Chapter 13: Darwinian MedicineOverview |
The relevance of evolutionary biology to medicine is deep and, in some ways, has only recently begun to be appreciated. Chapter 13 of your textbook explores the evolution of pathogen populations and the evolution of cell populations within individual patients.
13.1 Evolving Pathogens: Evasion of the Host’s Immune Response The fundamental event in evolution is a change in the frequencies of various genotypes within a population. It is with this phenomenon that we begin our discussion of evolution and human health.
Turn to section 13.1 of your textbook to learn about two kinds of evolving populations important in medicine: populations of pathogens, and populations of human cells within individual patients (as in a cancer).
13.2 Evolving Pathogens: Antibiotic Resistance Antibiotics are chemicals that kill bacteria by disrupting particular biochemical processes. For human patients, antibiotics are lifesaving drugs. For populations of bacteria, however, antibiotics are powerful agents of selection. When applied to a population of bacteria, an antibiotic quickly sorts the resistant individuals (those that can tolerate the drug) from the susceptible ones (those that cannot). An evolutionary perspective suggests that antibiotics should be used judiciously; otherwise, these miracle drugs may undermine their own effectiveness.
Refer to section 13.2 of your textbook to learn more about antibiotic resistance.
13.3 Evolving Pathogen: Virulence The final issue we will consider relating to the evolution of pathogen populations is virulence. Virulence is the harm done by a pathogen to the host during the course of an infection. Virulence varies dramatically among human pathogens. Some pathogens, like cholera and smallpox, are often lethal; others, like herpes viruses and cold viruses, may produce no symptoms at all. Evolutionary biologists investigating virulence seek to explain this diversity.
Turn to section 13.3 of your textbook to explore examples of evolving viruses.
13.4 Tissues as Evolving Populations of Cells All of the cells in an individual’s body are descended from a common ancestor, the zygote. If, during the development of a tissue, a mutation occurs in a cell still capable of continued division, then we can think of the tissue as a population of reproducing cells with heritable genetic variation. If one of the genetic variants leads to increased cell survival or faster reproduction, then the tissue will evolve by natural selection, just like a population of free-living organisms.
Refer to section 13.4 of your textbook to learn more about natural selection at the level of cells and tissues.
13.5 The Adaptationist Program Applied to Humans We now shift our focus from pathogen and cell populations that evolve within humans to the human animal itself. Our goal is to illustrate how researchers use the analytical tools of the adaptationist program to understand aspects of human physiology and behavior relevant to medicine and public health. Researchers following the adaptationist program identify traits that appear to be adaptative (see Chapter 9). On the assumption that these traits were produced by natural selection, the researchers formulate and test hypotheses about how the traits enhance fitness.
Refer to section 13.5 of your textbook to learn about investigations in the field of human adaptation.
13.6 Adaptation and Medical Physiology: Fever Many people consider the symptoms that accompany illness to be a nuisance. A common response to the fever associated with a cold or flu, for example, is to take aspirin, acetaminophen, or ibuprofen. These drugs reduce the fever, but they do not combat the virus that is causing the cold or flu. Here we ask whether taking drugs to reduce fever is a good idea. To answer the question, we need to know why people run a fever when they are sick.
Turn to section 13.6 of your textbook to learn about hypotheses about the adaptation of potentially harmful physiologic processes.
13.7 Adaptation and Human Behavior: Parenting In using the adaptationist approach to understand the behavior of humans, evolutionary psychologists adopt the view that the brain is an organ whose properties as a regulator of behavior have been shaped by natural selection. As a regulator of behavior, the brain is a flexible machine, not a computer slavishly converting input to output according to some fixed program. The human brain runs on a complex mix of conscious and unconscious perception, emotion, experience, and calculation, in pursuit of a variety of goals.
Refer to section 13.7 of your textbook to learn about how evolutionary biologists and psychologists consider complex human behavior in light of evolution and adaptation.