Back in December I read the book “Why We Get Sick” (1992) by Randolph Nesse and George Williams. While some of the information was outdated due to its age, overall I loved the book as it took a more wholistic, evolutionary approach to explaining sickness.
Given the global pandemic of 2019-nCoV (novel coronavirus) underway and the timely nature of my read, here are my brief notes I took from the book.
Why We Get Sick
Two kinds of explanations for disease:
- Proximate explanations — Answer “what” and “how” questions about structure and mechanism. Address how the body works and why some people get a disease and other’s don’t. A proximate explanation describes a trait — its anatomy, physiology, and biochemistry, as well as its development from the genetic instructions provided by DNA.
- Evolutionary explanations — Answer “why” questions about origins and functions. Show why humans, in general, are susceptible to some diseases and not to others. (Or why some parts of the body are so prone to failure.) An evolutionary explanation is about why the DNA encodes for one kind of structure and not some other.
Defenses. Mechanisms our body and immune systems designed specifically to combat an issue. A protective response to a problem. Coughing is a defense. The distinction between defenses and defects is important — defects are not preprogrammed responses, they are results of a problem. Skin turning blue from lack of oxygen is a defect.
Causes of disease:
- Infection. External agents such as bacteria and viruses.
- Novel environments. Environments our evolved bodies aren’t used to handling. A mismatch between our design and our environment.
- Genes. Some of our genes are perpetuated despite the fact the cause disease. In the environments we evolved in, they didn’t harm us enough not to be selected out. DNA can also be mutated and create new bad genes.
- Design compromises. There are costs associated with every major structural change preserved by natural selection.
- Evolutionary legacies. Evolution is incremental and can’t make major changes quickly. Many of the design choices are not optimal and carry on anyway.
Signs and symptoms of infectious diseases
Symptoms of colds and other sicknesses and diseases can be unpleasant. But most of them are useful. It is an adaptation shaped by natural selection specifically to fight infection.
Fever is an adaptation to raise body temperature enough to assist with fighting infection. Body temperature is carefully regulated even during fever; the thermostat is just set a bit higher. Children who take Acetaminophen take about a day longer to recover from chicken pox. There are costs of a fever, of course. Otherwise the body would just always stay at 103F at all times. It depletes nutrient reserves 20% faster and causes temporary male sterility. Still higher fevers can cause delirium and lasting tissue damage. And because regulatory precision is limited, fever will sometimes rise too much and at other times not enough.