Evolution

142 questions

All types142 Multiple choice76 True / False14 Matching26 Ordering26

Match each paleontological discovery or fossilization phenomenon listed under Fossil Evidence with its corresponding evolutionary significance or geological application listed under Significance.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Seymouria fossil records match with 'Represents a critical transitional form displaying anatomical features intermediate between amphibians and early reptiles'; Permineralization process matches with 'Involves precipitation of mineral ions into porous organic cavities, preserving cellular microstructure'; Stromatolites match with 'Provides fossilized sedimentary evidence of ancient microbial mats representing early Precambrian cellular life'; Potassium-argon decay system matches with 'Serves as an absolute dating method for igneous rock strata enclosing ancient hominid and early vertebrate fossils'.

Each item accurately connects a specific paleontological phenomenon with its core evolutionary or geological application. Seymouria represents the amphibian-reptile transition; permineralization describes mineral deposition into cellular spaces; stromatolites demonstrate early Precambrian life; and potassium-argon dating provides absolute ages for ancient volcanic rock strata.

Step-by-Step Solution

Analyze transitional fossil specimens

Identify Seymouria as a classic transitional fossil bridging amphibians and reptiles.

Transitional forms provide physical evidence of macroevolutionary species divergence.

Examine fossil preservation mechanisms

Connect permineralization to the influx of mineralized water filling cell spaces without replacing the cell wall material entirely.

Different preservation modes tell us about environmental conditions at the time of fossilization.

Identify Precambrian fossil evidence

Link stromatolites to cyanobacterial microbial mat formations in ancient marine strata.

Stromatolites establish the baseline geological timeline for early cellular life on Earth.

Differentiate radiometric dating techniques

Match potassium-argon (

^{40}\text{K}/^{40}\text{Ar}

) dating to volcanic/igneous rock layer dating over long geological timescales.

Because carbon-14 has a short half-life (

5{}730

years), potassium-argon (half-life

\approx 1.25 \times 10^9

years) must be used for older fossil-bearing volcanic strata.

Key Concept

Paleontological Evidence for Evolution

Question 42Question →

According to Jean-Baptiste Lamarck's theory of evolution, an organ subjected to continuous and increased functional demand during an organism's lifetime undergoes structural hypertrophy, and this acquired modification is directly transmitted to subsequent generations.

True

False

Show answer & explanation

Answer: True

Answer

True. Lamarck's evolutionary model explicitly combines organ development through functional use (hypertrophy) with the transgenerational inheritance of acquired physical characteristics.

The statement is true because Jean-Baptiste Lamarck's evolutionary mechanism fundamentally relies on two interconnected ideas: that increased functional demand causes organ development and hypertrophy within an organism's lifetime, and that these acquired somatic traits are preserved and passed to offspring.

Step-by-Step Solution

Examine Lamarck's first postulate concerning organ modification during an individual's lifetime.

Lamarck proposed that increased environmental need leads to increased organ usage, resulting in physical enlargement and enhanced development (hypertrophy) of the affected somatic structure.

This establishes the principle of use and disuse within an organism's lifespan.

Examine Lamarck's second postulate concerning transgenerational transmission.

Lamarck asserted that physical changes acquired by an individual through use or disuse during its lifetime are directly inherited by its progeny.

This links individual somatic adaptation to evolutionary changes across generations.

Evaluate the accuracy of the statement against Lamarckian theory.

The statement correctly combines both fundamental postulates of Lamarckism without introducing modern genetic concepts.

Confirms the statement as true.

Key Concept

Lamarck's Postulates of Use/Disuse and Inheritance of Acquired Traits

Question 43Question →

According to modern evolutionary theory (Neo-Darwinism), which mechanism serves as the ultimate source of new genetic variations upon which natural selection acts?

Gene mutations that alter DNA sequences

Somatic adaptations acquired through use and disuse during an organism's lifetime

Non-heritable environmental modifications of continuous phenotypic traits

Functional adjustments made by analogous structures in response to habitat demands

Show answer & explanation

Answer: Gene mutations that alter DNA sequences

Answer

Gene mutations that alter DNA sequences serve as the ultimate source of new genetic variations in Neo-Darwinism.

Modern evolutionary theory (Neo-Darwinism) establishes that random gene mutations (along with genetic recombination) generate new alleles. Natural selection then acts upon this heritable genetic variation.

Step-by-Step Solution

Identify the primary source of genetic variation in population genetics.

