Sample Chapter





Evolution Making Sense Of Life 2nd Edition by Carl Zimmer – Test Bank



Sample  Questions


Test Bank, Chapter 1


  1. Which of the following is NOT an example of evolution?


  • Beak size in a population of birds becomes larger from one generation to the next because larger beaked birds had higher reproductive success and passed the trait to their offspring
  • Over long periods of time whales gradually lost their hindlimbs
  • When traveling to high altitude, human physiology changes to accommodate lower oxygen levels
  • All of the above are examples of evolution


  1. The fluke of a whale and the fluke of a shark:


  • are homologous traits
  • arose through convergent evolution
  • are the result of natural selection
  • b and c are correct
  • all are correct


  1. Mammary glands in whales and humans:


  • are a synapomorphy for these species and other mammals
  • are homologous traits
  • were likely present in the most recent common ancestor of humans and whales
  • all are correct
  • none are correct


  1. Based on current fossil evidence:


  • whales were likely fully aquatic before they evolved peg-like teeth or baleen
  • evolution of baleen forced whales to become fully aquatic
  • the teeth of extinct whales such as Dorudon were similar to those of extinct land mammals
  • a and c are correct
  • b and c are correct


  1. One important feature that links extinct organisms such as Pakicetus and Indohyus to cetaceans is:


  • the shape of a bone in the middle ear
  • the presence of forelimb flippers
  • the lack of hindlegs
  • peg-like teeth
  1. The placement of whales within the artiodactyls is supported by:


  • morphology of limb bones (e.g. the astragalus) in extinct whales
  • DNA evidence
  • the fact that some artiodactyls (e.g. hippos) spend a significant amount of time in the water
  • a and b are correct
  • all of the above


  1. From examining the fossil record, scientists have postulated that long-term historic changes in cetacean diversity depended on:


  • changes in the abundance of diatoms, one of their main food sources
  • changes in the abundance of diatoms, which serve as food for animals that were preyed upon by cetaceans
  • changes in sea temperature
  • rising pollution levels in the ocean
  • changes in the abundance of organisms that prey on cetaceans


  1. Which of the following would explain why viruses such as influenza evolve so rapidly:


  • they have a high mutation rate
  • they have a high replication rate
  • they can undergo viral reassortment
  • none of the above
  • all of the above


  1. Which of the following statements is accurate regarding the evolution of drug resistance in a virus:


  • the drug causes mutations in the virus that make it resistant
  • even before the drug is administered, some virions might be resistant
  • an individual virion that is exposed to the drug will adapt by becoming resistant; future applications of the drug will be ineffective against this virion
  • all of the above


  1. The molecular clock used to date the emergence of the 2009 H1N1 strain would be inaccurate if:


  • mutations arose at different rates in different lineages
  • the most recent common ancestor of the viral strains existed long ago
  • the most recent common ancestor of the viral strains existed recently
  • none of the above
  1. New mutations:


  • are random with respect to their effects on fitness
  • are necessary for natural selection to cause evolutionary change
  • are rare in a population
  • a and b are correct
  • all are correct


  1. Evolution occurs when:


  • individuals in a population change in response to the environment
  • the average value of trait in a population changes from one generation to the next
  • a and b are both correct
  • Neither a or b is correct



Short answer/essay.


  1. Please describe evidence three pieces of evidence found in extant cetaceans that supports the idea that their ancestors had hindlimbs.


  1. During embryonic development hindlimb buds form, but are then stop growing.
  2. Some extant whales have a vestigial pelvis, which only makes sense if their ancestors had hindlimbs.
  3. DNA evidence shows that cetaceans are nested within the artiodactyls. The common ancestor of artiodactyls would have had hindlimbs.


  1. Describe how scientists used carbon isotopes to determine whether extinct whales likely inhabited freshwater or saltwater.


