IB Biology Quiz: Apply Natural Selection
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Apply Natural SelectionQuestion 1 of 18

In some fish species, two different male mating strategies exist. Large, dominant males defend territories to attract females. Small, 'sneaker' males mimic females to get close to the territories and fertilize eggs undetected. If the number of dominant males becomes too high, it is easier for sneaker males to succeed. If the number of sneaker males becomes too high, females and dominant males become better at detecting them.

This scenario, where the fitness of a phenotype depends on its frequency in the population, is an example of what evolutionary mechanism? [HL]

Genetic drift
Stabilizing selection
Negative frequency-dependent selection
Positive frequency-dependent selection
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IB Biology Quiz

IB Biology Quiz: Apply Natural Selection

Practice Apply Natural Selection 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 Apply Natural Selection, giving you a quick way to practice the rules, question types, and explanations that matter most for IB Biology.

How to use this quiz

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.

All questions

Question 1

In some fish species, two different male mating strategies exist. Large, dominant males defend territories to attract females. Small, 'sneaker' males mimic females to get close to the territories and fertilize eggs undetected. If the number of dominant males becomes too high, it is easier for sneaker males to succeed. If the number of sneaker males becomes too high, females and dominant males become better at detecting them.

This scenario, where the fitness of a phenotype depends on its frequency in the population, is an example of what evolutionary mechanism? [HL]

  1. Genetic drift
  2. Stabilizing selection
  3. Negative frequency-dependent selection (correct answer)
  4. Positive frequency-dependent selection
Explanation: The correct answer is C. Negative frequency-dependent selection occurs when the fitness of a phenotype decreases as it becomes more common. In this case, both the dominant and sneaker male strategies are successful when they are rare and less successful when they are common. This type of selection maintains genetic variation in the population by preventing any single strategy from becoming fixed. A is incorrect as this is a selective process, not a random one. B is incorrect as it favors an intermediate, not oscillating frequencies of different strategies. D is the opposite; it occurs when fitness increases as a phenotype becomes more common, which would lead to the fixation of one strategy.

Question 2

Cave-dwelling fish often have vestigial eyes that are small and non-functional. The ancestors of these fish lived in surface waters and had fully functional eyes. The underground cave environment is completely dark.

What is the most accepted evolutionary explanation for the loss of eye function in these cavefish?

  1. The lack of use caused the eyes to atrophy within each fish's lifetime, and this trait was inherited.
  2. Mutations for blindness occurred because the fish were in a dark environment and no longer needed eyes.
  3. The fish population is slowly evolving towards a new form of sight that does not require eyes.
  4. Maintaining functional eyes requires metabolic energy, so individuals with mutations causing eye reduction had higher fitness. (correct answer)
Explanation: The correct answer is C. This explanation relies on the principle of energy trade-offs. Developing and maintaining complex structures like eyes is metabolically expensive. In a completely dark environment where eyes provide no benefit, any random mutation that reduces eye development would free up energy for other functions like growth or reproduction. These individuals would have a slight fitness advantage and be selected for over time. A is a Lamarckian explanation. B is incorrect because mutations are random and are not directed by environmental needs. D is speculative and not supported by the principles of selection; evolution is not goal-directed.

Question 3

In a certain species of fish, populations in clear, shallow streams are subject to predation by birds from above. These populations show a high frequency of drab, camouflaged phenotypes. An adjacent population in a deep, murky lake has no avian predators but is preyed upon by larger fish that hunt by detecting movement. This second population has a high frequency of brightly coloured males.

What is the most plausible explanation for the difference in coloration between the two fish populations?

  1. The murky water in the lake caused mutations for bright colours, while the clear water caused mutations for drab colours.
  2. Gene flow between the populations has been prevented, leading to the random fixation of different colour alleles in each location.
  3. The different predation pressures in each environment have selected for different optimal phenotypes. (correct answer)
  4. The drab fish in the stream will eventually migrate to the lake to acquire bright colours for better mating success.
Explanation: The correct answer is C. This is a classic example of divergent selection. In the stream, predation from above selects for camouflage (drab colours). In the lake, the absence of this pressure and the presence of a different pressure (detection by movement) may allow sexual selection for bright colours (which can signal fitness to mates) to become the dominant selective force. A is incorrect as environmental conditions do not cause specific mutations. B suggests genetic drift is the sole cause, which is less likely than selection given the strong correlation between environment and phenotype. D incorrectly suggests that individuals can change their traits in response to a need and that migration is directed towards this goal.