Gene mutations create brand-new alleles within the gene pool.

Modern evolutionary theory unites Darwinian natural selection with Mendelian genetics, establishing that mutations produce genetic novelty.

Distinguish heritable genetic changes from non-heritable modifications.

Only changes in germline DNA (gene mutations) are inherited by subsequent generations.

Acquired somatic traits or environmental phenotypic shifts do not alter germ cells.

Key Concept

Gene Mutation as the Source of Evolutionary Variation

Question 44Question →

A paleontologist inspects an undisturbed sedimentary sequence containing two distinct volcanic ash layers: Layer $X$ (the lower bed) and Layer $Y$ (the upper bed), which encapsulate an intermediate fossiliferous sedimentary stratum. Mass spectrometry reveals that potassium-bearing minerals in Layer $X$ have a $^{40}\text{K}$ to $^{40}\text{Ar}$ ratio of $1:3$ , whereas minerals in Layer $Y$ have a $^{40}\text{K}$ to $^{40}\text{Ar}$ ratio of $1:1$ . Given that the half-life of $^{40}\text{K}$ is $1.3 \times 10^9\text{ years}$ , which of the following deductions regarding the age and geological significance of the fossil in the intermediate layer is correct?

The fossilized organism existed between

1.3 \times 10^9

and

2.6 \times 10^9

years ago, bounded by absolute radiopaque ages of the surrounding strata based on the law of superposition.

The fossilized organism existed between

0.65 \times 10^9

and

1.3 \times 10^9

years ago because radio-isotopic decay rates accelerate in deeper geological layers due to environmental pressures.

The fossilized organism is older than

2.6 \times 10^9

years because upper volcanic ash beds indicate primary ecological succession over older underlying fossil beds.

The fossilized organism must be classified as an analogous transitional form because identical radiometric ratios reflect functional rather than chronological relationships.

Show answer & explanation

Answer: The fossilized organism existed between $1.3 \times 10^9$ and $2.6 \times 10^9$ years ago, bounded by absolute radiopaque ages of the surrounding strata based on the law of superposition.

Answer

The fossilized organism existed between

1.3 \times 10^9

and

2.6 \times 10^9

years ago, bounded by absolute radiopaque ages of the surrounding strata based on the law of superposition.

Layer X contains a

1:3

ratio of

^{40}\text{K}

^{40}\text{Ar}

, meaning

25\%

of the parent isotope remains, corresponding to two half-lives (

2.6 \times 10^9\text{ years}

). Layer Y contains a

1:1

ratio, meaning

50\%

of the parent isotope remains, corresponding to one half-life (

1.3 \times 10^9\text{ years}

). Under the law of superposition, sedimentary strata between two dated volcanic beds fall chronologically between those bracketed age limits.

Step-by-Step Solution

Determine the age of lower Layer X using half-life calculation

Ratio

^{40}\text{K}:^{40}\text{Ar} = 1:3

indicates that

1/4

(

25\%

) of the original

^{40}\text{K}

remains. This corresponds to

2

half-lives:

2 \times 1.3 \times 10^9 = 2.6 \times 10^9\text{ years}

When

^{40}\text{K}

decays into

^{40}\text{Ar}

, the total initial parent quantity equals parent plus daughter products (

1 + 3 = 4

). Remaining fraction is

1/4 = (1/2)^2

Determine the age of upper Layer Y using half-life calculation

Ratio

^{40}\text{K}:^{40}\text{Ar} = 1:1

indicates that

1/2

(

50\%

) of the original

^{40}\text{K}

remains. This corresponds to

1

half-life:

1 \times 1.3 \times 10^9 = 1.3 \times 10^9\text{ years}

Total initial parent quantity is

1 + 1 = 2

. Remaining fraction is

1/2 = (1/2)^1

Apply the Law of Superposition to place the fossil in time

Since Layer X is below the fossil stratum and Layer Y is above it, the fossil is older than Layer Y (

1.3 \times 10^9

years) and younger than Layer X (

2.6 \times 10^9

years).

In undisturbed sedimentary rock sequences, deeper rock layers are older than superior rock layers.

Key Concept

Integration of Radiometric Dating and Stratigraphic Superposition in Paleontology

Question 45Question →

A population of bacteria exhibits variation in antibiotic resistance traits. Arrange the following events describing the evolutionary process of antibiotic resistance according to Darwin's theory of natural selection in the correct chronological sequence, from first to last.

