IB Biology Quiz: Understand Evolution And Speciation
20 questions · exam conditions
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Understand Evolution And SpeciationQuestion 1 of 20

In a certain plant, allele A for tall stems is dominant to allele a for short stems. A drought acts as a selection pressure, favouring short-stemmed plants which are less prone to wind damage and water loss. Which statement accurately describes how the population would evolve?

Individual tall plants will shrink to become short, passing this trait to their offspring.
The mutation rate from allele A to allele a will increase in response to the drought.
All tall plants (AA and Aa) will be eliminated from the population in a single generation.
The frequency of allele a will increase in the population's gene pool over generations.
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IB Biology Quiz

IB Biology Quiz: Understand Evolution And Speciation

Practice Understand Evolution And Speciation in IB Biology with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Understand Evolution And Speciation, giving you a quick way to practice the rules, question types, and explanations that matter most for IB Biology.

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Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

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Question 1

In a certain plant, allele A for tall stems is dominant to allele a for short stems. A drought acts as a selection pressure, favouring short-stemmed plants which are less prone to wind damage and water loss. Which statement accurately describes how the population would evolve?

  1. Individual tall plants will shrink to become short, passing this trait to their offspring.
  2. The mutation rate from allele A to allele a will increase in response to the drought.
  3. All tall plants (AA and Aa) will be eliminated from the population in a single generation.
  4. The frequency of allele a will increase in the population's gene pool over generations. (correct answer)
Explanation: Natural selection acts on populations, not individuals, by changing allele frequencies. In this scenario, short plants (aa) have higher fitness, so they are more likely to survive and reproduce. This means they will pass on more copies of the a allele to the next generation, increasing its frequency in the gene pool over time. Individual plants do not change their genetics (A), selection is gradual, not absolute (C), and selection does not cause mutations (D).

Question 2

In a species of plant, a mutation occurs resulting in tetraploidy (4n). These tetraploid plants can self-pollinate or mate with other tetraploid plants, but when they cross with the original diploid (2n) plants, the resulting triploid (3n) offspring are sterile.

Based on the information provided, what evolutionary process is being described?

  1. Allopatric speciation through geographical isolation.
  2. Sympatric speciation through a pre-zygotic reproductive barrier.
  3. Adaptive radiation into a new ecological niche.
  4. Sympatric speciation through a post-zygotic reproductive barrier. (correct answer)
Explanation: This is an example of sympatric speciation because it occurs within the same geographical area. The reproductive barrier is the formation of sterile triploid offspring. Since the zygote (the triploid offspring) is formed but is not fertile, this is a post-zygotic barrier. Polyploidy is a common mechanism for sympatric speciation in plants.

Question 3

The existence of many different species of finches on the Galápagos Islands, all originating from a single ancestral species, is a classic example of adaptive radiation. Which combination of factors is essential for this process to occur?

  1. A stable environment and a very high mutation rate in the ancestral population.
  2. Geographical isolation on different islands and the availability of diverse, unoccupied ecological niches. (correct answer)
  3. Convergent evolution with other bird species and strong competition from mainland birds.
  4. The absence of natural selection and a completely uniform food source across all islands.
Explanation: Adaptive radiation requires an opportunity for diversification. This is provided by geographical isolation (e.g., separate islands), which limits gene flow, and the presence of various unoccupied ecological niches (e.g., different food sources), which provides different selection pressures, driving the single ancestral species to evolve into multiple specialized species.

Question 4

The pentadactyl limb is found in amphibians, reptiles, birds, and mammals. It is adapted for different functions like walking, flying, and swimming. What is the most logical conclusion that can be drawn from the presence of this structure across these diverse groups?

  1. All these groups evolved from a common ancestor that possessed a pentadactyl limb. (correct answer)
  2. The pentadactyl limb is the optimal design for locomotion, so it evolved independently in each group.
  3. Flying, swimming, and walking exert identical selection pressures on limb development.
  4. The genes for the pentadactyl limb are highly prone to mutation, leading to diverse forms.
Explanation: The pentadactyl limb is a classic example of a homologous structure. Its presence in such diverse vertebrates, despite its modification for different functions, is strong evidence that they share a common ancestor that had this limb structure. This is an example of divergent evolution or adaptive radiation. It is highly improbable that such a complex structure would evolve independently multiple times (B).

