Evolutionary Medicine

Ch 17 Homework:

Definition: Evolutionary Medicine is characterized as the integrated study of evolution and medicine aimed at improving scientific understanding of the reasons behind diseases and the actions that can be taken to enhance health.
Core Questions Addressed:
- Why do we get sick?
- Example: Pathogens cause illness as they evolve.
- How can we better prevent and treat diseases?

Host Environment: For human pathogens, the human body serves as the environment that determines their fitness.
- In this environment, specific mutations can be favored through natural selection since they allow pathogens to utilize the host's resources more effectively.
Example of Mutation Effects:
- A virus may develop a mutation enhancing its ability to hijack an infected cell.
- A virus may also acquire mutations that increase its resistance to the host’s pH or digestive chemicals.
Reproductive Success of Mutations:
- The viruses that replicate more effectively than others in the body will increase the frequency of these beneficial mutations within the viral population.
Selective Pressure from Immune System:
- The immune system acts as a selective pressure for pathogens; as the immune system eliminates a population of viruses, it favors mutations that enable these viruses to evade destruction.

Reproductive Scale: Many pathogens reproduce on an extensive scale, leading to rapid population growth.
Mutation Rates: Several pathogens exhibit high mutation rates.
- Errors during genetic replication introduce genetic diversity into the viral population.
- Some viruses lack the necessary enzymes to correct errors that spontaneously occur during replication, leaving new genetic diversity unchecked.

Bacterial Evolution: A species known as Pseudomonas aeruginosa, which is typically free-living, can become pathogenic when it colonizes individuals with cystic fibrosis, leading to the evolution of characteristics suited for survival in the lung environment.
Evolutionary Adaptation in Bacteria:
- Mutations may promote a transition from individual cells into clusters that adhere to the lung lining.
- Additional mutations may enable them to extract iron atoms from the host, optimizing survival in a competitive environment.

Cytomegalovirus Example:
- Cytomegalovirus belongs to the herpesvirus family and typically causes no symptoms in most individuals but can lead to symptoms like swollen glands, fever, and fatigue in some.
Phylogenetic Patterns:
- The branching pattern of cytomegalovirus and its closest relatives aligns with the evolutionary history of their host species, indicating co-speciation for over 30 million years.
Discordance Instances:
- In certain scenarios, the phylogeny of a pathogen does not perfectly reflect that of its host; this discordance can indicate pathogen transfer between species, leading to new diseases.

Question: What does the establishment of Pseudomonas aeruginosa in the lungs of cystic fibrosis patients exemplify?
- Options:
- 1. Rapid evolution in bacteria potentially leading to a pandemic.
- 2. A virulent strain of bacteria becoming less virulent.
- 3. Bacteria jumping from an animal host to a human host.
- 4. Harmless bacteria becoming pathogenic within a host.

Viral Structure: The influenza virus comprises 13 genes organized on eight RNA segments, enveloped by a membrane containing two types of proteins facilitating cell invasion and immune evasion.
Evolutionary Dynamics:
- Influenza can rapidly evolve to evade antibodies as it spreads, often due to mutations that alter the hemagglutinin stalk and surface proteins.
- Antigenic Drift: Characterized by small changes or mutations leading to modifications on the virus’s surface proteins, namely HA (hemagglutinin) and NA (neuraminidase).
Cross-species Transmission: Related to the passage of influenza viruses from wild birds and other mammals to humans.

Reassortment Mechanism: Occurs when two distinct influenza strains infect the same cell, resulting in a genetic reshuffle and production of novel viruses.
Antigenic Shift: Refers to significant changes in viral surface proteins due to reassortment, which may lead to drastic declines in immunity and heightened pandemic potential.

Definition of Resistance: Antibiotic resistance is the ability of pathogens to defend against antibiotics.
Historical Context: The 1940s heralded the discovery of antibiotics as miracle drugs, followed by the evolution of increasing bacterial resistance.
Mechanism of Resistance Development:
- Bacteria that develop mutations enabling them to resist antibiotic action are more likely to survive and reproduce, leading to a greater frequency of resistance mutations within the population.
- Once a beneficial mutation arises, it can quickly spread through a rapidly reproducing bacterial community.
Forms of Antibiotic Resistance:
- Some bacteria block antibiotic entry,
- Some produce enzymes that deactivate drugs,
- Some actively expel antibiotics to minimize harm.

Theory Description: Suggests that certain genes have advantageous effects during early life but negative effects later, influencing the existence of age-related diseases.
- This theory underscores how natural selection may favor genes enhancing reproductive success, despite their potential adverse effects in later life stages.
Historical Background: Proposed by George C. Williams in 1957, emphasizing the trade-offs between benefits during early life and harms in later stages.
Cancer Associations:
- Certain cancer-linked genes illustrate this theory; for instance, mutations in the BRCA1 gene significantly increase breast and ovarian cancer risk in women.
- Studies indicate that women carrying these mutations generally have more children than those with non-harmful BRCA1 variants.