Drag items to arrange them in the correct order

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Answer

The correct chronological sequence is: 1) Pre-existing variation in resistance traits, 2) Overproduction leading to competition, 3) Antibiotic selection causing differential survival, 4) Inheritance of resistance traits through reproduction, 5) Shift in population trait frequency.

Darwin's theory of natural selection operates through a strict logical progression. First, pre-existing variations arise spontaneously in the population. Second, overproduction of offspring leads to competition for limited resources. Third, an environmental selective agent (such as an antibiotic) causes differential survival, favoring individuals with advantageous traits. Fourth, survivors reproduce and transmit these traits to their offspring. Finally, over multiple generations, the trait frequency shifts, resulting in population adaptation.

Step-by-Step Solution

Identify the initial genetic state of the population.

Random genetic variations exist prior to environmental selection.

Darwinian natural selection requires pre-existing variation upon which selection acts.

Analyze the impact of reproductive capacity.

Overproduction of offspring creates a struggle for existence.

Organisms produce more offspring than available environmental resources can support.

Apply the environmental selective pressure.

Exposure to the antibiotic results in differential survival.

Selective pressure eliminates susceptible organisms while favoring individuals with adapted variations.

Trace the transmission of advantageous traits.

Surviving resistant bacteria reproduce and pass beneficial traits to their progeny.

Differential reproduction ensures that favorable inherited traits increase in frequency.

Evaluate the evolutionary outcome at the population level.

The entire bacterial population becomes predominantly resistant over generations.

Evolution is defined as a cumulative change in allele/trait frequencies in a population over time.

Key Concept

Darwin's Theory of Natural Selection (Logical Sequence)

Question 46Question →

In a large, isolated population of a plant species, a catastrophic flood randomly eliminates over $95\%$ of the individuals regardless of their phenotypic traits. The few surviving individuals repopulate the area, resulting in allele frequencies in the restored population that differ significantly from those of the original gene pool. According to modern evolutionary theory (Neo-Darwinism), which mechanism is primarily responsible for this shift in allele frequencies?

Genetic drift via the bottleneck effect, where random sampling changes allele frequencies in small surviving populations.

Directional natural selection, where environmental stress favors specific advantageous survival phenotypes.

Environmentally induced mutation, where flood stress directly induced new beneficial alleles in the survivors.

Gene flow, where foreign alleles were introduced into the gene pool by immigrating individuals.

Show answer & explanation

Answer: Genetic drift via the bottleneck effect, where random sampling changes allele frequencies in small surviving populations.

Answer

Genetic drift via the bottleneck effect, where random sampling changes allele frequencies in small surviving populations.

The correct answer correctly identifies genetic drift through the bottleneck effect. When a population undergoes an unselective, catastrophic reduction in size, the small surviving subgroup represents an arbitrary random sample of the original gene pool. As this subgroup reproduces, the resulting allele frequencies differ randomly from the original population, which is a classic demonstration of genetic drift in modern evolutionary biology.

Step-by-Step Solution

Analyze the nature of the environmental event described in the stem.

The catastrophe affects individuals randomly without regard to their fitness or phenotypic traits.

This excludes natural selection, which requires differential reproductive success based on adaptive traits.

Evaluate the evolutionary impact of drastic population reduction.

A severe reduction in population size leaves a small sample of alleles (a genetic bottleneck).

In small populations, chance events cause substantial random fluctuations in allele frequencies independent of selective advantage.

Identify the modern evolutionary mechanism that corresponds to random sampling shifts in small populations.

Genetic drift operating through a population bottleneck.

Neo-Darwinism defines genetic drift as stochastic changes in gene frequency, particularly pronounced following bottleneck events.

Key Concept

Genetic Drift and Bottleneck Effect in Modern Evolutionary Synthesis

Question 47Question →

A botanist repeatedly prunes a species of shrub over its lifetime, causing it to develop a compact, stunted growth form. When seeds harvested from this pruned shrub are grown under normal, unpruned conditions, all offspring develop into full-sized plants of standard height. Which of the following conclusions best refutes Lamarck's theory of evolution based on this result?

Acquired somatic modifications resulting from environmental manipulation are not transferred to gametes or inherited by offspring.

Environmental stress directly induces genetic mutations that suppress growth only when pruning is actively maintained.

Disuse of growth hormones during pruning causes permanent organ atrophy that is counteracted by natural selection in the offspring.