Although most oxygen atoms have eight neutrons, some oxygen isotopes have more (e.g. 10).  Seawater has more oxygen atoms with 10 neutrons (heavy) than freshwater, and animals that live in the sea incorporate more heavy oxygen into their bones than animals that live on land.  Thus, by measuring the ratio of light to heavy oxygen in the bones of fossil whales, and comparing this to ratios found in extant organisms inhabiting freshwater or seawater environments, scientists were able to determine whether extinct whales likely lived in the sea or the land. 





  1. Describe two examples from extant cetacean anatomy or development that reflect their ancestral past.


  1. Vestigial pelvis in some species.
  2. Hindlimb buds form during embryonic development.
  3. Baleen whales have genes for building teeth that have been disabled by mutation.


  1. The influenza virus has only 10 genes, which is far fewer than other non-viral organisms. Why do you think viruses are able to survive and replicate with so few genes compared to other organisms?


Viruses are parasitic, relying on much of the replication machinery of their host to reproduce.  Given this, their genetic code is much smaller and contains fewer genes than other organisms.


  1. When scientists infected vaccinated and non-vaccinated mice with influenza, they found that after nine sequences of viral passage the hemagglutinin protein was altered in one of the groups. Which group was it, and what is the evolutionary explanation for the differences between the groups?


The protein was altered in the vaccinated mice.  Mice that were vaccinated against influenza produced antibodies that recognized the hemagglutinin protein and enabled a swift immune response against infection.  Under these circumstances, a virion that had a mutation altering the structure of the hemagglutinin protein might be able to evade detection by the immune system.  Such virions would have a higher replication rate than those without the mutation.  After several passages, the mutation would be at high frequency in the viral population.  In non-vaccinated mice, selection pressure on the hemagglutinin protein was absent or reduced because newly infected mice did not have antibodies against the protein.  Although there were likely virions in the viral population that had mutations in the hemagglutinin gene, these mutants would not have had a reproductive advantage, and hence would not have increased in frequency in the population. 


  1. Given what you learned about how influenza changes over time, how could you explain the emergence of drug resistance in bacterial pathogens. For example, certain strains of tuberculosis are resistant to many of the major classes of antibiotics traditionally used to fight this pathogen.


There is variation in the bacterial population, with some strains carrying mutations that make them resistant or partially resistant to antibiotics (while other strains do not).  In the presence of antibiotics susceptible strains will die before they reproduce while resistant strains will survive.  If surviving resistant strains pass on the resistant mutation to their progeny, the proportion of the population that is resistant will increase over time. 


  1. The 2009 H1N1 pandemic strain included genes from influenza that normally infects pigs, birds, and humans. How is this possible? Why are mixed strains particularly likely to cause high mortality?


When a host is infected by more than one strain of influenza, the different viral strains can swap genes through the process of viral reassortment.  Reassortant strains can be devastating because surface proteins are very different so the immune system does not recognize the virus.  What is particularly concerning is that reassortment will combine foreign surface proteins from strains that affect other species with the infectious potential of human strains. 


  1. What is a scientific theory and how does this differ from how we often use the term in a non-scientific context?


In a non-scientific context we often use the word theory to describe a hunch or guess.  However, in science the term theory has a very different meaning.  A scientific theory is an overarching explanation for a collection of facts and observations about some major aspect of the natural world.  Theories have been tested repeatedly and are supported by many independent lines of evidence. 


  1. Evolution is often described as a completely random process. Is this true?  Why or why not?


Evolution involves elements that are random and elements that are non-random.  Mutation is random because the likelihood of a particular mutation occurring in a particular individual is based on chance.  Moreover, mutations that would be beneficial in a particular environment are no more likely to occur simply because they would be beneficial.  The process of natural selection is completely non-random as mutations are either lost or preserved based on how they affect the reproductive success of their bearers.  (Note: genetic drift is also random, though at this point in the book the students may not have a strong grasp of this).  



  1. You discover a new 50 million year old fossil that you believe might be an ancient cetacean. The creature looks nothing like a modern cetacean—it has four legs and clearly spent considerable time on land.  Describe one feature that would indicate that this creature was, in fact, an early cetacean.


You could look at the shape of the involucrum, which forms a thick lip made of dense bone in cetaceans but not other mammals (i.e. it is a synapomorphy). 


