Evolution: Making Sense of Life Advanced
Prep: Master Evolutionary Biology Practice
Questions & Detailed Explanations
Subject: Evolutionary Biology (Chapters 1–18)
Question 1: In the context of natural selection, how does the concept of "fitness" quantitatively
differ from the colloquial understanding of physical health or vigor?
A) Fitness refers exclusively to the survival rate of an organism until it reaches the age of
reproductive maturity.
B) Fitness is defined by the average contribution of a specific genotype to the gene pool of the
next generation, relative to other genotypes.
C) Fitness is a fixed property of a phenotype, independent of the environmental context or the
presence of competing genotypes.
D) Fitness is maximized when an organism achieves the greatest possible longevity, regardless
of reproductive output.
Correct Answer: B) Fitness is defined by the average contribution of a specific genotype to
the gene pool of the next generation, relative to other genotypes.
Explanation: In evolutionary biology, fitness is a measure of reproductive success (Darwinian
fitness). It is inherently relative to the population's specific environment and the success of
alternative genotypes. Option A is incorrect because survival is only part of the equation;
reproductive success is the ultimate arbiter. Option C is incorrect because fitness is highly
context-dependent (an organism fit in one environment may be unfit in another). Option D is
incorrect because longevity is only beneficial insofar as it contributes to lifetime reproductive
success.
Question 2: Why does the presence of "junk DNA" (non-coding DNA) pose a theoretical
challenge to strict adaptationist views of the genome?
A) It suggests that natural selection is incapable of removing deleterious mutations if they are
located in non-coding regions.
B) It implies that genomic architecture can accumulate neutral or slightly deleterious variations
that are not actively purged by selection.
C) It demonstrates that protein-coding genes are less important for phenotypic evolution than
previously thought.
,D) It proves that all genomic sequences must have a hidden, undiscovered regulatory function
that confers a fitness advantage.
Correct Answer: B) It implies that genomic architecture can accumulate neutral or slightly
deleterious variations that are not actively purged by selection.
Explanation: The neutral theory of molecular evolution posits that much of the variation at the
molecular level is neutral, meaning it does not affect fitness. The accumulation of non-coding
DNA suggests that evolution is not purely a process of optimization by natural selection, but also
involves drift. Option A is incorrect as selection does act on non-coding regions if they influence
fitness (e.g., regulatory elements). Option C is incorrect as the importance of coding genes
remains central to functional biology. Option D represents the "pan-selectionist" view, which
has been largely refuted by the empirical existence of non-functional genomic elements.
Question 3: Consider a population experiencing strong stabilizing selection. How does this
impact the genetic variance of the trait under selection over multiple generations?
A) It increases genetic variance by promoting the accumulation of rare, beneficial mutations.
B) It shifts the mean value of the trait toward the population optimum without affecting variance.
C) It decreases genetic variance by selecting against individuals at the phenotypic extremes.
D) It results in disruptive selection as the population eventually bifurcates.
Correct Answer: C) It decreases genetic variance by selecting against individuals at the
phenotypic extremes.
Explanation: Stabilizing selection acts to favor intermediate phenotypes and selects against
extreme variants. By removing the individuals at the tails of the distribution, the overall
phenotypic and underlying genetic variance in the population is reduced. Option A is incorrect
because stabilizing selection reduces variance, not increases it. Option B is incorrect because
stabilizing selection specifically narrows the variance rather than just shifting the mean. Option
D is incorrect because disruptive selection is the opposite of stabilizing selection.
Question 4: Which of the following best describes the "Red Queen" hypothesis in the context of
host-parasite coevolution?
A) Organisms must constantly adapt and evolve simply to maintain their relative fitness against
ever-evolving biological antagonists.
B) Extinction is inevitable for all species that fail to produce offspring at a rate exceeding their
mortality rate.
C) Sexual reproduction is a disadvantageous strategy because it breaks up favorable gene
combinations.
,D) Parasites always drive their hosts to extinction to maximize their own population growth.