Natural selection favors full-sized phenotypes only when soil nutrients exceed the threshold required for stunted growth.

Show answer & explanation

Answer: Acquired somatic modifications resulting from environmental manipulation are not transferred to gametes or inherited by offspring.

Answer

Acquired somatic modifications resulting from environmental manipulation are not transferred to gametes or inherited by offspring.

Lamarck's theory of evolution proposed that organisms pass on physical features acquired during their lifetime to their offspring (inheritance of acquired characteristics). The experiment demonstrates that pruning—an environmentally induced somatic change—does not alter the genetic code in the plant's reproductive cells (germline). Consequently, the offspring inherit the unedited genetic instructions for normal growth, refuting Lamarck's proposed mechanism.

Step-by-Step Solution

Identify the key postulate of Lamarck's Theory of Evolution being tested.

Lamarck's theory relies on the inheritance of acquired characteristics (somatic changes developed during an organism's life are passed to offspring).

Understanding Lamarck's mechanism is essential to evaluating why empirical evidence refutes it.

Analyze the experimental observations.

The parent plant acquired a stunted phenotype due to artificial pruning (environmental intervention), but its offspring produced from seed grew to normal height.

This shows that bodily changes (somatic cells) caused by environmental factors do not alter reproductive cells (germ cells).

Deduce the biological principle that invalidates the Lamarckian claim.

Phenotypic changes in somatic tissues are not encoded in DNA within germline cells, thereby proving acquired characteristics cannot be inherited.

Modern genetics and Weismann's germplasm concept confirm that only germline mutations/variations are transmitted across generations.

Key Concept

Inheritance of Acquired Characteristics vs. Somatic and Germline Differentiation

Estimated Time:1m 30s

Question 48Question →

A professional athlete undergoes years of intensive physical conditioning, resulting in significantly enlarged skeletal muscles and increased lung capacity. Based on the fundamental postulates of Lamarck's theory of evolution, which of the following outcomes would be predicted for this athlete's offspring?

They would naturally inherit larger muscles and increased lung capacity at birth without needing to undergo physical conditioning.

They would only develop larger muscles if environmental pressures in their generation make physical strength advantageous for survival.

They would inherit normal baseline physical traits because modifications acquired in somatic tissues during a parent's life cannot alter germ cells.

They would possess specific genetic mutations in their gametes induced directly by the physical strain of exercise.

Show answer & explanation

Answer: They would naturally inherit larger muscles and increased lung capacity at birth without needing to undergo physical conditioning.

Answer

The offspring would naturally inherit larger muscles and increased lung capacity at birth without needing physical conditioning.

The correct option accurately reflects Lamarck's postulate of the 'Inheritance of Acquired Characteristics.' Jean-Baptiste Lamarck proposed that structural modifications acquired by an organism through frequent organ use or environmental response during its lifetime are directly transmitted to its offspring.

Step-by-Step Solution

Identify the core principle of Lamarckism being tested in the scenario.

Lamarck's theory is built on two primary tenets: the Law of Use and Disuse, and the Law of Inheritance of Acquired Characteristics.

Understanding Lamarckian principles allows us to predict how acquired physical adaptations are thought to pass to offspring under his framework.

Apply the Law of Inheritance of Acquired Characteristics to the athlete's muscular development.

According to Lamarck, physical changes (enlarged muscles, increased lung capacity) gained by an individual during their lifetime through use are directly passed down to their offspring.

Lamarck believed that modifications in somatic organs directly influence the structural characteristics born into the next generation.

Key Concept

Inheritance of Acquired Characteristics

Question 49Question →

Arrange the following biological events in the correct chronological sequence to illustrate how a beneficial trait spreads in a population according to modern evolutionary theory.

Drag items to arrange them in the correct order

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Answer

The correct evolutionary sequence begins with a spontaneous gene mutation introducing a new allele, followed by natural selection favoring individuals with the advantageous trait, leading to differential transmission of the allele to offspring, and culminating in a shift in the population's overall allele frequency.

The correct sequence starts with the generation of novel genetic variation via random mutation. Natural selection then acts on this variation by favoring organisms with the advantageous phenotype. These individuals reproduce more successfully, transmitting the allele to their progeny. Over generations, this differential reproduction alters the overall allele frequency of the population's gene pool.

Step-by-Step Solution

Identify the origin of new genetic variation.

A random DNA mutation creates a novel allele in the gene pool.

