Book Review: Survival of the Sickest by Dr. Sharon Moalem

By Kristy McCaffrey

Survival of the Sickest:

A Medical Maverick Discovers Why We Need Disease

By

Dr. Sharon Moalem with Jonathan Prince

This fascinating read delves into how certain conditions such as cystic fibrosis, diabetes, and high cholesterol may have benefited humans at one time. Evolution favors survival, and in the face of environmental pressures our genes have, at times, given humans the ability to conquer an immediate biological foe only to have that solution work against us in the long term. The book begins with hereditary disorders, and normally such conditions should die out somewhere along the evolutionary line, but many haven’t. Why? Evolution likes genetic traits that help us to survive and reproduce. Anything that doesn’t contribute to this won’t last long in the genetic pool.

Dr. Moalem first examines a condition called hemochromatosis, a hereditary disease that disrupts how the body metabolizes iron. Normally, the body can detect if there is too much iron and will thereby reduce the amount that is absorbed into your intestines, and the excess will pass out of the body. But with hemochromatosis, the body thinks that it never has enough iron, so continues to absorb it. Over time, this can damage joints, major organs, and affect overall body chemistry. Ultimately, it can lead to liver and/or heart failure, diabetes, arthritis, infertility, psychiatric disorders, and even cancer. If nothing is done, death is inevitable.

Surprisingly, however, the gene for hemochromatosis is the most common genetic variant in people of Western European descent. Humans need iron for nearly every function of our metabolism, but so do parasites and cancer cells. In order to keep it away from deadly invaders, our body has iron-related defense mechanisms, such as proteins in our mouth, eyes, noses, ears and genitals that lock up iron molecules and prevent them from being used.

In 1347, the bubonic plague swept through Europe, killing upwards of 25 million people. Not everyone infected died, however. Research has indicated that the more iron in a given population, the more vulnerable they were to the plague. Generally speaking, adult men were at greater risk than malnourished children and the elderly, who were often iron deficient, as well as adult women, who were iron-depleted from menstruation, pregnancy and breast-feeding.

So, what does this have to do with hemochromatosis? People with this condition, while they have too much iron in much of their body, actually have too little inside their white blood cells—the police of our immune systems and the vector that many infectious agents use to feed off iron and multiply. The plague could never get a foothold in these people.

Hemochromatosis is thought to have originated among the Vikings and was spread throughout Europe as they colonized the coastline, and its purpose may have been altogether different initially. But although the condition would have eventually killed them in the long term, it offered short-term protection against the plague. Those who survived reproduced and passed the mutation on to their children. With successive waves of plague breaking out as recently as the nineteenth century, this condition has survived into today’s population. This might also explain why there was never an epidemic as bad as the Black Death of 1347 to 1350, because people with hemochromatosis made up a majority of the survivors, thereby giving subsequent generations protection.

Dr. Moalem analyzed diabetes, specifically Type 1, which is common in people of Northern European descent and appears to have risen during a rapid cool-down of the earth about 13,000 years ago. It turns out that sugar is a natural antifreeze, and the body’s ability to pump a high amount of glucose into the blood may have helped those caught in a sudden ice age to survive. Moalem also touches on cystic fibrosis (carriers of this gene are protected from tuberculosis), childbirth (and why it has evolved to be so dangerous for human females), as well as HIV and aging.

The bottom line is that while evolution is amazing, it’s not perfect, and every adaptation comes with a compromise. This riveting read will change your perspective on disease and the role genetics plays in our lives.

Read Survival of the Sickest at Amazon