Question 5

The fossil record provides evidence for evolution, but it is acknowledged to be incomplete. What is the most significant reason for this incompleteness?

  1. Many fossils are destroyed by human activities such as construction and mining.
  2. Soft-bodied organisms do not contain genes and therefore cannot evolve or leave evidence.
  3. Scientists have only been searching for fossils for a few hundred years, which is not enough time.
  4. The specific environmental conditions required for fossilization are rare, so most organisms never fossilize. (correct answer)
Explanation: Fossilization requires a very specific set of circumstances, such as rapid burial in sediment and an anaerobic environment, to prevent decomposition. The vast majority of organisms that have ever lived decomposed completely without leaving a trace. This makes the fossil record inherently incomplete. While other factors contribute, the rarity of the fossilization process itself is the most fundamental reason.

Question 6

A population of insects is sprayed with a new pesticide. Most of the insects die, but a few survive. These survivors reproduce, and over several generations, the population becomes resistant to the pesticide. What is the source of the initial resistance in the population?

  1. The pesticide caused beneficial mutations for resistance in the surviving insects.
  2. The insects that survived learned to avoid the pesticide and taught their offspring.
  3. Pre-existing genetic variation meant some insects already had an allele for resistance. (correct answer)
  4. The insects developed resistance through repeated exposure within their lifetimes.
Explanation: Natural selection acts on existing variation. The pesticide did not create resistance; it selected for it. Within the original population, there was random genetic variation, and a few individuals happened to possess alleles that conferred some degree of resistance. These individuals were the ones who survived and reproduced, passing those alleles on. The pesticide is a selection pressure, not a mutagenic agent in this context (A), and acquired characteristics are not inherited (B, D).

Question 7

A biologist proposes that a species of fish underwent speciation due to disruptive selection on jaw size, related to feeding on two different types of snails (small and large). What evidence would most strongly support this sympatric speciation hypothesis? [HL]

  1. Fossil evidence showing a gradual increase in average jaw size over time for the entire species.
  2. Genetic data showing frequent interbreeding and high gene flow between the small-jawed and large-jawed fish.
  3. Evidence that fish with intermediate jaw sizes are less successful at feeding on either snail type and have lower fitness. (correct answer)
  4. Discovery of a second fish species with a similar jaw morphology in a different, isolated lake.
Explanation: Disruptive selection is a key driver of sympatric speciation. It occurs when extreme phenotypes are favoured over intermediate ones. In this case, evidence that fish with intermediate jaws are at a disadvantage (lower fitness) would strongly support the hypothesis that selection is actively driving the population to diverge into two specialized forms within the same location. High gene flow (B) would prevent speciation. A gradual increase in average size (A) suggests directional, not disruptive, selection.

Question 8

A small group of finches is blown from the South American mainland to an isolated oceanic island. Which of the following is most likely to increase the rate of speciation in this new colony compared to the mainland population?

  1. The founder effect, resulting in a gene pool that is not representative of the original population. (correct answer)
  2. Increased gene flow with the large mainland population, introducing new alleles.
  3. A perfectly stable island environment with no variation in food sources or habitats.
  4. The absence of any mutation within the genomes of the colonizing finches.
Explanation: The founder effect occurs when a new population is established by a small number of individuals whose gene pool differs by chance from that of the source population. This genetic drift, combined with new selection pressures on the island, can accelerate genetic divergence and lead to rapid speciation. Increased gene flow (B) would inhibit speciation. A stable environment (C) would reduce selection pressures, and an absence of mutation (D) would remove the raw material for evolution.

Question 9

Industrial melanism in the peppered moth (Biston betularia) is a classic example of natural selection. In a polluted industrial area, the frequency of the dark-coloured (melanic) form increased. What was the most direct cause of this change?

  1. The pollution directly caused mutations that turned light-coloured moths dark.
  2. The dark-coloured moths had a higher reproductive rate regardless of the environment.
  3. Soot from factories darkened the tree trunks, giving camouflaged dark moths a survival advantage against predation. (correct answer)
  4. Light-coloured moths preferentially migrated away from polluted areas, leaving only dark moths behind.
Explanation: The change in the environment (soot-darkened trees) changed the selection pressure. Dark moths, which previously stood out, were now better camouflaged from bird predators, while light moths became more visible. This differential predation led to the increased survival and reproduction of the melanic form. Pollution did not directly cause the mutation (A), and the advantage was environment-dependent (B). Migration patterns (D) were not the primary mechanism.