  1. Describe one piece of evidence that indicates that early four-legged whales such as Indohyus and Pakicetus are more closely related to modern day whales than they are to the closest living four-legged relative of modern whales, the hippopotamus.


Both Indohyus and Pakicetus have an involucrum with a thickened internal lip, a unique feature of whales. 


  1. Sirenians (manatees and dugongs) are aquatic mammals that, like whales, lack hind limbs. Is lack of hindlimbs a homologous trait for sirenians and cetaceans?


No, this would be an example of homoplasy (term not discussed in text) resulting from convergent evolution.   For this to be a homologous trait the common ancestor of sirenians and cetaceans would have also had to lack hindlimbs.  We know that cetaceans are nested within the artiodactyls—since most artiodactyls have four legs, we can conclude that the common ancestor of all artiodactyls probably also had four legs.  Thus, cetaceans would have had to have lost their legs independently from sirenians, to which they are more distantly related.  This is likely a case of convergent evolution producing a similar adaptation to an aquatic lifestyle. 


  1. Before DNA evidence scientists had a difficult time discerning where cetaceans fit into the mammalian family tree. Based on morphological features used to classify artiodactyls, why would it have been difficult to link cetaceans to artiodactyls based on morphological evidence alone? How do more recent discoveries in the fossil record link cetaceans to artiodactyls?


One of the main synapomorphies for the artiodactyls is the pulley-shape of the astragalus, a bone in the ankle.  Modern cetaceans do not have hindlimbs, so there was simply no easy way to link them to the artiodactyls.  The finding that early fossil whales such as Indohyus and Pakicetus have the pulley-shaped astagalus along with derived cetacean features such as the shape of the involocrum, confirms the relationship between these groups. 


  1. Drawing on your knowledge of evolution, describe reasons why treatment and/or vaccination against viruses can be particularly difficult.


  1. Viruses have an extremely high replication rate. Every time a virion replicates there is the possibility for new mutation.  Some of these mutations may change the virus such that it becomes resistant to treatment, or can elude the host immune system.  Having a high replication rate increases the probability of mutations that are beneficial to the virus.
  2. Viruses often have a very high mutation rate. A higher mutation rate increases the probability that some new mutations will be beneficial to the virus. 
  3. Viral reassortment: different viral strains can exchange genetic material. This has similar effects as mutation. It can be particularly problematic for vaccines/treatment because of the possibility of combining novel surface proteins with properties that allow human to human transmission. 

Test Bank, Chapter 3


  1. Lord Kelvin argued that based on the temperature of rocks, the earth could not be as old some geologists thought. What turned out to be wrong with his reasoning?


  • he claimed that the temperature of surface rocks should be used in calcuations, but these calculations were shown to be unreliable
  • he did not realize that the planet’s interior was constantly changing
  • the upper layers of the earth are cooler than Kelvin realized
  • all of the above


  1. Which of the following allowed scientists to determine whether early hominins were browsers (eating shrubs primarily) or grazers (eating grasses primarily)?


  • shrubs and grasses differ in the type of photosynthesis they perform
  • shrubs and grasses have different carbon isotopic signatures
  • fossil remains of plants surrounding hominins indicate what they most likely ate
  • a and b are correct
  • a, b, and c are correct


  1. Scientists discover a new fossil that they expect is at least three million years old. To estimate the age of the fossil they would most likely:


  • search for layers of volcanic ash in rock layers above an below the location of the fossil
  • use radiocarbon dating to determine the age of the fossil itself
  • use radiocarbon dating to determine the age of the sedimentary layer in which the fossil was found
  • all of the above


  1. Minik Rosing and Robert Frei have argued that life likely existed as far back as 3.7 billion years ago. They base this claim on:


  • the presence of biomarkers in rocks of that age
  • fossils of stromatolites in rocks of that age
  • fossils of photosynthetic bacteria in rocks of that age
  • the presence of tiny blobs of mineral-rich fluids in rocks of that age


