If the evolution were so effective, why we still suffered from diabetes, hypertension, high cholesterol, which are related to leading causes of death in US, such as heart disease, stroke and cerebrovascular diseases? It turned out these chronic sicknesses are not bugs, they’re features.
Lesser of two evils
The authors argued these diseases helped the sickest to survive the life-or-deathl situation on the cost of long-term health, — the lesser of two evils.
Your genes are the evolutionary legacy of every organism t/hat 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.
The type I diabetes is an autoimmune disease that the immune system mistakenly attacks pancreas cells where insulin is generated. They are much more commonly identified in the Northern European descents, and the rate dropped as we head south. The hypothesis is the swings of temperature may take decades for the early settlers The genetic defects then had an edge: the high glucose of blood lowers the freezing point to protect internal organs. The brown fat can burn the blood sugar to heat without help of insulin. This will increase the odds for them to survive the cold weather.
The high cholesterol was a solution during the early human migration. The sunlight, more concretely UVB, converts the cholesterol to Vitamin D, and also destroy the folic acid. The homo sapiens grew dark skin to block UVB absorption, and a gene named ApoE4 to crack up cholesterol in the blood to maximize the sunlight usage. Thus we had two knobs to strike the balance. When our ancestors migrated to the north with less sunlight, they evolved with light skin. They had to further boost the cholesterol in high latitude areas such as Northern Europe for the limited sun light.
The high blood pressure, or hypertension is linked to the salt consumption, and how body retain the salt level to regulate the fluid balance. For most inland tribes, salt was a highly-valued trade item or considered as currency. Just fyi, it was regulated by the the imperial China since 221 BC. The capability of retaining relative high salt level is really beneficial, until recently salt becomes a commodity. The hypertension among Africa American, twice as common, was possible due to the unnatural selection of cross-Atlantic slave trade.
Virus, parasites and plague
Hemochromatosis is a common disorder in Western Europe descents in which too much iron is built up in the body. Excess iron can poison organs, lead to liver failure and cancer. The bloodletting therapy popular in the Middle Age did make some sense here. Iron plays an important role for viruses to efficiently replicate within living host cells. Inside hemochromatosis patients’ body, the iron is distributed unevenly, — the white blood cell, macrophage has much less iron than normal. The infectious agents can no longer use it as iron source for reproduction, which suppresses the infection. This poison pill would helped our ancestors to survive the black death.
Parasite is another threating vector, the malaria kills 584,000 people in 2012 alone1. The G6PD deficiency, a genetic disorder which occurs particularly among individuals of Mediterranean background, can cause premature destruction of red blood cells and severe anemia when consuming fava beans. It also disrupts parasite’s life cycle and fends off the malaria.
It is also noting that an adult human contains ten times as many, 1000 different types foreign microbial cells. They live inside us, but not try to kill us because they rely a healthy human body to thrive. So if we made a healthy human body hospitaler than a sick human for the microbes, would this create evolutionary pressures to make them less harmful? Paul W. Ewald researched this topic from evolution biology perspective, trying to solve the arm race of antibiotics.
Pool of genes
In the second half of this book, the authors explored some cutting edge research on genes.
- Less than 3% of human’s DNS contains instruction to build cells.
- Half of the non-coding DNA is made up of jumping genes, aka Transposable elements (TEs) that move from one location on the genome to another. They are essential for the mutations.
- One third of our DNA might come viruses, 8% of human genome is composed of retroviruses and related items.
In million years, the human being have given the microbes the ride of life and borrow some code from their genetic library.
The genes can precisely replicate, to some extend. Leonard Hayflick discovered that cells only divide a fixed number, called Hayflick limit. The aging is again a feature, a biological version of planned obsolescence to avoid cancer.