Deck 20: Evolution and Medicine

Question 1

Viruses are difficult for the immune system to deal with for all of the following reasons, EXCEPT viruses

A) must be located and cleared from infected host cells.
B) have few conserved external structures that the immune system can use to identify them.
C) evolve more slowly than their hosts.
D) are often wrapped in a membrane layer that is nearly identical to the host cell membrane.

Answer 1

C

Question 2

Why is there no lifelong vaccine protection against influenza as there is for measles?

A) Influenza vaccines do not generate an immune response.
B) Influenza can escape host immunity by evolving new variants that reinfect hosts.
C) Influenza is too virulent to effectively vaccinate against.
D) The antigenic memory against influenza has a short half-life.

Answer 2

B

Question 3

Patients with severe bacterial sepsis who develop a fever have higher survival rates than those who do not develop a fever. Does this observation provide causative evidence for the beneficial role of fever in fighting infections?

A) Yes; patients who develop a fever will have a higher mean fitness.
B) Yes; developing a fever is correlated with a strong immune system.
C) No; the disease in patients without fever may have been too severe to allow the body to develop a fever.
D) No; fever has been shown by other studies to be inconsequential in fighting infections.

Answer 3

C

Question 4

Consider Niko Tinbergen's four levels of explanation and complete the following sentence: ________ explanations tell us about the immediate mechanisms that precipitate a particular disease, and ________ explanations tell us how processes such as natural selection leave the body vulnerable to disease.

A) Developmental; phylogenetic
B) Evolutionary; developmental
C) Proximate; evolutionary
D) Phylogenetic; proximate

Question 5

All of the following are true of V(D)J recombination EXCEPT it

A) leads to the production of B-cell antibodies and T-cell receptors.
B) relies on a random process of somatic recombination.
C) can create millions of different receptors by combining a relatively small number of subunits.
D) produces receptors that bind to only nonself proteins.

Question 6

The size difference between most multicellular hosts and their pathogens results in which of the following evolutionary advantages for the pathogen?

A) Pathogens have larger population sizes and shorter generation times than hosts, allowing for increased rates of adaptation.
B) Pathogens have lower mutation rates than hosts, resulting in more stable populations.
C) Hosts evolve more rapidly due to mutations induced by the pathogen.
D) Host population sizes increase in the presence of a pathogen, providing more potential hosts for infection.

Question 7

An increased susceptibility to developing myopia, shortsightedness, is thought to be a consequence of spending time doing "near work," in which the eye is focused on an object, such as a book or computer, less than two feet away. What is the most likely evolutionary explanation for this phenomenon?

A) Natural selection has not had time to catch up with rapid changes in the environment, for example, humans' work environments.
B) Humans are locked in a coevolutionary arms race with pathogens.
C) Natural selection favors reproductive success, even at the expense of vulnerability to disease.
D) Some defenses may be unpleasant to experience, but they are beneficial adaptations rather than maladies.

Question 8

Given that the costs of mounting a fever are less than the benefits, the principle of asymmetric harm predicts that natural selection should result in which of the following?

A) Fevers only occur when an infection has progressed far enough that a fever will be necessary to help clear it.
B) A fever response is mounted more often than it is actually needed to help defend against an infection.
C) frequent cases where fevers would be beneficial but a fever response is not mounted
D) evolution of lower basal body temperatures

Question 9

Which of the following strategies allows vertebrate hosts to counteract the asymmetries in evolutionary rates between most pathogens and their hosts?

A) lateral gene transfer between the host's immune system cells
B) shortened generation times in infected hosts
C) generation of variation and selection on cells of the host's immune system
D) rapid population growth of host organisms

Question 10

All of the following are evolved immune defenses that attempt to isolate pathogens, minimize the harm they cause, and remove them from the body, EXCEPT ________ systems.

A) bacterial restriction modification
B) vertebrate adaptive immune
C) viral reverse transcription
D) plant innate immunity

Question 11

The human immune system detects the presence of pathogens using pattern recognition receptor molecules that bind to common components of pathogens, such as peptidoglycan polymers in cell walls and the flagellin protein of bacterial flagella, known as pathogen-associated molecular patterns, or PAMPs. These receptors are effective because

A) they recognize evolutionarily conserved molecules that are structurally essential to the various bacteria that use them.
B) PAMPs evolve more quickly than other pathogen molecules.
C) they result in rapid evolution of the host immune system.
D) they detect only human immune molecules.

Question 12

Which of the following is an example of a trade-off imposed on an organism that reflects an evolutionary compromise in function?

A) Patients who became infected by a novel flu strain had had no previous exposure to that particular strain.
B) Sturdier bones would prevent fractures but would also reduce an organism's mobility.
C) The crossing of air and food pathways in humans increases the risk of choking.
D) Recent changes in human diet contribute to metabolic diseases.

Question 13

This figure shows the basal and fever temperatures for various vertebrates. If fever conferred only benefits, and had no costs, how might you expect this graph to differ?

A) Basal temperatures would be more like fever temperatures.
B) Fever temperatures would be lower than basal temperatures.
C) Ectotherms would have higher basal temperatures than endotherms.
D) Basal temperatures would be even lower than fever temperatures.