  1. The earliest generally accepted fossils of living organisms are:


  • yeasts
  • stromatolites
  • zircons
  • carbon isotopes


  1. Eukaryotes differ from archaea and bacteria because:


  • they contain a nucleus
  • the cell membrane contains peptidoglycan
  • they contain mitochondria
  • a and c are correct
  • a, b, and c are correct


  1. The transition of from single-celled to multi-celled organisms:


  • happened once
  • happened on multiple occasions
  • occurred before the origin of eukaryotes
  • a and c are correct
  • b and c are correct


  1. The earliest animal fossils appear similar to modern day:


  • sponges
  • archaea
  • fungi
  • jellyfish


  1. Tetrapods include:
  • organisms descended from ancestors with four limbs
  • birds
  • whales
  • all of the above


  1. The Edicaran fauna includes:


  • organisms that lived on land
  • tetrapods
  • organisms that are not clearly related to any currently existing lineages
  • chordates


  1. Nearly all currently existing animal lineages evolved during which period?


  • Ediacaran
  • Precambrian
  • Cambrian
  • Cryogenian



  1. Prokaryotes include representatives from:


  • bacteria
  • archaea
  • eukarya
  • a and b
  • a, b, and c are all correct


  1. The oldest currently known fossil of a land animal is:


  • a tetrapod
  • a bird
  • a millipede
  • bacteria


  1. Modern day mammals are descended most recently from what group:


  • synapsids
  • reptiles
  • fish
  • amphibians


  1. The diversification of grasses has occurred mostly in the last 20 million years. Some scientists have argued that this can be explained by:


  • the decline of large herbivores
  • the extinction of dinosaurs
  • a decline in the concentration of carbon dioxide in the atmosphere
  • the emergence of insects


  1. The earliest fossils of our own species date to:


  • approximately 500,000 years ago
  • approximately, 2 million years ago
  • approximately 6 million years ago
  • approximately 200,000 years ago




  1. What are four features shared by all chordates?


  1. notochord
  2. hollow nerve chord
  3. pharyngeal gill slits as embryos
  4. post anal tail as embryos


  1. Imagine you discovered a fossil from an adult organism that you suspect might be an ancient chordate. What structure would you look for to confirm you suspicion?


You could look for the presence of a notochord.  Structures such as the pharyngeal gill slits and post anal tail may only be seen in embryos. 



  1. Give one explanation that has been proposed for why grasses expanded and diversified around 20 million years ago.


Around this time the level of carbon dioxide in the atmosphere began to decline.  Grasses perform C4 photosynthesis and are therefore more efficient at extracting carbon dioxide from the atmosphere than C3 plants. 


  1. Match the following species or taxonomic groups with the approximate time period in which they appear in the fossil record:


Bacteria                    3.5 bya

Mammals                  150-200 mya

Tetrapods                370 mya

Flowering plants    132 mya

Sponges                   650 mya


  1. What factor might scientists take into account when choosing an isotope to date a new fossil.


The scientists would need to consider how old the fossil may be relative to the length of the half-life of different radioactive isotopes.  Isotopes with a longer half-life will be better for older fossils, while isotopes with a shorter half-life will be better for younger fossils. 


  1. Describe one advantage that carbon dating provides over other types of radiometric dating.


Dating with other radioisotopes only allows scientists to date rocks.  Thus, the approximate age of fossils has to be estimated based on dates for adjacent layers of volcanic ash.  Carbon dating can be performed on fossils or artifacts themselves, as long as they are not older than about 40,000 years.


  1. Explain how carbon isotopic signatures can be used to determine diets of extinct organisms.


Plants obtain carbon from the atmosphere, which is a mixture of different isotopes (C-13 and C-14).   The carbon becomes incorporated into plant biomass.  Different plants have different carbon isotopic signatures depending on how they perform photosynthesis.  For example, C4 plants have lower levels of carbon -13 than C3 plants.  The ratio of carbon isotopes in animals reflects their diet.  For example, animals that graze primarily on grass would be expected to have less carbon-13 because grasses are C4 plants. By examining the carbon isotopic signature of fossils extinct organisms, and comparing them to signatures found in organisms with a known diet, scientists can get some idea about the diet of the extinct animal.   


