Survival of the Sickest: Chapter 2 Summary & Analysis

Diabetes is one of the most common chronic diseases—in 2007, approximately 171 million people had diabetes. For diabetics, the process through which insulin helps the body use glucose is broken, and sugar in the blood builds up to dangerously high levels. Unmanaged, this can lead to “rapid dehydration, coma, and death.”

There are two major types of diabetes: Type 1 is believed to be an autoimmune disease in which the body’s natural defense system attacks the cells in the pancreas responsible for insulin production. In Type 2 diabetes, the level of insulin production is too low. Moalem writes that it is not fully known what causes diabetes, but genetics is definitely a major contributor. Type 2 diabetes exists across all population groups, but Type 1 diabetes is much more common in people of Northern European descent.

Until about 50 years ago, most people believed that global climate change occurred very slowly. The accepted wisdom was that after the previous ice age, the Earth took a few hundred thousand years to warm up. In 1895, when astronomer Andrew Ellicott Douglass studied tree rings for clues about past climate change, he discovered that there was a century-long climate change that occurred around the 17th century which caused a significant drop in temperature. His findings were dismissed by the scientific community, however.

More evidence of rapid climate change accumulated, as a flower (Dryas octopetala) that is usually found in the Arctic was found in mud cores in Europe 12,000 years ago. This provided evidence for an ice age, which they named the Younger Dryas. By the 1950s and 60s, more evidence was discovered by boring into two-mile cores of ice in Greenland’s glaciers—the equivalent of 110,000 years of climate history. The ice confirmed the existence of the Younger Dryas, a severe drop in temperature which occurred 12,000 years ago and which shockingly took only three years to end. They also showed that the stability of the climate in the last 11,000 years is an exception to the rule, not the norm.

Just before the Younger Dryas, human migration had begun as people moved out of Africa and north into areas in Europe that had been uninhabitable during the previous ice age. But the warming trend ended abruptly, and in just a decade, average temperatures plunged 30 degrees. This likely caused thousands of humans to freeze or starve to death. But some humans survived, and Moalem asks whether some genetic trait might have provided a superior ability to withstand the cold. He also notes that humans likely also adapted socially, moving away from hunter-gatherer societies and instead developing agriculture.

Moalem then explores the effect of cold on humans. While many famous people have had their heads cryogenically frozen in the hopes of one day being reanimated, human tissue doesn’t react well to freezing, as the cold causes blood cells and capillaries to burst. The body does have some defenses against freezing: shivering creates heat, and blood becomes more constricted to the torso to keep vital organs warmer rather than the extremities.

Another adaptation is a specialized heat-generating tissue called brown fat. When blood sugar is delivered to a brown fat cell, it can be converted to heat on the spot, and doesn’t require insulin to do so. Most adults don’t have brown fat—to accumulate it, you need to live in Arctic temperatures for a few weeks and then remain there. One additional reaction to the cold that isn’t fully understood is called cold diuresis: the increased need to pee when it’s cold. 

Moalem next turns to a subject in the plant world: ice wine. Ice wine was supposedly created by accident 400 years ago, when a German vintner’s crop was hit by a sudden frost. The grapes were shrunken and yielded much less juice, but when he pressed them, they were incredibly sweet. The shrunken nature of the grapes was due to water loss, which plants evolved to do in order to protect themselves from freezing. The increased sugar concentration is for the same reason, as sugar is a “natural antifreeze.”

One animal, the wood frog, has also uniquely adapted to the cold. Unlike hibernating mammals that go into a deep sleep in the winter, the wood frog buries itself and freezes solid. It has no heartbeat, breathing, or brain activity while it’s frozen. But minutes after rising temperatures thaw the frog, it sparks into gear and gulps for air. Biochemist Ken Storey studied the frogs and discovered that when the frogs sense the temperature dropping, it moves water out of its blood and pools it in its abdomen. It also dumps glucose into its blood to lower its freezing point. Ice is sandwiched between the skin and muscles, putting them on ice—just as we use ice to transport organs for transplant.

Moalem ties the frogs to humans, noting that the people who have a propensity for diabetes (and thus for high levels of blood sugar) were descended from people who lived in Northern Europe. Any adaptation to manage the cold during the sudden onset of the Younger Dryas, he notes, would have been advantageous. Moalem also argues that they could have developed brown fat, which would allow them to burn off the excess sugar in their blood to generate heat.

There are other bits of evidence to support the theory: for instance, when rats are exposed to freezing temperatures, they become resistant to their own insulin. More diabetics are diagnosed in colder months than warmer months; a study of over 280,000 American veterans with diabetes showed that they had dramatically higher blood sugar levels in colder months. The difference in blood sugar levels was even more pronounced in those who lived in colder climates.

Moalem reaffirms his thesis: that every evolutionary adaptation is a “compromise” between advantage in some circumstances and disadvantage in others. Someone with a diabetes-like condition living in an ice age environment would have limited food, and brown fat would convert excess sugar to heat. Modern-day diabetics, with little or no brown fat and little exposure to the cold, would have no use for the excess sugar. Moalem acknowledges that these connections aren’t definitively confirmed, but that we should still pursue them rather than dismissing them.