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