Question 10

A fossil record of a marine invertebrate shows long periods of morphological stasis, interrupted by brief periods of rapid change where new species appear. Which model of evolution is best supported by this evidence?

  1. Phyletic gradualism, where change is slow and constant over time.
  2. Punctuated equilibrium, where change is concentrated in rapid speciation events. (correct answer)
  3. Convergent evolution, where unrelated species develop similar traits.
  4. Lamarckian evolution, where acquired characteristics are inherited.
Explanation: The pattern described—long periods of little to no change (stasis) followed by short bursts of rapid change and speciation—is the hallmark of the punctuated equilibrium model of evolution. Phyletic gradualism (A) would show slow, steady change. Convergent evolution (C) describes the pattern of trait development, not the tempo. Lamarckian evolution (D) is a discredited mechanism.

Question 11

For natural selection to lead to speciation, what must be true about the relationship between two diverging populations?

  1. Gene flow between the two populations must be significantly reduced or eliminated. (correct answer)
  2. One population must have a significantly higher mutation rate than the other.
  3. The two populations must be exposed to identical environmental conditions and predators.
  4. Both populations must increase in size exponentially without any limiting factors.
Explanation: Speciation requires the divergence of two populations into distinct evolutionary lineages. This cannot happen if there is substantial gene flow (interbreeding) between them, as gene flow acts to homogenize the gene pools. Therefore, a reduction or elimination of gene flow is a prerequisite for speciation, allowing different mutations and selection pressures to drive the populations apart genetically.

Question 12

Two species of frogs, Rana pipiens and Rana clamitans, live in the same ponds but do not interbreed because their mating calls have different frequencies. What is this an example of?

  1. A temporal pre-zygotic isolation mechanism.
  2. A behavioural pre-zygotic isolation mechanism. (correct answer)
  3. A gametic post-zygotic isolation mechanism.
  4. Hybrid inviability, a post-zygotic mechanism.
Explanation: The barrier to reproduction occurs before a zygote can be formed, so it is pre-zygotic. The specific barrier is related to courtship rituals (the mating call), which falls under behavioural isolation. Temporal isolation (A) relates to mating at different times. Post-zygotic mechanisms (C, D) occur after fertilization.

Question 13

Sharks (cartilaginous fish) and dolphins (mammals) both possess streamlined bodies and powerful tails for propulsion in an aquatic environment. What do these shared features exemplify?

  1. Homologous structures resulting from divergent evolution from a recent common ancestor.
  2. Analogous structures resulting from convergent evolution due to similar selection pressures. (correct answer)
  3. Vestigial structures that have lost their original function over evolutionary time.
  4. Adaptive radiation where one ancestral species diversifies to fill many different niches.
Explanation: Sharks and dolphins are not closely related, with one being a fish and the other a mammal. Their streamlined bodies are adaptations to the same environment (water) and the same selection pressures (need for efficient movement). Structures that have similar functions but different evolutionary origins are called analogous structures, and they arise through convergent evolution.

Question 14

How does the practice of selective breeding in agriculture and animal husbandry provide evidence for evolution by natural selection?

  1. It demonstrates that species are fixed and do not change over time, even with human intervention.
  2. It shows that artificial selection can cause rapid and significant changes in a species, suggesting that natural selection could do so over longer timescales. (correct answer)
  3. It proves that acquired characteristics, like a farmer's preference for large fruit, can be passed on to the next generation.
  4. It shows that all variations within a species are equally advantageous and can be selected for with equal success.
Explanation: Selective breeding (artificial selection) is a powerful analogy for natural selection. By showing that human-directed selection can cause dramatic changes in a species in a relatively short time, it supports the idea that undirected, environmental selection (natural selection) can cause even greater changes over geological time. It demonstrates the potential for populations to evolve, not that they are fixed (A). It operates on heritable variation, not acquired characteristics (C).