Correct Answer: A) Organisms must constantly adapt and evolve simply to maintain their
relative fitness against ever-evolving biological antagonists.
Explanation: The Red Queen hypothesis suggests that biological systems must constantly evolve
to keep pace with the evolution of other species (especially parasites and pathogens) to avoid
extinction. It is named after the character in Lewis Carroll’s "Through the Looking-Glass" who
states, "It takes all the running you can do, to keep in the same place." Option B is a
misinterpretation of general demographic decline. Option C is incorrect as the Red Queen
hypothesis is frequently used to explain the evolutionary persistence of sex. Option D is incorrect
as parasite fitness is often maximized by maintaining a viable host population.
Question 5: How does the "founder effect" influence the evolutionary trajectory of an isolated
population compared to the source population?
A) It increases the probability of fixation of rare alleles due to the small size of the starting gene
pool.
B) It ensures that the genetic diversity of the new population remains identical to the source
population.
C) It forces the new population to undergo rapid adaptive radiation regardless of the
environment.
D) It eliminates all deleterious recessive alleles that were present in the source population.
Correct Answer: A) It increases the probability of fixation of rare alleles due to the small
size of the starting gene pool.
Explanation: The founder effect occurs when a small group of individuals colonizes a new area.
Because the group is small, it represents only a fraction of the genetic diversity of the source
population. Rare alleles in the source can become disproportionately common (or fixed) in the
founder population due to genetic drift. Option B is wrong because the sampling process
inherently reduces diversity. Option C is wrong because the environment dictates the direction of
selection, not the founder effect. Option D is incorrect as drift is random and can easily increase
the frequency of deleterious alleles.
Question 6: In phylogenetic inference, what is the primary distinction between an apomorphy
and a plesiomorphy?
A) An apomorphy is an ancestral trait, while a plesiomorphy is a derived trait.
B) An apomorphy is a shared trait between all members of a clade, whereas a plesiomorphy is
unique to a single species.
, C) An apomorphy is a derived trait that characterizes a specific clade, while a plesiomorphy is an
ancestral trait shared by a group.
D) Apomorphies are always convergent traits, whereas plesiomorphies are always homologous.
Correct Answer: C) An apomorphy is a derived trait that characterizes a specific clade,
while a plesiomorphy is an ancestral trait shared by a group.
Explanation: Apomorphy refers to a novel, derived trait, whereas plesiomorphy refers to the
ancestral state from which the derived trait evolved. Understanding this distinction is critical for
identifying synapomorphies, which are the basis for determining clade relationships. Option A
reverses the definitions. Option B is incorrect as it confuses synapomorphies with
autapomorphies. Option D is incorrect because both can be homologous; they simply describe
the state of the trait relative to the ancestral condition.
Question 7: How does sexual selection explain the evolution of extreme secondary sexual
characteristics that appear to be deleterious to survival?
A) These traits evolve because they increase the organism's ability to forage for food more
efficiently.
B) These traits act as "honest signals" of genetic quality, meaning only high-quality individuals
can afford the cost of producing them (the Handicap Principle).
C) These traits are strictly the result of genetic drift and have no relationship to mate preference.
D) These traits provide protection against predators through mimicry.
Correct Answer: B) These traits act as "honest signals" of genetic quality, meaning only
high-quality individuals can afford the cost of producing them (the Handicap Principle).
Explanation: The Handicap Principle, proposed by Amotz Zahavi, suggests that costly traits (like
the peacock's tail) serve as signals of fitness. Because they are costly, only individuals with good
genes can survive despite them, making them reliable indicators for mate choice. Option A is
incorrect as these traits usually decrease survival. Option C is incorrect because sexual selection
is a distinct, non-random process. Option D is incorrect as these traits often make individuals
more conspicuous to predators.
Question 8: Why is "convergent evolution" a significant confounding factor in reconstructing
accurate phylogenetic trees?
A) It causes distantly related species to appear closely related due to the independent evolution
of similar traits.
B) It masks the true relationships by causing closely related species to lose their shared ancestral
traits.