Question 4

A bacterial population is exposed to an antibiotic. Most bacteria are killed, but some individuals with a resistance mutation survive. These survivors reproduce, and the next generation has a higher proportion of resistant bacteria. The same antibiotic is used again on this new generation.

What is the expected outcome of the second antibiotic application compared to the first?

  1. A higher percentage of the bacterial population will survive the second application. (correct answer)
  2. The antibiotic will cause new, more effective resistance mutations to appear.
  3. The antibiotic will be more effective, as the bacteria have been weakened by the first exposure.
  4. All surviving bacteria will lose their resistance as the selection pressure is reapplied.
Explanation: The correct answer is A. The first application of the antibiotic selected for resistant individuals. These individuals reproduced, passing the resistance allele to their offspring. Therefore, the second generation starts with a much higher frequency of the resistance allele than the original population, leading to a higher survival rate when the same antibiotic is reapplied. B is incorrect because antibiotics do not cause mutations. C is incorrect; the population is not 'weakened' but is instead 'stronger' in terms of resistance. D is the opposite of what natural selection would predict; the resistance allele is beneficial and will be selected for, not lost.

Question 5

A farmer has been using a specific chemical pesticide for 10 years to protect crops. Initially, the pesticide was highly effective. Now, the farmer observes that a much higher concentration of the pesticide is needed to achieve the same level of pest control.

What is the best evolutionary explanation for this observation?

  1. The pests have developed physiological tolerance within their lifetimes, a process known as acclimatization.
  2. The pesticide has caused mutations in the pests, making them stronger and more resistant over time.
  3. The pesticide has acted as a selective agent, favouring the reproduction of pre-existing resistant pests. (correct answer)
  4. The pests have changed their diet to avoid the crops that are sprayed with the pesticide.
Explanation: The correct answer is C. This is a classic example of natural selection for pesticide resistance. The original pest population had variation in susceptibility. The pesticide killed the susceptible individuals, leaving the resistant ones to survive and reproduce. Over generations, the frequency of resistance alleles in the population increased. A is incorrect because acclimatization is a non-heritable change within an individual's life, not an evolutionary change in a population. B incorrectly states that the pesticide caused the mutations for resistance. D describes a behavioural change, which is possible, but the need for a higher pesticide concentration points directly to increased physiological resistance in the pest population that still feeds on the crop.

Question 6

A new viral disease emerges and wipes out 99% of a cheetah population. The remaining 1% of cheetahs survive because they possess a rare, heritable trait that confers immunity. What is the most likely long-term consequence for the cheetah population if it recovers?

  1. The recovered population will have less genetic diversity than the original population. (correct answer)
  2. The recovered population will be phenotypically identical to the original population.
  3. The survivors will lose their immunity as the virus is no longer a threat.
  4. Each cheetah will individually acquire immunity and pass it to their offspring.
Explanation: The correct answer is A. This event is a population bottleneck, a type of genetic drift. Even though natural selection determined which individuals survived (the immune ones), the drastic reduction in population size means that a vast amount of genetic variation (alleles unrelated to immunity) is lost from the gene pool. The recovered population will be descended from a small number of founders, resulting in lower overall genetic diversity. B is incorrect because the allele frequencies (especially for immunity) will be drastically different. C is incorrect as the immunity is a heritable trait. D describes inheritance of acquired characteristics.

Question 7

The evolution of the horse involved a general trend over millions of years from small, forest-dwelling animals with multiple toes to large, plains-dwelling animals with a single hoof. This change was correlated with a shift in climate that replaced forests with grasslands.

What type of selection best explains this long-term trend in the horse lineage? [HL]

  1. Directional selection (correct answer)
  2. Stabilizing selection
  3. Disruptive selection
  4. Frequency-dependent selection
Explanation: The correct answer is A. Directional selection occurs when conditions favour individuals exhibiting one extreme of a phenotypic range, thereby shifting a population's frequency curve for the phenotypic character in one direction or the other. The consistent trend towards larger size and fewer toes in response to the changing environment (from forest to grassland) is a classic example of directional selection operating over a long evolutionary timescale. B, C, and D do not fit the described pattern of a consistent shift in one direction.