  1. Describe an example of where fossils have been used to reconstruct the behavior of extinct animals.


  1. Fossils of ichthyosaurs show some females pregnant, indicating that they gave live birth.
  2. Fossils have been discovered that show one organism in the process of eating another, thus giving an indication of diet.
  3. Fossilized trackways of sauropod dinosaurs indicate migratory patterns and group composition.
  4. Fossils of eggs, hatchlings, and adults demonstrate that some dinosaurs practiced parental care.


  1. Describe three reasons why any given organism would be unlikely to be discovered in fossilized form.


  1. Most organisms are eaten or otherwise degraded to the point where there is nothing left to fossilize.
  2. Fossilization typically requires organisms to be in water and rapidly covered with sediment.
  3. Soft-bodied organisms are unlikely to fossilize.
  4. A fossil must rise to the surface of the earth.
  5. A fossil may be destroyed by erosion
  6. A fossil must be discovered.



Test bank, chapter 11


  1. Muller’s ratchet is the idea that ________ accumulate in asexual populations. In such a situation sex would be beneficial because ___________.


  • deleterious mutations; mutation free genotypes can be recreated through recombination
  • deleterious mutations; it provides protection against parasitism
  • deleterious mutations; more offspring would be produced and thus some are likely to survive
  • beneficial mutations; it would rapidly bring together beneficial mutations from different individuals
  • beneficial mutations; it would increase genetic diversity


  1. The red queen hypothesis proposes that sex to is beneficial because:


  • genetic variation in offspring generated through sex is advantageous in a changing environment
  • sex allows populations to weed out deleterious mutations
  • sex maintains advantageous mutations in populations
  • sexual females are able to produce more offspring than asexuals



  1. Which of the following is not considered a potential benefit of sexual reproduction:


  • separate beneficial mutations can be brought together in a single individual more rapidly
  • recombination allows populations to purge deleterious mutations
  • sex creates variation in offspring, which speeds the evolutionary response to selection
  • sexuals produce twice as many offspring as asexuals



  1. Phalaropes are shore birds with brightly colored females and dull colored males. Females are larger than males and compete with each other for access to males. Considering sexual selection theory, which ideas below seem most plausible in light of the pattern of sexual dimorphism:


  • females incubate the eggs and care for the young
  • males are choosy
  • males incubate eggs and care for the young
  • b and c are correct




  1. The trees below present a hypothetical situation where “T” represents the evolution of a male trait that is attractive to females and “P” represents where the preference in females evolved. Which tree below is consistent with the sensory bias hypothesis? Answer: C


  1. Female stickleback prefer males with brighter red coloration on their belly. Given the results depicted in the graph below, it appears that females that choose redder males benefit from:


  • sensory bias
  • direct benefits
  • good genes
  • nuptial gifts




  1. The graph above shows the relationship between the number of mates and the average number of offspring for males of two different species. Considering this graph:


  • sexual selection on males is predicted to be stronger for species 2; males of species 2 are expected to compete less strongly over access to females
  • sexual selection on males is predicted to be stronger for species 1; males of species 1 are expected to compete less over access to females
  • sexual selection on males is predicted to be stronger for species 2; males of species 2 are expected to compete more strongly over access to females
  • sexual selection on males is predicted to be stronger for species 1; males of species 1 are expected to compete more strongly over access to females


  1. Given the mating systems outlined below, which is most likely to produce sexual conflict:


  • a male and a female partner for life
  • females mate once, males can mate multiple times
  • females and males both mate multiple times
  • none of the above


  1. Pea females prefer peacocks with more eyespots on their tail feathers. The results depicted in the graph above provide support for:


  • sensory bias hypothesis
  • arbitrary choice hypothesis
  • good genes hypothesis
  • good parent hypothesis


  1. According to sexual selection theory, a male signal is likely to be honest if:
  • it exploits a preexisting sensory bias in females
  • it is condition-dependent
  • it is costly to produce
  • a and b are correct
  • b and c are correct


