that is increasingly prevalent in the affluent West, with younger, fatter and more sedentary people suffering its ravages. According to the World Health Organisation, more than 170 million people have diabetes and the number is expected to double by2030.
Yet Moalem says it appeared as a response to the onset of the Ice Age: 13,000 years ago there was a population explosion in northern Europe, where mild temperatures made the land fertile. But a sudden snap freezing, with icebergs in the waters off Spain, caused severe survival problems. Hundreds of thousands froze to death and the population went into severe decline, yet some survived, partly through social adaptation and partly because they had a superior ability to withstand cold.
In very cold weather, we shiver, blood flows away from our skin and we urinate a lot. This loss of water concentrates the blood and, in people with the correct genetic disposition, drives up sugar levels to prevent freezing. In an ice age, this natural anti-freeze prevents death, enabling people to live to an age when they can reproduce and continue the species.
In a warm climate such as ours, it leads to diabetes, but that's an unfortunate side effect: nature has done its work and enabled the anti-frozen couple to produce children.
Moalem uses this type of brazen thinking, backed by solid scientific research, to explain other problems with which humanity has to deal as a result of our evolution from wandering hunter-gatherer to agricultural villager and the long-lived city dweller we've become, people whom nature never intended to live to such oldages. He even explains some anomalies of the Black Death in the 14th century, in which healthy adult men and women were likelier to succumb to the plague than malnourished children, the elderly and pregnant women. It was all due to an evolutionary excess of iron in the blood, a condition known as haemochromatosis.
According to Moalem: "Your genes are the evolutionary legacy of every organism that came before you, beginning with your parents and winding all the way back to the very beginning. Somewhere in your genetic code is the tale of every plague, every predator, every parasite and every planetary upheaval your ancestors managed to survive."
Moalem, who holds a doctorate in neurogenetics, is a confronting and original medical thinker, posing and then answering questions rarely tackled by the traditional medical establishment. Because his entire approach is so solidly grounded in scientific research, perhaps it's time the medical fraternity took notice of our past, as well as our present and our future.