Modern evolutionary theory establishes gene mutation as the primary source of novel genetic material.

Apply natural selection to the individual phenotypic trait.

Individuals possessing the beneficial allele demonstrate greater fitness.

Advantageous variations increase an organism's chances of surviving and reproducing.

Trace the inheritance of the trait into the next generation.

The favorable allele is passed to a greater proportion of offspring.

Differential reproduction naturally increases the representation of fit alleles in subsequent generations.

Determine the population-level genetic outcome.

The overall allele frequency in the gene pool changes over time.

Evolution in modern synthesis is measured by shifts in gene pool allele frequencies across generations.

Key Concept

Sequential mechanism of microevolution through mutation and natural selection

Estimated Time:45s

Question 50Question →

Immunological serological tests demonstrate high precipitin cross-reactivity when human antibodies are mixed with chimpanzee serum proteins, indicating close structural homology resulting from a recent common evolutionary ancestor. Is this statement True or False?

True

False

Show answer & explanation

Answer: True

Answer

True

The statement is true because comparative serology utilizes antigen-antibody reactions to quantify biochemical similarity. High precipitin formation between human anti-serum and chimpanzee serum proteins demonstrates that their plasma proteins share extremely similar amino acid sequences, providing strong molecular evidence for a recent common ancestor.

Step-by-Step Solution

Analyze the principle of comparative serology in evolutionary biochemistry.

Serum proteins (such as albumin and globulins) evolve through gene mutations over long periods. Closely related species share highly similar protein structures.

Fewer structural protein differences accumulate when organisms share a recent common ancestor.

Evaluate the mechanism of the precipitin test in cross-reactivity.

Antibodies produced against human serum proteins bind specifically to homologous protein epitopes in chimpanzee serum, causing high precipitation.

Antigen-antibody binding affinity increases with protein structural similarity.

Determine the validity of the statement based on biochemical evidence.

High cross-reactivity confirms a high degree of biochemical homology and recent shared ancestry.

The statement accurately describes the biochemical evidence for primate evolution.

Key Concept

Comparative serology and immunological cross-reactivity as evidence for evolutionary relationships

Question 51Question →

Match each core Lamarckian evolutionary postulate or related historical criticism on the left with its accurate biological mechanism or empirical evaluation on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Principle of Use and Disuse pairs with organ hypertrophy or atrophy from functional demand; Inheritance of Acquired Characteristics pairs with direct transmission of somatic changes to offspring; Internal Vital Impulse pairs with the proposed innate drive for complexity from non-living matter; Weismann's Germplasm Barrier pairs with the experimental refutation showing somatic changes do not affect germ line genetics.

Each concept correctly aligns with its historical and biological definition: Use and Disuse describes organ changes within a lifespan; Inheritance of Acquired Characteristics describes the proposed transfer of those changes to offspring; Internal Vital Impulse accounts for the drive toward complexity; and Weismann's Germplasm Barrier provides the classical empirical refutation distinguishing germline inheritance from somatic changes.

Step-by-Step Solution

Analyze the primary tenets of Lamarckism

Identify Use and Disuse as somatic modification during life, Inheritance of Acquired Traits as intergenerational transfer of those modifications, and Vital Impulse as the inherent drive for complexity.

Lamarck's theory relies on these distinct physiological and evolutionary mechanisms.

Evaluate historical scientific critiques of Lamarckian mechanisms

Recognize Weismann's experiment as establishing the barrier between germline (hereditary) and soma (body) cells.

Modern genetics refutes Lamarckism because somatic adaptations do not alter gametic DNA.

Match each postulate and critique to its corresponding definition

Connect left item 1 to right item 3, left item 2 to right item 4, left item 3 to right item 1, and left item 4 to right item 2.

Ensures precise conceptual mapping based on evolutionary biological definitions.

Key Concept

Lamarckian Postulates and Historical Refutation

Question 52Question →

Analogous structures, such as the camera-type eye of an octopus and the eye of a mammal, share a common embryonic origin and basic structural arrangement inherited from a shared recent ancestor.

True

False

Show answer & explanation

Answer: False

Answer

False. Analogous structures perform similar functions due to convergent evolution but do not share a common embryonic origin or ancestral structure.

The correct answer is False because analogous structures evolve independently to perform similar functions in response to similar environmental demands (convergent evolution), without sharing a common embryonic origin or recent ancestral structure.

Step-by-Step Solution

Define the biological concepts of homology and analogy in comparative anatomy.