Prep: Master Evolutionary Biology Practice
Questions & Detailed Explanations
Subject: Evolutionary Biology (Chapters 1–18)
Question 1: In the context of natural selection, how does the concept of "fitness" quantitatively
differ from the colloquial understanding of physical health or vigor?
A) Fitness refers exclusively to the survival rate of an organism until it reaches the age of
reproductive maturity.
B) Fitness is defined by the average contribution of a specific genotype to the gene pool of the
next generation, relative to other genotypes.
C) Fitness is a fixed property of a phenotype, independent of the environmental context or the
presence of competing genotypes.
D) Fitness is maximized when an organism achieves the greatest possible longevity, regardless
of reproductive output.
Correct Answer: B) Fitness is defined by the average contribution of a specific genotype to
the gene pool of the next generation, relative to other genotypes.
Explanation: In evolutionary biology, fitness is a measure of reproductive success (Darwinian
fitness). It is inherently relative to the population's specific environment and the success of
alternative genotypes. Option A is incorrect because survival is only part of the equation;
reproductive success is the ultimate arbiter. Option C is incorrect because fitness is highly
context-dependent (an organism fit in one environment may be unfit in another). Option D is
incorrect because longevity is only beneficial insofar as it contributes to lifetime reproductive
success.
Question 2: Why does the presence of "junk DNA" (non-coding DNA) pose a theoretical
challenge to strict adaptationist views of the genome?
A) It suggests that natural selection is incapable of removing deleterious mutations if they are
located in non-coding regions.
B) It implies that genomic architecture can accumulate neutral or slightly deleterious variations
that are not actively purged by selection.
C) It demonstrates that protein-coding genes are less important for phenotypic evolution than
previously thought.
,D) It proves that all genomic sequences must have a hidden, undiscovered regulatory function
that confers a fitness advantage.
Correct Answer: B) It implies that genomic architecture can accumulate neutral or slightly
deleterious variations that are not actively purged by selection.
Explanation: The neutral theory of molecular evolution posits that much of the variation at the
molecular level is neutral, meaning it does not affect fitness. The accumulation of non-coding
DNA suggests that evolution is not purely a process of optimization by natural selection, but also
involves drift. Option A is incorrect as selection does act on non-coding regions if they influence
fitness (e.g., regulatory elements). Option C is incorrect as the importance of coding genes
remains central to functional biology. Option D represents the "pan-selectionist" view, which
has been largely refuted by the empirical existence of non-functional genomic elements.
Question 3: Consider a population experiencing strong stabilizing selection. How does this
impact the genetic variance of the trait under selection over multiple generations?
A) It increases genetic variance by promoting the accumulation of rare, beneficial mutations.
B) It shifts the mean value of the trait toward the population optimum without affecting variance.
C) It decreases genetic variance by selecting against individuals at the phenotypic extremes.
D) It results in disruptive selection as the population eventually bifurcates.
Correct Answer: C) It decreases genetic variance by selecting against individuals at the
phenotypic extremes.
Explanation: Stabilizing selection acts to favor intermediate phenotypes and selects against
extreme variants. By removing the individuals at the tails of the distribution, the overall
phenotypic and underlying genetic variance in the population is reduced. Option A is incorrect
because stabilizing selection reduces variance, not increases it. Option B is incorrect because
stabilizing selection specifically narrows the variance rather than just shifting the mean. Option
D is incorrect because disruptive selection is the opposite of stabilizing selection.
Question 4: Which of the following best describes the "Red Queen" hypothesis in the context of
host-parasite coevolution?
A) Organisms must constantly adapt and evolve simply to maintain their relative fitness against
ever-evolving biological antagonists.
B) Extinction is inevitable for all species that fail to produce offspring at a rate exceeding their
mortality rate.
C) Sexual reproduction is a disadvantageous strategy because it breaks up favorable gene
combinations.
,D) Parasites always drive their hosts to extinction to maximize their own population growth.