  1. Some species of male water striders forcibly copulate with females. In these species, males are often equipped with exaggerated grasping structures, while females have structures that obstruct the male’s grip. Such a situation could arise through:


  • the Zahavi principle
  • sensory bias
  • intrasexual selection
  • antagonistic coevolution








  1. In an experiment with birds, researchers glued a single long feather onto the head of a group of males (this species does not normally have long head feathers) and left another group unmanipulated. They then allowed males to court females and found that the males with the head feather were more successful at attracting mates than the normal males. This observation seems most relevant to:


  • the good genes hypothesis
  • the sensory bias hypothesis
  • direct benefits
  • intrasexual selection


  1. The arbitrary choice hypothesis requires:


(a) that the male trait is an honest indicator of the male’s overall genetic      quality

(b) that the male trait that the female prefers is heritable

(c) that all offspring of a male with the preferred trait have higher average fitness than the offspring of males without the trait

(d) all answers are correct


  1. Males of some species have proteins in their ejaculate that cause the female to be less attractive to other males for some period of time. Such a trait probably evolved initially through _______, but could also lead to ______ if remating is beneficial for females.


  • male-male competition; sexual conflict and antagonistic coevolution
  • male-male competition; female choice
  • female choice; sexual conflict and antagonistic coevolution

(d) runaway selection; female choice


  1. The opportunity for selection on a trait is greater when:


  • individuals have similar reproductive success
  • individual variation in fitness is large
  • the operational sex ratio is biased
  • a and c are correct
  • b and c are correct








  1. John Endler studied color patterns in guppies that are found in streams in the tropical forests of Venezuela. He noticed that males and females were sexually dimorphic, with males displaying numerous bright spots and other colorations, while females were typically drab in color. However, in natural populations there is considerable variation in the brightness of male coloration, with males in some populations being very bright and males in other populations being less brightly colored.  Endler did a series of experimental studies in natural and artificial environments, where he varied predation pressure by either introducing, or excluding guppy predators.  He found that male guppies from high predation environments became less brightly colored over the course of several generations, while males in low predation environments became more brightly colored.  Based on what you’ve in this chapter, please explain these results.


Given the sexual dimorphism, coloration differences between males and females likely arose through sexual selection. The results of Endler’s experiments suggest that bright coloration is involved in a tradeoff.  In locations with few predators, brightly colored males have higher fitness because they are more attractive to females.  Hence, the average male evolves to be brighter.  In streams with many predators bright coloration may aid in attracting mates but also appears to attract predators.  Females may still prefer brighter males, but the brightest colored males may not survive to reproductive age.  As a result, the average male in the population is more drab compared to populations with fewer predators. 



  1. The graph above shows the reproductive success for males of two different species as a function of the number of mates they obtain. For which species would you expect sexual selection on males to be stronger? Explain your reasoning.


Sexual selection on males is likely stronger in species one.  In species one mating with multiple females greatly increases a male’s fitness, while in species two this effect is minimal.  Furthermore, there appears to be more variation in fitness in species one because some males do not mate at all.  Males of species one would thus benefit more from competing over access to females and the opportunity for selection would be stronger because there is more variance in fitness.  



  1. Only males have large tusks in Asian elephants, and you infer that sexual selection may be involved. Assuming that male tusks are the product of sexual selection, please draw a graph showing the expected relationship between reproductive success and number of mates for both males and females.


Slope of the line for males should be steeper than slope of the line for females.


  1. Explain how the following factors influence sexual selection:


(a) Anisogamy: females invest more into reproduction than males because female gametes are more costly to produce than male gametes.  Because sperm are cheap, and typically in excess, male usually maximize fitness by mating with more females. Males with the highest fitness are those with traits that allow them to outcompete other males.  In contrast, female fitness is not usually limited by access to male gametes, but rather by their own fecundity.  As a result females often do not increase their fitness by mating with multiple males.  Thus, the evolution of traits that allow females to attract more mates is not necessarily favored.


