Survival of the Sickest Summary

Survival of the Sickest

Dr. Sharon Moalem

            Survival of the Sickest is an intriguing book that explores why we need disease. Dr. Moalem asks and answers many questions throughout this book centering on evolution. His main objective in this book was to explain why natural selection selected certain diseases that are harmful to humans nowadays. Throughout his questioning, he reveals to us that the reason so many diseases are still around today is because at some point in history, all of them helped our ancestors to survive and reproduce in their environment. Each chapter in his book focuses on a different aspect of his overall conclusion that modern diseases were beneficial in the past. Each topic gave an example and new understanding of evolution.

            Dr. Moalem started out his book by discussing hemochromatosis, which is a build up of iron in your blood. This relatively rare disease can cause a person to essentially rust to death if left untreated-which is highly possible because it is hard to diagnose. Why would such a disease be around today if it causes death? Moalem explains to us that the build up or iron in your blood can help fight off certain diseases, or plagues. The readers discover that people with hemochromatosis were more resistant to the bubonic plague in the Middle Ages and thus stuck around because it’s carriers passed it on to their offspring. Even though this disease can be harmful, it posed a great advantage to the people affected and thus survived and was selected through evolution.

            Diabetes is also an example of a disease that helped out humanity in the past. The high blood sugar helps keep people warm in the cold. It is believed that diabetes developed during the second Ice Age to help humans survive. The high blood sugar helped lower the freezing temperature of our bodies and aided in the survival of people through the harsh environment. If our blood did not have a high concentration of sugar, it would freeze faster and in doing so create frozen crystals of blood that would slice through our organs, tissue, and cells, killing us. This can also account for the fact that many people have to use the bathroom more when it is cold. You body wants to get rid of as much excess water as possible to lower the freezing point of your body and protect your organs.

            Moalem also presents the idea that some parasites and diseases have an effect on our mental ability when they infect us. They don’t directly control us, but they indirectly affect our behavior and cause us to do things that help them reproduce and spread to other organisms. The degree to which and organism destroys its host is called virulence. This virulence is a factor in our behavior as an affected host. The common cold has a low virulence because it spreads through human contact like sneezing and coughing. It is not a severe virus because it relies on the host to help it reproduce. Things such as malaria and cholera have a high virulence and keep their hosts bedridden because they rely on outside factors to help it spread. Malaria spreads through mosquitoes so it wants you unable to ward off insects and cholera spreads through water supply so it doesn’t care if you can move around. Moalem backs up other scientists in suggesting that we focus on keeping virulence down by eliminating carriers rather than fighting an antibiotic war that he believes we will eventually lose.

            Moalem also discusses epigenetics, the study of heritable changes in gene expression caused by factors other than DNA sequence changes. He talks about methylation, which is the addition of a methyl group to DNA after it has been replicated, causing regulation in gene expression. This explains why a parent and offspring can have different phenotypes even though they have the same genotype. An example of this is the effects of proper prenatal care on a child. If the mother is fit and eats normally during her pregnancy but eats a lot of junk food lacking nutrients, her baby will be prone to obesity. Because the baby does not get correct nutrients in the womb, it prepares for a hostile environment once it is born and programs itself to store fat and nutrients better. When it is born into a world full of proper food, it still has the storage mechanism and so the child becomes overweight even though its parents may not be. Methylation has a large effect on our gene expression.

            Lastly, Moalem explains that the process of aging is probably a planned process to help fight off cancer. It is proposed that each cell has a limit to how much it can divide and then the cell dies, which causes aging. This limit acts a defense against cancer because cancer is a disease cause by uncontrolled cell division. Part of our cellular division limit is caused by telomeres, which are extra material at the end of our genes to keep our genetic material safe. Because division shaves off a bit of our telomeres each time, division is programmed to stop once it reaches the end of the telomere. Most cancer occurs when the enzyme telomerase, which creates telomeres, is activated and erases that limit to division. Without this limit, cancer is inevitable, which is why we all must age and die. (900 words)