Book SummarySurvival of the Sickest, by Sharon Moalem

1-Page Summary1-Page Book Summary of Survival of the Sickest

The evolutionary origins and benefits of genetic disorders

Environmental influences can sometimes transform genetic disorders into unexpected benefits for evolution.

Moalem suggests that although genetic disorders can negatively impact human health, they often persist in populations because of the advantageous evolutionary traits they can offer in certain environmental situations. She highlights the counterintuitive nature of evolution by pointing out the persistent survival of individuals who are afflicted with diseases, a concept that appears to defy logic. She contends that traits which enhance survival and reproductive success are favored by natural selection, despite any associated drawbacks. For example, if a genetic mutation provides resistance to a deadly disease, those who possess this mutation are likely to have an extended lifespan, reproduce, and pass on the trait to their descendants, thus increasing its prevalence within the population.

The mutation that causes hemochromatosis, a disease characterized by excess iron buildup, was selected for in populations exposed to the deadly bubonic plague because it helped the immune system better resist the pathogen

Hemochromatosis is a common genetic disorder that results in the body accumulating an excessive amount of iron, and it is especially common in people of Western European descent. The genetic mutation, once thought to be harmful, might have persisted because it offered an advantage for survival during the devastating bubonic plague epidemics that swept through Europe in the 14th century and continued for centuries after.

Moalem describes how iron constitutes a crucial element for the majority of living organisms, including bacteria. Our bodies have evolved complex mechanisms to control iron levels, implementing measures to limit iron availability during infections, which hinders the growth of pathogens. People with hemochromatosis often find that their macrophages, crucial white blood cells in fighting infections, accumulate iron internally. Macrophages that have reduced amounts of iron are better equipped to combat bacteria that depend on iron for growth, such as the bacterium that causes bubonic plague, Yersinia pestis. People carrying the gene for hemochromatosis were more likely to survive the plague, thus their genetic lineage persisted despite the detrimental impact of having too much iron in the body. Populations that survived the plague saw a marked increase in the frequency of the gene associated with hemochromatosis among their descendants.

Practical Tips

• Create a kitchen herb garden with plants like cilantro, mint, and basil, which can be used to flavor food without relying on iron-rich seasonings. This encourages a diet lower in iron while adding fresh, natural ingredients to your meals.
• Consider incorporating foods that are naturally lower in iron into your diet as a preventive measure. While not a substitute for medical advice, being mindful of iron intake through diet can be a proactive step. Foods like calcium-rich dairy products or eggs can be good options as they can inhibit iron absorption. This is particularly useful if you have a family history suggestive of hemochromatosis.
• Consider using a water filter that removes bacteria but retains minerals, including iron, to maintain a healthy balance in your drinking water.

Other Perspectives

• The mutation could have persisted in the population due to genetic drift or a founder effect, rather than because it conferred a survival advantage during the plague.
• Some pathogens have evolved strategies to circumvent the body's iron withholding mechanisms, which can render the body's efforts less effective in...

Survival of the Sickest Summary Humans and microorganisms have evolved together, each adjusting to their shared surroundings by influencing each other's evolutionary paths.

Infectious diseases have played a substantial role in shaping the trajectory of human evolution.

Moalem emphasizes the crucial influence that the dynamic interaction with microbes has exerted on our evolutionary trajectory, affecting every facet of our physiological constitution and behaviors. Throughout history, humans have evolved protective strategies to counteract the dangers presented by pathogens, which have continuously found novel ways to exploit our physiological systems. The author employs numerous captivating illustrations to show the intricate interactions that have shaped the fates of both humans and microscopic organisms.

Pathogens and parasites have evolved intricate mechanisms to modify the behavior and physiological reactions of their hosts, thereby increasing their own chances of enduring and spreading.

Moalem illuminates the fascinating mechanisms through which parasites and pathogens evolve strategies that manipulate the behavior and physiological conditions of their hosts to serve their own interests. She illustrates this with fascinating instances from nature, including the predatory insect that compels orb weavers to construct unique web...

Survival of the Sickest Summary Genetic and epigenetic changes significantly affect human health and disease.

Our genetic code is dynamic, capable of undergoing alterations that extend beyond mere mutations.

Moalem proposes that our DNA is a flexible structure, not a fixed plan, and it can adjust by silencing, altering, or activating certain genes in response to environmental factors. She introduces the concept that the expression of genes can be affected across multiple generations by environmental elements, even though the DNA sequence itself does not change.

Transposable elements, often referred to as "jumping genes," possess the capability to insert themselves into different positions within the genome, potentially resulting in the switching on or off of specific genes.

Moalem honors a trailblazing geneticist who discovered transposons, DNA segments capable of relocating within the genome. The research conducted by McClintock contested the prevailing belief that genetic information was immutable, showing that, in fact, the genome is flexible and susceptible to alterations, particularly when influenced by environmental factors.

The author explains that transposable elements have the ability to activate or deactivate adjacent genes, thereby altering their expression and...

Survival of the Sickest Summary An evolutionary viewpoint examines the complex relationship between environmental influences, physiological reactions, and evolutionary progress in relation to longevity and patterns of reproduction.

The lifespan of an organism and the pace of its aging process are determined by its genetic composition and the evolutionary forces acting upon it.

Moalem explores the complex subject of aging, proposing that it might be a genetically preordained process influenced by evolutionary forces, as opposed to merely being the result of accumulated damage as time progresses. She explores the trade-offs associated with longer life expectancies, highlighting the delicate balance between the benefits of increased longevity and the resulting heightened vulnerability to diseases, as well as the pressure on available resources.

Cells likely evolved a limit on their division frequency, a strategy intended to protect against cancer, which also contributes to the aging process.

Moalem explores the biological principle that sets a cap on the number of times a cell can split before it loses the ability to do so, a concept referred to as the Hayflick limit. The author proposes that this boundary acts as a robust defense mechanism to prevent the uncontrolled multiplication of cells, potentially resulting in cancer. As cells multiply, their capacity for tissue repair and renewal...