filled with conjectures and hypotheses, this book does provide a fascinating
glimpse into the current state of evolutionary biology. Some things that I got
from this book was a real sense that there is a lot of underlying connectedness
between various diseases, genetic and environmental factors that remains
undiscovered, but which has been the source of speculation for ages. 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
Moalem started out his book by discussing hemochromatosis, which is a buildup
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 buildup 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.
is 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 for
in the past because sugar can act like antifreeze in times of extreme cold. About
13,000 years ago, the retreating glaciers had a sudden reversal that lasted a
thousand years. This period was called the Younger Dryas because pollen from an
Arctic wildflower called Dryas octopetala was found in mud cores dating back to
12,000 years ago. This wildflower only flourished during times of extreme cold.
According to Dr. Moelem it’s possible that the human beings who survived the
Younger Dryas did so because of excess sugar acting as an antifreeze in their
bloodstream. This adaptation might be similar to that of the wood frog’s, which
can freeze solid and then recover completely when the temperature rises to the
right level. One interesting bit of evidence is that those people with a
propensity for diabetes are descended from people who lived in exactly those
places hit by the ice age 13,000 years ago.
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
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.
overall the different diseases discussed in the book really impacted each and
every way of how life works. I learned quite a just reading the book. Too bad I
had to write this during the holiday break though.