(b) Operational Sex ratio: the operational sex ratio is the ratio of males and females available for reproducing at a given time.  If this ratio is skewed, it can intensify sexual selection.  For example, if the OSR is male biased, then males will experience intense competition for access to mates.  Traits that allow males to outcompete other males will be favored by sexual selection.


(c) Opportunity for selection: the opportunity for selection arises from variance in fitness in a population.  Sexual selection will be stronger on males when there is more variance in male fitness.  If a few males achieve most of the successful fertilizations while other males have no reproductive success, selection on traits that influence these differences is strong.


  1. Please explain the difference between direct and indirect benefits of female choice.


Direct benefits are those that benefit the female through advantages that she, herself, gains.  For example, food, nest sites, or protection all increase the likelihood that a female will survive and/or reproduce.  Indirect benefits are those that affect the quality of the female’s offspring due to inherited genetic traits.


  1. Ivy and Sakaluk (2005) studied the potential benefits of polyandry in decorated crickets. Their experimental design involved the following treatments:
  • Single mated females
  • Three times mated to same male
  • Three times mated to different male


They measured offspring number and offspring survival for each treatment.

How does this experimental design allow the researchers to differentiate between the potential benefits of polyandry (include predictions of they hypotheses)?


Comparisons between (a) and (b and c) allow them to see whether females mating with more than one male benefit at all.  If they do, it could be simply because they get more sperm (sperm limitation) or there could be additional advantages such as increased genetic compatibility or increased probability of getting “good genes.”  If it’s just sperm limitation then the increase in fitness in (a) and (b) should be the same.  If the advantage is increased compatibility or good genes the offspring of (c) should outperform (b).


  1. You perform an experiment to test whether female birds prefer males with longer tail feathers. You find that they do, and, in fact, they prefer even longer tail feathers than you ever see on males in the population. Assuming that this trait has had enough time to evolve to an optimum, what is the most likely explanation for why tail feathers are not even longer in the population?


Tail feathers are costly for the males to produce.  At some point the costs of producing longer tail feathers outweigh the benefits of attracting more mates.  Even though the females might prefer males with even longer tail feathers the net affect on fitness would be negative.   


  1. Describe two costs and two benefits of sexual reproduction.



Twofold cost of sex: sexuals have a reduced replication rate because males do not produce offspring.


Search cost: sexual males and females must expend time and energy finding mates.


Reduced relatedness: sexual organisms pass only half of their alleles to offspring.


Risk of sexually transmitted diseases: sex provides a means of transmission for many pathogens.



Combining beneficial mutations: beneficial mutations present in different individuals can be combined through sex.  In asexual populations this takes more time because a single clone would have to accumulate both mutations randomly.


Generation of novel genotypes: recombination creates gametic diversity, which means offspring are variable.


Faster evolution: offspring of sexuals are more variable, which speeds the evolutionary process and is critical when organisms are coevolving with parasites.


Clearance of deleterious mutations: Because of recombination, sexual populations can purge deleterious mutations.  Asexuals are doomed to accumulate deleterious mutations because they do not undergo recombination.


  1. You are studying the potential for sexual conflict in two species of birds. Species one is monogamous, while males and females of species two both mate multiply. In which species would you expect sexual conflict to be stronger?


Sexual conflict should be stronger in species two.  Monogamy should reduce conflict because the fitness interests of the father and mother are aligned as they both maximize their fitness in the same way.  Any costs to future offspring (or other offspring in a litter) resulting from investment in the focal offspring would accrue equally to the father and mother—thus there is no conflict.  A promiscuous mating system creates the opportunity for conflict because the father does not sire all of the mother’s offspring.   Thus, the father maximizes fitness by influencing the female to produce or invest more into his offspring.  This may result in less investment in future offspring (or other offspring in the litter), but since he is not likely to be the father of those offspring he does not pay the cost.  Overinvestment in his offspring may not maximize the females fitness—hence the conflict.


  1. Please describe two direct benefits and two indirect benefits of female mate choice.


Direct: summarized in Table 11.2

Indirect: summarized in Table 11.3