Homologous structures share a common ancestry and embryonic development regardless of function, whereas analogous structures serve similar functions in different organisms due to environmental pressures but differ in embryonic origin.

Establishing accurate definitions is necessary to evaluate statements regarding evolutionary evidence.

Examine the specific anatomical structures presented (octopus eye vs. mammal eye).

Although both eyes perform the function of forming focused images, they develop from distinct embryonic layers (molluscan skin invagination vs. vertebrate neural tube outgrowth) and display key structural differences, such as the orientation of retinal photoreceptors.

Demonstrates that functional similarity in these organs is the result of convergent evolution rather than shared lineage.

Determine the truth value of the stem statement.

The statement incorrectly attributes shared embryonic origin and common ancestry to analogous structures.

Because analogous structures do not share a common embryonic origin or ancestral structure, the statement is false.

Key Concept

Distinction between homologous and analogous structures in comparative anatomy

Question 53Question →

The wing of a bird and the wing of a butterfly both enable flight, yet they possess completely different internal anatomies and embryonic origins. Which evolutionary term best describes these structures?

Analogous structures

Homologous structures

Vestigial organs

Atavistic structures

Show answer & explanation

Answer: Analogous structures

Answer

Analogous structures

The correct option is the one identifying these as analogous structures. Analogous structures perform similar biological functions—such as flight—in different species, but evolved independently in response to similar environmental challenges rather than from a common ancestor.

Step-by-Step Solution

Analyze the functional relationship between the bird wing and the butterfly wing.

Both structures serve the primary function of powered flight.

Identifying shared function helps determine if structures show convergent or divergent evolutionary pathways.

Examine the anatomical design and developmental origin of both organs.

Bird wings contain an endoskeleton composed of bones, whereas butterfly wings consist of chitinous membranes supported by veins.

Different embryonic origins indicate that the structures did not arise from a shared common ancestor.

Classify the structures according to evolutionary comparative anatomy.

Structures that perform similar functions but have distinct evolutionary and developmental origins are classified as analogous structures.

Analogous structures illustrate convergent evolution resulting from similar selection pressures.

Key Concept

Analogous vs. Homologous Structures

Question 54Question →

Match each evolutionary concept in modern evolutionary theory (Neo-Darwinism) to its corresponding genetic description or effect.

Click a left item, then click its matching right item

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Answer

Gene mutation matches with being the primary source of new genetic variations; Natural selection matches with driving non-random differential reproductive success; Gene pool matches with comprising the total sum of all genes and alleles; Genetic drift matches with causing random changes in allele frequencies in small populations.

In modern evolutionary theory (Neo-Darwinism), gene mutations supply new genetic variation; natural selection non-randomly increases adaptive allele frequencies; the gene pool represents all existing population alleles; and genetic drift causes random frequency changes, especially in small isolated groups.

Step-by-Step Solution

Identify the origin of new genetic diversity.

Gene mutation is recognized as the ultimate source of novel alleles.

Mutations introduce new genetic changes into the DNA of organisms.

Identify the mechanism that acts selectively on beneficial phenotypes.

Natural selection leads to differential reproductive success based on fitness.

Organisms best adapted to their environment pass on advantageous traits to offspring.

Define the collective genetic material of a population.

The gene pool consists of all alleles present across all individuals in the population.

Evolution in modern synthesis is defined as changes in allele frequencies within this gene pool.

Identify the mechanism of random, chance-based genetic frequency changes.

Genetic drift produces random fluctuations in allele frequencies, most notably in small populations.

Chance events rather than environmental adaptation govern genetic drift.

Key Concept

Mechanisms of Modern Evolutionary Synthesis and Population Genetics

Question 55Question →

In comparative serology, a higher degree of precipitation resulting from a reaction between human antiserum and the blood serum of another mammal indicates a more distant evolutionary relationship to humans.

True

False

Show answer & explanation

Answer: False

Answer

False. A higher degree of precipitation in comparative serology indicates greater molecular similarity and therefore a closer evolutionary relationship.

The statement is false. In comparative serology, human antiserum produces the greatest amount of precipitate when mixed with serum from closely related primates (such as chimpanzees) because their serum proteins are nearly identical in structure to human serum proteins. The amount of precipitate decreases as the evolutionary distance between the species increases.

Step-by-Step Solution

Recall the biochemical principles behind comparative serological testing.