Question 15

What is the key distinction between allopatric and sympatric speciation? [HL]

  1. Allopatric speciation occurs rapidly, while sympatric speciation is a slow, gradual process.
  2. Allopatric speciation is driven by natural selection, while sympatric speciation is driven by genetic drift.
  3. Allopatric speciation only occurs in animals, while sympatric speciation only occurs in plants.
  4. Allopatric speciation involves a geographical barrier, while sympatric speciation does not. (correct answer)
Explanation: The defining difference lies in the mechanism that initiates the reduction in gene flow. In allopatric ('other country') speciation, this is a physical, geographical barrier that separates populations. In sympatric ('same country') speciation, a reproductive barrier emerges within a single, coexisting population, for example through polyploidy or disruptive selection.

Question 16

In the context of evolution, what is the significance of the universality of the genetic code across nearly all organisms?

  1. It suggests that convergent evolution is the primary mechanism for generating biodiversity.
  2. It provides strong evidence for a common ancestry for all life on Earth. (correct answer)
  3. It indicates that the genetic code is optimal and cannot be changed by mutation.
  4. It demonstrates that all organisms have the exact same number of genes in their genomes.
Explanation: The fact that the same codons specify the same amino acids in bacteria, plants, fungi, and animals is compelling evidence that this system was established early in the history of life and inherited by all subsequent lineages. This shared fundamental characteristic points to a common origin, or common ancestor. It does not relate to convergent evolution (A) and is not immutable (C), though changes are rare and often lethal. Organisms have vastly different numbers of genes (D).

Question 17

When a horse and a donkey mate, they produce a sterile offspring, the mule. How does this outcome fit into the concept of speciation?

  1. It shows that horses and donkeys are still the same species because they can produce offspring.
  2. It is an example of hybrid inviability, a pre-zygotic reproductive barrier.
  3. It is an example of hybrid sterility, a post-zygotic reproductive barrier confirming they are distinct species. (correct answer)
  4. It demonstrates that sympatric speciation is occurring between horse and donkey populations.
Explanation: The biological species concept defines species based on the ability to produce fertile offspring. Because the mule is sterile, the horse and donkey are confirmed as separate species. This reproductive barrier occurs after the formation of a zygote (the mule), making it a post-zygotic mechanism. Specifically, it is hybrid sterility.

Question 18

A population of flightless beetles is split into two geographically isolated groups by the formation of a river. For these two groups to become distinct species, which of the following must occur?

  1. The two groups must develop noticeable differences in colour or size.
  2. The two groups must encounter different selection pressures in their new environments.
  3. The two groups must accumulate enough genetic differences to prevent the production of fertile offspring. (correct answer)
  4. The river must remain as a permanent barrier for at least one million years.
Explanation: The biological species concept defines a species as a group of organisms that can interbreed to produce viable, fertile offspring. Speciation is complete when two populations can no longer do this. While different selection pressures (B) drive the genetic divergence, and morphological differences (A) may result, the ultimate criterion is reproductive isolation (C). A specific time frame (D) is not a defining requirement; the rate of speciation varies.

Question 19

Which of the following scenarios is an example of temporal isolation leading to reproductive isolation?

  1. Two species of birds that have different, elaborate mating dances.
  2. Two species of plants where the pollen of one cannot fertilize the ovule of the other.
  3. Two species of coral that release their gametes into the water on different nights based on moon phases. (correct answer)
  4. Two species of squirrels that are separated by a large, impassable river.
Explanation: Temporal isolation is a pre-zygotic barrier where two species reproduce at different times (time of day, season, or year). The coral species releasing gametes on different nights is a clear example of this. The bird dances are behavioural isolation (A), the plant pollen issue is gametic isolation (B), and the river is geographical isolation (D), which leads to allopatric speciation.

Question 20

Which statement best explains why evolution is considered a robust scientific theory?

  1. It is a well-supported guess that has not yet been disproven, but could be with new evidence.
  2. It has been proven to be an absolute fact that is no longer subject to any scientific debate or refinement.
  3. It is a comprehensive explanation for a wide range of observations from fossils, genetics, and anatomy that has withstood repeated testing. (correct answer)
  4. It is a belief system accepted by the majority of biologists to explain the origins of life on Earth.
Explanation: In science, a 'theory' is not a mere guess (A). It is a well-substantiated explanation of some aspect of the natural world that is based on a body of facts that have been repeatedly confirmed through observation and experiment. Evolution is supported by evidence from many different fields (C). Science does not deal in absolute proofs (B), and theories are always subject to refinement. It is an evidence-based framework, not a belief system (D).