Question 14

Which of the following describes a proximate explanation for fever in mammals?

A) Immune cells recognize the presence of a pathogen and release cytokines, which signal a shift in body temperature.
B) Fevers result in better disease outcomes.
C) Fevers increase metabolic rate and exacerbate tissue damage.
D) Natural selection has tuned the defensive response so fevers are induced even when they may not be needed.

Question 15

The fact that both endothermic and exothermic vertebrates induce fever, by different mechanisms, in response to infection supports which of the following hypotheses?

A) Vertebrates do not experience a coevolutionary arms race with pathogens.
B) All vertebrates are susceptible to infection by the same pathogens.
C) Fever evolved by genetic drift.
D) Fever is adaptive; it may somehow be advantageous in dealing with infection.

Question 16

Which hypothesis for the evolution of sexual reproduction posits that sex is an adaptation for escaping pathogens?

A) good genes hypothesis
B) Red Queen hypothesis
C) mutation accumulation hypothesis
D) rate-of-living hypothesis

Question 17

Experimental infection of lizards with heat-killed bacteria by Linda Vaughn et al. (1974) resulted in behavioral changes that led to ________ in the lizards.

A) higher body temperature
B) increased rates of mortality
C) lower reproductive success
D) increased levels of aggression

Question 18

Which of the following is a mechanism that many pathogens have evolved to subvert the host immune system?

A) down-regulation of various aspects of the innate immune system
B) increased rate of evolution in the host
C) clonal selection and clonal expansion
D) high mutation rate in the adaptive immune system

Question 19

All of the following are steps in the process of clonal selection, EXCEPT

A) immune cells that react with self proteins are deleted.
B) pattern recognition receptor molecules bind to highly conserved components of a pathogen.
C) that when an immune cell binds to an antigen from a pathogen, it proliferates rapidly.
D) recombination generates a diverse immune repertoire.

Question 20

Under which of Randy Nesse and George Williams' evolutionary explanations for disease does the antagonistic pleiotropy hypothesis for senescence fall?

A) Natural selection has not had time to catch up with environmental changes.
B) Natural selection lacks foresight; we are stuck with historically contingent relics of the past.
C) Natural selection favors reproductive success, even at the expense of vulnerability to disease.
D) Some disease symptoms, though unpleasant, are actually beneficial.

Question 21

Which of the following supports the rate-of-living hypothesis?

A) the presence of longevity mutations that confer slower rates of senescence
B) high heritability of life span in many species
C) birds with much longer life spans than mammals of comparable metabolic rate
D) correlation between high longevity and low metabolic rate within a species

Question 22

Plants do not have a germ line and gametes are derived from cell lines that are also responsible for the growth of the organism. Can the disposable soma hypothesis be applied to plants?

A) Yes; trade-offs between reproduction and repair are still possible.
B) Yes; plants have a much higher physiological tolerance for the effects of mutations.
C) No; the distinction between somatic cells and germ line is at the heart of the hypothesis.
D) No; plants do not produce eggs or sperm but rather gametophytes that represent an additional generation.

Question 23

This graph shows a correlation between body mass and longevity for flightless mammals, but bats lie well above the trend line for flightless mammals. Which of the following is likely true based on these data?

A) Flightless mammals experience stronger selection for increased longevity than bats.
B) Bats carry more alleles that experience antagonistic pleiotropy than flightless mammals.
C) Bats have higher metabolic rates than flightless mammals.
D) Bats have lower rates of extrinsic mortality than flightless mammals.

Question 24

How can age-specific antagonistic pleiotropy account for senescence?

A) An allele that confers benefits at a young age might be favored even if it is deleterious at a later age.
B) Mutations that occur early in life are likely to produce more mutations later in life.
C) Early acting mutations are acted on more strongly by selection than late-acting mutations.
D) Alleles that confer benefits early in life also tend to confer benefits later in life.

Question 25

Name Niko Tinbergen's four levels of explanation. Write one question about fever that addresses each level of explanation. Limit your answer to one sentence for each level.

Question 26

What two main factors are responsible for the asymmetry in the coevolutionary arms race between microbial pathogens and their multicellular hosts?

Question 27

What is the likely phylogenetic explanation for the crossing of food and air pathways in humans?

A) A connection between the two previously separated pathways evolved to allow for an alternative air intake in case of a "stuffy nose."
B) Lungs evolved as an extension of the esophagus rather than as a separate organ system.
C) Access to odor receptors in the nose allowed for assessing food quality before swallowing.
D) A connection between both pathways allowed for a more efficient swallowing mechanism.

Question 28

In the survivorship curve shown in the figure, imagine an early acting mutation that increases survivorship between days 0 and 30 and a late-acting mutation that increases survivorship between days 150 and 180. Natural selection will act

A) more strongly on the early acting mutation.
B) more strongly on the late-acting mutation.
C) on both mutations the same.
D) on neither mutation.

Question 29

How does the disposable soma hypothesis account for the abundance of alleles that show antagonistic pleiotropy with respect to age?