Antibodies produced against human serum proteins bind to homologous serum proteins present in other species, forming an insoluble precipitate.

Organisms that share a recent common ancestor possess proteins with similar amino acid sequences and antigenic determinants.

Relate the amount of precipitate to evolutionary similarity.

A larger volume of precipitate indicates a higher percentage of shared protein structures and greater immunological cross-reactivity.

More matching epitopes allow more antibody-antigen complexes to form and precipitate out of solution.

Evaluate the claim made in the statement.

The statement incorrectly claims that higher precipitation corresponds to a more distant evolutionary relationship.

Higher precipitation directly correlates with closer evolutionary kinship, making the statement false.

Key Concept

Comparative Serology as Evidence for Evolution

Estimated Time:1m 0s

Question 56Question →

According to modern evolutionary theory, which statement correctly describes the primary contribution of sexual reproduction to genetic variation within a population?

It reshuffles existing alleles into unique combinations through crossing over and independent assortment.

It directly synthesizes entirely new alleles by modifying nucleotide sequences in somatic cells.

It allows phenotypic traits acquired through environmental exposure to be inherited by offspring.

It transforms continuous variations into fixed, discontinuous genetic categories across generations.

Show answer & explanation

Answer: It reshuffles existing alleles into unique combinations through crossing over and independent assortment.

Answer

Sexual reproduction reshuffles existing alleles into unique combinations through crossing over and independent assortment.

In modern evolutionary theory (Neo-Darwinism), sexual reproduction contributes to genetic diversity mainly by shuffling existing alleles during meiosis (crossing over and independent assortment) and random fertilization. This creates new genotypic combinations without generating brand-new genetic alleles.

Step-by-Step Solution

Distinguish between sources of new alleles and sources of genetic recombination.

Gene mutations are the ultimate source of novel alleles, whereas sexual reproduction rearranges existing alleles.

Modern synthesis clearly separates mutation (creation of new genetic material) from recombination (shuffling of existing alleles).

Identify the key mechanisms of genetic variation during sexual reproduction.

Processes such as crossing over during meiosis, independent assortment of chromosomes, and random fertilization generate new genotype combinations.

These mechanisms create unique offspring phenotypes without altering the fundamental genetic code of individual alleles.

Key Concept

Role of Sexual Reproduction and Recombination in Modern Evolutionary Theory

Question 57Question →

Match each microevolutionary genetic phenomenon on the left with its corresponding population genetics mechanism or outcome on the right.

Click a left item, then click its matching right item

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Answer

The phenomenon of retaining a deleterious recessive allele corresponds to balancing selection via heterozygote advantage. Stochastic allele frequency shifts after population reduction correspond to genetic drift via the bottleneck effect. Bimodal distribution of traits corresponds to disruptive selection. The movement of individuals reducing divergence between populations corresponds to gene flow via migration.

The retention of deleterious alleles occurs through balancing selection because heterozygous carriers gain a survival advantage (e.g., malaria resistance in sickle-cell heterozygotes). Sudden random allele changes following a drastic population drop constitute genetic drift operating through the bottleneck effect. Selection favoring both extreme phenotypes while penalizing intermediate forms defines disruptive selection. The exchange of genetic material between distinct populations through migration defines gene flow.

Step-by-Step Solution

Analyze the retention of lethal recessive alleles in a population.

Identify that when heterozygous individuals possess higher fitness than either homozygous form, the recessive allele is preserved in the population (balancing selection / heterozygote superiority).

This explains why negative selection against homozygotes fails to eliminate harmful recessive alleles.

Examine random frequency changes due to catastrophic size reduction.

Map non-selective population drop to sampling error and random allele loss/fixation known as genetic drift (bottleneck effect).

When population size drops precipitously, survival is stochastic rather than fitness-based.

Evaluate the mechanism generating a bimodal phenotypic distribution.

Pair selective pressure against intermediate phenotypes with disruptive selection.

Disruptive selection acts against average phenotypes, favoring both extreme tail traits.

Determine the effect of inter-population movement of individuals.

Connect movement of gametes or breeding individuals between populations to gene flow.

Gene flow introduces new alleles and homogenizes gene pools across geographic regions.

Key Concept

Mechanisms of Microevolution and Population Genetics

Estimated Time:2m 0s

Question 58Question →

In comparative biochemistry, the degree of evolutionary relationship between different organisms can be determined by comparing the amino acid sequences of conserved proteins such as Cytochrome c. If human Cytochrome c differs by $0$ amino acids from chimpanzees, $1$ amino acid from rhesus monkeys, $12$ amino acids from horses, and $45$ amino acids from baker's yeast, which of the following conclusions is most valid?

