1. Survival of the Sickest Chapter 3: The Cholesterol Also Rises
By Maddy Van, Piper, and Christiane

2. Chapter Three starts with looking at how the sun affects our bodies on the biochemical level. Natural light from the sun both helps our bodies produce Vitamin D and also destroys the body’s folic acid. In response to this relationship, our bodies have adapted to help protect our folic acid while producing sufficient amounts of Vitamin D.
Introduction

3. Vitamin D
If our bodies don’t have enough Vitamin D, we become vulnerable to osteoporosis in adults and a disease called rickets in children. Once we realized this, we began to put Vitamin D in our milk, but we didn’t have to, because our bodies can produce it for us by converting cholesterol. When our skin is exposed to UVB from the sun, it converts the cholesterol into Vitamin D. Vitamin D is important for the maintenance of calcium and phosphorous levels in our blood. It is also important for the function of the heart, the nervous system, the clotting process, and the immune system.

4. Also called folate depending on what form its in, folic acid helps the body to replicate DNA when cells divide. This is very important during pregnancy, so if the body is low on folic acid during pregnancy the child could have birth defects. It can also cause anemia, because folate helps produce red blood cells.
Folic Acid

5. The Skin
The range of human skin color is due to the amount of sun a population has been exposed to over an extended period of time. The darker your skin, the more protection you have for your folic acid, because the darker it is the more sun your skin absorbs.
When we were evolving, the heat from the sun was destroying our folic acid, which decreased the production of healthy babies, so we adapted darker skin through evolutionary preference.

6. Moving North
When we started moving North, our dark skin because detrimental and began to prevent us from producing the amount of Vitamin D we needed. So, we adapted again, this time for lighter skin.
There is one group of people with dark skin living with little light, however, and they are the Inuit. They have dark skin, but they live in the subarctic. The reason for this, is that they consume large amounts of Vitamin D through fatty fish, which is what their diet mainly consists of.

7. The Trade-Off
For dark skinned people, their color prevented them from building stores of Vitamin D, so what evolution did was it boosted their levels of Cholesterol so the sunlight that does make it through is used efficiently. The same was done for light-skinned people who still couldn’t get enough sunlight. This adaptation also left people with a greater risk for heart disease and stroke. In Caucasians, it has a higher risk for developing Alzheimer's.

8. Alcohol Resistance
Another example of divergent evolutionary paths is the resistance to alcohol for Europeans and people of Asian decent. Half of Asians get a high heart rate, flushed face, and rising temperature after drinking. This is because when humans began to settle, clean water was hard to find, so we tried to find other sources. Europeans used fermentation, and adapted a resistance to alcohol. Asians learned to purify their water by boiling it and making tea, which is why they are less resistant to alcohol.
Milk, which has lactose, is also a beverage that many adults cannot consume without experiencing unpleasant digestive reactions. People who are lactose tolerant are most likely descended from a line of farmers who drank animal milk.