I am impressed with the author's qualifications. He is a scientific researcher while finishing his medical training. The few people I know with such background in my country are raking in millions as the founders in multi-level marketing firms selling health products.
The first chapter I read was fascinating. His grandfather and him both suffer from hemachromatosis. This is a disorder that allows the body to keep building up its storage of iron until an overload may damage the pancreas and the liver, leading to death. His grandfather has been donating blood for most of his life. That apparently is a way to off load iron without harming the body. He went on to describe in details how people with the genetic aberration were favored to survived the Black Death in the middle ages. That was why people descended from Europeans have a one in four chance of inheriting this gene. Not everyone with this defective gene display all the symptoms which would lead to death if untreated. Hence the penetrance of this disorder is low.
The second chapter explains in detail how our bodies react to extreme cold. This in turn has something to do with the way we metabolize glucose. Here I learn of the Hunter's Response: when a person is faced with life threatening cold, his blood vessels would constrict to keep his vital organs warm; after some time in the cold, the constricted capillaries will dilate briefly, sending a rush of warm blood into the numbed fingers and toes before constricting again to drive the blood back into the core. This intermittent cycles of constriction and release would protect both the core organs as well as keeping the limbs from permanent damage. People from warm weather populations do not have this natural ability to protect both their limbs and core at the same time.
In chapter 3 we find him explaining how the sun simultaneously enables us to make vitamin D and destroys folic acid which is required in the making of red blood cells. To protect folic acid, dark skin people has melanin which prevent ultra violet rays from wrecking havoc. To ensure sufficient vitamin D is produced, a gene called ApoE4 cranks up the the amount of cholesterol flowing through the blood to maximize whatever sunlight penetrating the skin. It is interesting to note that ApoE4 is present too in northern Europeans to ensure what little sunlight there is would be fully utilized to make vitamin D.
A common enzyme deficiency, G6PD, is explained in chapter 4. Apparently over many centuries, people carrying G6PD genes were better at surviving malaria. The reason is that their red blood cells are not condusive to host the plasmodium, the shorter life of malformed red cell also disrupts the life cycle of the parasite. Therefore even though folks with G6PD reacts badly to eating fava beans, a staple in Africa and southern Europe, natural selection dictates that this defective gene gets passed onto millions of individuals.
There are four more chapters, each more interesting and thought provoking than the last. This is the first time I encounter evolutionary medicine and it certainly will not be my last.
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