Survival of the Sickestexamines illness and survival, genetics and history in a fascinating way, writes Pat Harrold
It is a rare occasion when you come across a scientific writer who can explain complex subjects in a straightforward manner. The late Brendan McWilliams, the meteorological correspondent for this newspaper, had this gift.
Dr Sharon Moalem, the author of Survival of the Sickest, has it too. This book is an extremely readable overview of the place of illness in human evolution. It examines illness and survival, genetics and history in a fascinating way.
The twin tasks of any organism, from a genetic point of view, are to survive and reproduce. So, if natural selection is supposed to get rid of harmful genetic traits, why do we have so many hereditary diseases?
Hemochromatosis is a hereditary disease that disrupts the body's iron balance. Some 30 per cent of us are carriers of the gene, and doctors now routinely screen for the disease. Traditionally, medical science sees such conditions as a perverse anomaly, which must be pursued and extinguished at all costs.
Researchers in the fields of neurogenetics and evolutionary medicine have a different view. Why would something that gives the body a disadvantage hang about for millions of years? Mother Nature is not stupid, just occasionally misunderstood.
Hemochromatosis gives a degree of protection against bubonic plague, which ravaged humanity for decades. So it makes perfect evolutionary sense to have a condition that will kill you in middle age if it ensures your survival in an environment which will kill you long before that.
Once you start thinking like this, the logic becomes obvious. Diabetes, it would seem, has a deep connection with cold. Rapid climate change is the norm, not the exception. The last Ice Age began in a mere 10 years, which was devastating for humanity. (It ended in three years, just in case you are feeling complacent about climate change.)
Sugar is a natural anti-freeze. If a person with a genetic predisposition to diabetes lived in Arctic conditions, with a meagre diet, their higher blood sugar could confer a degree of protection without becoming high enough to kill them. A modern person, in a warm climate, with a Western diet, develops full blown diabetes.
Similarly, African-Americans tend to suffer from high blood pressure. Africans who stayed behind don't have anything like as high an incidence of hypertension. It would appear that the survivors of those who were packed in the slaving ships have a tendency to retain salt, which may have helped their survival, on the journey, but can be a disadvantage in modern times.
All this would come as no surprise to a friend of mine who has maintained for years that the hitherto inexplicable Irish tendency to elect rascal politicians can be attributed to the Famine. He maintains that all the nice Irish died, and the gombeens survived.
Mind you, it is only by an evolutionary twist that the Irish can tolerate an integral part of our make up, which is the ability to drink alcohol. It would appear that when contamination of water was rife (Galwegians can relate to this), westerners brewed and distilled while easterners made tea.
This is why many Asians lack the genetic ability to tolerate alcoholic drinks.
If all this seems revolutionary, when the book gets to the area of DNA, it becomes downright disturbing. For years we thought that our DNA was set at birth, and passed down the generations. In the last five years, research has shown that genetic expression can be switched on and off like a light switch by environmental factors, such as the food we eat and the cigarettes we smoke.
For instance, fat yellow mice who received better antenatal dietary supplements had thin brown babies. This has given rise to a whole sub-discipline called epigenetics, which examines how expression of genes can be altered without changing the DNA. In addition, we have what are known as jumping genes, which appear to promote mutations when times are stressful. In other words, the body has ability to turn specific genes on and off, and even rewrite its own DNA.
In fact, a large proportion of our genetic make up, which used to be known as junk DNA, performs tasks about which we have as yet absolutely no notion.
As Moalem puts it: "There are three billion base pairs of nucleotides in the human genome engaged in a vast and complex dance that makes us who we are. When you try to move one dancer with a bulldozer, you're pretty darn certain to scoop up more than one Rockette." Which all goes to show how daft genetically engineered crops are.
Every medical student should read this book. It may help them realise that humans were not invented by drug companies.
Sharon Moalem is still only 32. He has already discovered a new genetic association for familial Alzheimer's disease. In Survival of the Sickest, his co-author is Jonathan Prince, who used to write speeches for Bill Clinton .
If you are put off by the book's cover, which is inappropriately reminiscent of a Carry On film, check out the website at www.survivalofthesickestthebook.com.
Survival of the Sickest: A Medical Maverick Discovers Why We Need Disease, is published by HarperCollins, price £16.99.