The Connection between Disease, Evolution, and Life: Survival of the Sickest by Sharon Moalem

Book Review
Survival of the Sickest by Sharon Moalem
Published in 2007 by William Morrow

"DNA isn’t destiny—it’s history. Your genetic code doesn’t determine your life. Sure, it shapes it—but exactly how it shapes it will be dramatically different depending on your parents, your environment, and your choices. 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. And every mutation, every change, that helped them better adapt to their circumstances is written there."

So writes Dr. Sharon Moalem, a geneticist and evolutionary biologist in Survival of the Sickest--the story of how disease is forever linked to our and the Earth's past through evolution.

Why after all, is there, and always has been, so much disease afflicting humanity? From numerous plagues to influenza pandemic to AIDS to cancer millions have died of regardless of space or time.

There will always be disease because of the nature of life: all organisms want to live and reproduce, Dr. Moalem explains. Diseases are caused by bacteria, parasites and viruses, some of which survive by harming humans. Bacteria and viruses reproduce and evolve much faster than humans, and a new strain of either can potentially cause harm to a person or population that doesn't have a built-in response to fight it. That is exactly what happened with the bubonic plague in the 14th century in Europe. However, over time, the plague subsided. Fast forward a couple hundred years and the medicinal practice of bloodletting is widespread on the continent. Fast forward to the late 20th and 21st century and scientists discover that hemochromatosis, afflicting a small but not insignificant number of people with European ancestry, is an inherited disease whose victims die prematurely because of excess iron in their blood. What is the connection between these three events? It turns out that--Sharon Moalem explains--people with hemochromatosis are immune to the bubonic plague (probably caused by the bacterium Yersinia pestis). The downside is that their excess iron will eventually kill them, unless the excess iron is periodically released from the body--via bloodletting! The answer to the whole mystery was evolution: people who had a natural immunity to the bubonic plague were more likely to survive and reproduce, and therefore pass on their hemochromatosis genes onto the next generation.

This is just one amazing story of how evolution plays a role in disease. There are many others discussed by Moalem, including, the reasons why so many northern Europeans inherit a propensity to develop Type 1 diabetes, why malaria victims are bed-ridden, and why mothers affected by malnutrition have babies that can cope better in harsh environments.

The only downside of the book is that the somewhat frequent colloquialisms are unnecessary and written as if the target audience was in middle school. Otherwise, the content of Survival of the Sickest is so engrossing that one is almost guaranteed to pull an all-nighter reading it.