Humans share the most recent common ancestor with chimpanzees and the most distant common ancestor with baker's yeast.

Baker's yeast evolved directly into horses and primates through the inheritance of acquired physiological adaptations.

The structural similarities in Cytochrome c among these organisms are analogous features resulting from convergent evolution in identical habitats.

The variations in amino acid sequences represent discontinuous morphological variations caused entirely by environmental fluctuations.

Show answer & explanation

Answer: Humans share the most recent common ancestor with chimpanzees and the most distant common ancestor with baker's yeast.

Answer

Humans share the most recent common ancestor with chimpanzees and the most distant common ancestor with baker's yeast.

The correct answer correctly interprets comparative biochemical evidence. The fewer the differences in the amino acid sequence of a universal, conserved protein such as Cytochrome c between two species, the more recently those species diverged from a common ancestor. Since human and chimpanzee Cytochrome c sequences are identical, they share the most recent common ancestor, while the large difference of 45 amino acids between humans and yeast indicates a very ancient divergence.

Step-by-Step Solution

Analyze the quantitative biochemical data provided in the stem.

Sequence difference count from humans: Chimpanzee = 0, Rhesus monkey = 1, Horse = 12, Baker's yeast = 45.

Fewer amino acid differences indicate less time elapsed since divergence from a shared ancestor.

Relate sequence similarity to evolutionary distance.

Humans are most closely related to chimpanzees (0 differences) and most distantly related to baker's yeast (45 differences).

Homologous proteins mutate at a relatively constant rate over geological time; lower divergence reflects a more recent common ancestor.

Key Concept

Comparative Biochemistry as Evidence for Evolution

Estimated Time:1m 0s

Question 59Question →

Arrange the evolutionary events representing the process of adaptive radiation following ecological colonization in the correct sequential order from earliest to latest:

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Answer

The correct evolutionary sequence is: Colonization by an ancestral founder species -> Rapid population expansion and competition -> Ecological divergence into distinct niches -> Development of reproductive isolation leading to speciation.

Adaptive radiation begins with colonization, where a single founder species enters a new environment with minimal competition. As the population grows, competition for resources forces subpopulations to exploit unexploited ecological niches. Natural selection drives morphological divergence to optimize efficiency within these distinct roles. Finally, reproductive isolation arises between ecological specialists, preventing interbreeding and securing the formation of multiple distinct species.

Step-by-Step Solution

Identify the initial colonization event

Colonization of an isolated ecosystem by a founder species starts the process.

Adaptive radiation requires an ancestral population to colonize a new environment with unoccupied ecological niches.

Identify the ecological driver of diversification

Population expansion leads to intraspecific resource competition.

Increased population density generates competition, driving individuals to exploit alternative microhabitats and food sources.

Determine morphological and behavioral adaptation

Natural selection favors specialized traits adapted to distinct ecological niches.

Subpopulations exposed to different selective pressures undergo character displacement and ecological specialization.

Identify the final speciation step

Reproductive isolation barriers arise between divergent groups.

Speciation is finalized when gene flow between specialized lineages ceases due to prezygotic or postzygotic reproductive barriers.

Key Concept

Sequential Stages of Adaptive Radiation

Question 60Question →

The rapid diversification of a single ancestral species into multiple distinct species, each adapted to occupy a different ecological niche as seen in Galápagos finches, is known as which evolutionary process?

Adaptive radiation

Convergent evolution

Inheritance of acquired characteristics

Protective mimicry

Show answer & explanation

Answer: Adaptive radiation

Answer

Adaptive radiation

Adaptive radiation refers to the evolutionary process by which a single ancestral species diversifies into many different species, each occupying a distinct ecological niche and possessing specific adaptive features such as specialized beak shapes.

Step-by-Step Solution

Analyze the scenario described in the question stem.

The stem describes one ancestral species diversifying into multiple new species with specialized adaptations for different niches.

Identifying the pattern of evolutionary divergence from a single common ancestor is necessary to determine the correct concept.

Relate the evolutionary pattern to the correct term.

The process is adaptive radiation.

Adaptive radiation specifically describes the ecological diversification of a common ancestral line into distinct specialized species.

Key Concept

Adaptive radiation

Estimated Time:45s

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