Althoughfilled with conjectures and hypotheses, this book does provide a fascinatingglimpse into the current state of evolutionary biology.
Some things that I gotfrom this book was a real sense that there is a lot of underlying connectednessbetween various diseases, genetic and environmental factors that remainsundiscovered, but which has been the source of speculation for ages. Dr.Moalem asks and answers many questions throughout this book centering onevolution. His main objective in this book was to explain why natural selectionselected certain diseases that are harmful to humans nowadays. Throughout hisquestioning, he reveals to us that the reason so many diseases are still aroundtoday is because at some point in history, all of them helped our ancestors tosurvive and reproduce in their environment.
Each chapter in his book focuses ona different aspect of his overall conclusion that modern diseases werebeneficial in the past. Each topic gave an example and new understanding ofevolution.Dr.
Moalem started out his book by discussing hemochromatosis, which is a buildupof iron in your blood. This relatively rare disease can cause a person toessentially rust to death if left untreated-which is highly possible because itis hard to diagnose. Why would such a disease be around today if it causesdeath? Moalem explains to us that the buildup or iron in your blood can helpfight off certain diseases, or plagues. The readers discover that people withhemochromatosis were more resistant to the bubonic plague in the Middle Agesand 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 thepeople affected and thus survived and was selected through evolution.Diabetesis a disease where the body fails to remove excess sugar from the bloodstream.
Dr. Moelem suggests that excess sugar in the blood could have been selected forin the past because sugar can act like antifreeze in times of extreme cold. About13,000 years ago, the retreating glaciers had a sudden reversal that lasted athousand years.
This period was called the Younger Dryas because pollen from anArctic wildflower called Dryas octopetala was found in mud cores dating back to12,000 years ago. This wildflower only flourished during times of extreme cold.According to Dr. Moelem it’s possible that the human beings who survived theYounger Dryas did so because of excess sugar acting as an antifreeze in theirbloodstream. This adaptation might be similar to that of the wood frog’s, whichcan freeze solid and then recover completely when the temperature rises to theright level. One interesting bit of evidence is that those people with apropensity for diabetes are descended from people who lived in exactly thoseplaces hit by the ice age 13,000 years ago.Moalemalso presents the idea that some parasites and diseases have an effect on ourmental ability when they infect us.
They don’t directly control us, but theyindirectly affect our behavior and cause us to do things that help themreproduce and spread to other organisms. The degree to which and organismdestroys its host is called virulence. This virulence is a factor in ourbehavior as an affected host. The common cold has a low virulence because itspreads through human contact like sneezing and coughing. It is not a severevirus because it relies on the host to help it reproduce. Things such asmalaria and cholera have a high virulence and keep their hosts bedriddenbecause they rely on outside factors to help it spread. Malaria spreads throughmosquitoes so it wants you unable to ward off insects and cholera spreads throughwater supply so it doesn’t care if you can move around.
Moalem backs up otherscientists in suggesting that we focus on keeping virulence down by eliminatingcarriers rather than fighting an antibiotic war that he believes we willeventually lose. Moalemalso discusses epigenetics, the study of heritable changes in gene expressioncaused 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 offspringcan have different phenotypes even though they have the same genotype. Anexample of this is the effects of proper prenatal care on a child.
If themother is fit and eats normally during her pregnancy but eats a lot of junkfood lacking nutrients, her baby will be prone to obesity. Because the babydoes not get correct nutrients in the womb, it prepares for a hostileenvironment 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 storagemechanism and so the child becomes overweight even though its parents may notbe. Methylation has a large effect on our gene expression.
Lastly, Moalem explains that the process ofaging is probably a planned process to help fight off cancer. It is proposedthat 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 isa disease cause by uncontrolled cell division. Part of our cellular divisionlimit is caused by telomeres, which are extra material at the end of our genesto keep our genetic material safe. Because division shaves off a bit of ourtelomeres each time, division is programmed to stop once it reaches the end ofthe telomere.
Most cancer occurs when the enzyme telomerase, which createstelomeres, is activated and erases that limit to division. Without this limit,cancer is inevitable, which is why we all must age and die.Sooverall the different diseases discussed in the book really impacted each andevery way of how life works.
I learned quite a just reading the book. Too bad Ihad to write this during the holiday break though.