A) Alleles that increase the degree of investment in reproduction must also lead to increased investment in repair.
B) There is a fundamental trade-off between investment in reproduction and investment in repair.
C) Because somatic cells are disposable, mutations that affect the soma will not experience selection.
D) Extrinsic mortality results in increased investment in protecting the soma.

Question 30

The mutation accumulation hypothesis for the evolution of senescence proposes that for late-life traits, selection cannot purge deleterious mutations. What assumptions does this hypothesis make?

A) Population sizes are very large and mutations have small fitness effects.
B) Population sizes are finite and mutations have small fitness effects.
C) Population sizes are finite and mutations have large fitness effects.
D) Population sizes are very large and mutations have small fitness effects.

Question 31

This figure shows that the octopus brain wraps around its esophagus so that each bite of food must pass through the middle of its brain. This anatomy is most likely the result of

A) phylogenetic constraint.
B) adaptation.
C) clonal selection.
D) senescence.

Question 32

What is the proximate mechanism for choking?

A) Lungs evolved from pouches in the digestive system.
B) An object gets stuck in the trachea, preventing airflow to the lungs.
C) The epiglottis covers the trachea, so food enters the esophagus.
D) the phylogenetic relationship between fish and mammals

Question 33

Which of the following hypothetical viruses would likely show a "cactus-shaped" population phylogeny?

A) a mutualistic virus that is vertically transmitted
B) a highly virulent virus, like Ebola, that kills its host before the buildup of any immunity
C) a highly virulent virus that results in lifelong immunity and therefore can only infect individuals that have never encountered any of the virus' strains
D) a virus that can reinfect previously infected hosts via escape mutants

Question 34

These graphs show how world-record performance in (A) track and (B) field events vary with age. What phenomenon do these data demonstrate?

A) rate of living
B) senescence
C) age-specific mortality
D) natural selection

Question 35

Asymmetric division in Caulobacter crescentus allowed Ackermann et al. (2003) to measure the reproductive rate of these bacteria relative to their age. This figure shows the age-specific reproductive output for three replicate experiments. What do these data demonstrate?

A) Bacteria can undergo senescence.
B) Bacteria do not contain a germ line and therefore do not age.
C) The reproductive rate of bacteria increases as they age.
D) Reproduction in bacteria does not depend on age.

Question 36

The mutation accumulation and antagonistic pleiotropy hypotheses for senescence both make which of the following predictions about extrinsic mortality?

A) Senescence occurs earlier in populations with higher rates of extrinsic mortality.
B) Senescence occurs later in populations with higher rates of extrinsic mortality.
C) Extrinsic mortality decreases in response to selection for later senescence.
D) Extrinsic mortality rate is not correlated with senescence.

Question 37

Does this graph provide evidence in support of the rate-of-living hypothesis for senescence?

A) No; the rate-of-living hypothesis does not make any predictions about the relationship between metabolic rate and life span.
B) Yes; these data demonstrate that high metabolic rates cause longer life spans.
C) No; the rate-of-living hypothesis predicts that life span should increase with increasing metabolic rate.
D) Yes; this graph shows the expected inverse relationship between metabolic rate and life span.

Question 38

Use one of Randy Nesse and George Williams' evolutionary explanations for vulnerability to disease to explain why you vomit when you get food poisoning.

Question 39

Many wild mushrooms make delicious food, but some are highly toxic and can result in a fatal meal. Apply the principle of asymmetric harm to mushroom identification, and recommend a strategy for mushroom identifiers.

Question 40

Explain how ectothermic animals can produce a fever response.

Question 41

Imagine a population of snails that is polymorphic for sexual reproduction: some lineages are asexual, others reproduce sexually. A new pathogen invades this population and infects both sexual and asexual individuals. If this pathogen is transmitted primarily from parent to offspring, what do you expect to happen to the relative number of sexual and asexual individuals in the population? Why?

Question 42

Figures A and B show the effect of a late- and an early acting mutation on the lifetime fitness of individuals. Reproduction begins at day 30. Using the graphs, how would you determine which of the two mutations had a greater effect on lifetime fitness?

Question 43

Which of the two viral phylogenies below shows the signature of a recent, epidemic population expansion? Explain your answer.

Question 44

Describe the effects of a mutation that displays age-specific antagonistic pleiotropy.

Question 45

Explain why it was beneficial for primitive fish to have a pouch of esophagus or gut tissue that trapped gas bubbles, but why it was problematic for humans.

Question 46

Define pathogen-associated molecular patterns (PAMPs), and explain why they are crucial to a body's immune response against pathogens.

Question 47

Consider an organism that experiences senescence. Draw a graph showing the expected mortality rate (per capita) versus age. Be sure to label your axes (no numerical values are needed) and explain your graph.

Question 48

This figure shows the process of clonal selection and clonal expansion in the vertebrate adaptive immune system. Describe two steps in this process that resemble evolution by natural selection.

Question 49

Name three methods that pathogens use to subvert their host's immune system.

Question 50

This table shows the values for heritability of life span in four different species. Why do these data refute the rate-of-living hypothesis for senescence?