Correct Answer: A) Organisms must constantly adapt and evolve simply to maintain their
relative fitness against ever-evolving biological antagonists.
Explanation: The Red Queen hypothesis suggests that biological systems must constantly evolve
to keep pace with the evolution of other species (especially parasites and pathogens) to avoid
extinction. It is named after the character in Lewis Carroll’s "Through the Looking-Glass" who
states, "It takes all the running you can do, to keep in the same place." Option B is a
misinterpretation of general demographic decline. Option C is incorrect as the Red Queen
hypothesis is frequently used to explain the evolutionary persistence of sex. Option D is incorrect
as parasite fitness is often maximized by maintaining a viable host population.
Question 5: How does the "founder effect" influence the evolutionary trajectory of an isolated
population compared to the source population?
A) It increases the probability of fixation of rare alleles due to the small size of the starting gene
pool.
B) It ensures that the genetic diversity of the new population remains identical to the source
population.
C) It forces the new population to undergo rapid adaptive radiation regardless of the
environment.
D) It eliminates all deleterious recessive alleles that were present in the source population.
Correct Answer: A) It increases the probability of fixation of rare alleles due to the small
size of the starting gene pool.
Explanation: The founder effect occurs when a small group of individuals colonizes a new area.
Because the group is small, it represents only a fraction of the genetic diversity of the source
population. Rare alleles in the source can become disproportionately common (or fixed) in the
founder population due to genetic drift. Option B is wrong because the sampling process
inherently reduces diversity. Option C is wrong because the environment dictates the direction of
selection, not the founder effect. Option D is incorrect as drift is random and can easily increase
the frequency of deleterious alleles.
Question 6: In phylogenetic inference, what is the primary distinction between an apomorphy
and a plesiomorphy?
A) An apomorphy is an ancestral trait, while a plesiomorphy is a derived trait.
B) An apomorphy is a shared trait between all members of a clade, whereas a plesiomorphy is
unique to a single species.
, C) An apomorphy is a derived trait that characterizes a specific clade, while a plesiomorphy is an
ancestral trait shared by a group.
D) Apomorphies are always convergent traits, whereas plesiomorphies are always homologous.
Correct Answer: C) An apomorphy is a derived trait that characterizes a specific clade,
while a plesiomorphy is an ancestral trait shared by a group.
Explanation: Apomorphy refers to a novel, derived trait, whereas plesiomorphy refers to the
ancestral state from which the derived trait evolved. Understanding this distinction is critical for
identifying synapomorphies, which are the basis for determining clade relationships. Option A
reverses the definitions. Option B is incorrect as it confuses synapomorphies with
autapomorphies. Option D is incorrect because both can be homologous; they simply describe
the state of the trait relative to the ancestral condition.
Question 7: How does sexual selection explain the evolution of extreme secondary sexual
characteristics that appear to be deleterious to survival?
A) These traits evolve because they increase the organism's ability to forage for food more
efficiently.
B) These traits act as "honest signals" of genetic quality, meaning only high-quality individuals
can afford the cost of producing them (the Handicap Principle).
C) These traits are strictly the result of genetic drift and have no relationship to mate preference.
D) These traits provide protection against predators through mimicry.
Correct Answer: B) These traits act as "honest signals" of genetic quality, meaning only
high-quality individuals can afford the cost of producing them (the Handicap Principle).
Explanation: The Handicap Principle, proposed by Amotz Zahavi, suggests that costly traits (like
the peacock's tail) serve as signals of fitness. Because they are costly, only individuals with good
genes can survive despite them, making them reliable indicators for mate choice. Option A is
incorrect as these traits usually decrease survival. Option C is incorrect because sexual selection
is a distinct, non-random process. Option D is incorrect as these traits often make individuals
more conspicuous to predators.
Question 8: Why is "convergent evolution" a significant confounding factor in reconstructing
accurate phylogenetic trees?
A) It causes distantly related species to appear closely related due to the independent evolution
of similar traits.
B) It masks the true relationships by causing closely related species to lose their shared ancestral
traits.