Question 8

In a process of domestication, humans selected for wolves that were less aggressive and more tolerant of human presence. Over many generations, this led to the evolution of the domestic dog, which exhibits many traits not seen in wolves, such as floppy ears and varied coat colours, a phenomenon known as domestication syndrome.

How does this process differ from natural selection? [HL]

  1. It involves heritable traits, whereas natural selection acts on non-heritable traits.
  2. The selective agent is human preference rather than environmental pressures. (correct answer)
  3. It occurs over a few years, while natural selection requires millions of years.
  4. It does not require pre-existing variation in the ancestral population.
Explanation: The correct answer is B. The key difference between artificial selection (domestication) and natural selection is the agent of selection. In natural selection, environmental factors (predation, climate, resource availability) determine which individuals are more likely to survive and reproduce. In artificial selection, humans determine which individuals reproduce based on desired traits. A is incorrect; both processes require heritable traits. C is an overgeneralization; while artificial selection is often faster, natural selection can also occur rapidly (e.g., antibiotic resistance). D is incorrect; both processes depend on pre-existing variation.

Question 9

A significant environmental change occurs, creating a new selection pressure on a population. Which of the following factors would most increase the likelihood that the population will adapt and not go extinct?

  1. A very small initial population size.
  2. A low mutation rate within the population.
  3. A long generation time for the species.
  4. A high degree of pre-existing genetic variation. (correct answer)
Explanation: The correct answer is C. Natural selection can only work with the raw material available. A population with high genetic variation is more likely to contain individuals who already possess alleles that are advantageous in the new environment. These individuals will survive and reproduce, allowing the population to adapt. A small population size (A) makes a population more vulnerable to extinction and genetic drift. A low mutation rate (B) reduces the input of new variation. A long generation time (D) slows down the rate at which natural selection can produce change.

Question 10

A population of insects feeds on a specific plant species. The plant evolves a new chemical toxin to which most insects are susceptible. However, a small percentage of the insect population possesses a pre-existing allele that confers resistance to the toxin. These resistant insects survive and reproduce, while susceptible insects die before reproducing.

Which statement accurately describes the role of the new plant toxin in the evolution of the insect population?

  1. The toxin caused the resistance allele to appear in the insect population through mutation.
  2. The toxin acted as a selective pressure, increasing the frequency of the pre-existing resistance allele. (correct answer)
  3. The toxin led to the development of resistance in individual insects, which was then inherited by their offspring.
  4. The toxin decreased the overall fitness of the insect population, preventing any future adaptation.
Explanation: The correct answer is B. Natural selection acts on existing variation. The plant toxin did not create the resistance allele; it only provided an environmental pressure that favored individuals already possessing it. This led to an increase in the allele's frequency over generations. A is incorrect because selection pressures do not cause specific mutations; mutations arise randomly. C describes a Lamarckian concept of inheritance of acquired characteristics, which is not the mechanism of natural selection. D is incorrect because while the toxin initially decreases fitness for many, the population is clearly adapting, as shown by the survival of resistant individuals.

Question 11

The average birth weight of human babies is around 3.5 kg. Babies that are significantly smaller or larger than this have historically had higher rates of mortality. Smaller babies are more susceptible to disease, while larger babies can cause complications during delivery.

This situation is an example of which type of natural selection? [HL]

  1. Disruptive selection, as it acts against the average individual.
  2. Directional selection, as it pushes the average birth weight higher.
  3. Stabilizing selection, as it favours the intermediate phenotype. (correct answer)
  4. Sexual selection, as birth weight is determined by mate choice.
Explanation: The correct answer is C. Stabilizing selection occurs when intermediate phenotypes have higher fitness than extreme phenotypes. In this case, babies with an average birth weight have the highest survival rates, so the selection pressures act to keep the population mean stable and select against the extremes (very small and very large babies). A is the opposite of the scenario. B would occur if, for example, only larger babies survived best. D is incorrect as mate choice is not the primary selective pressure on birth weight described.

Question 12

A large, genetically diverse population of snails lives on an island where the terrain consists of either very light-coloured rocks or very dark, volcanic soil, with no intermediate shades. Birds that prey on the snails hunt by sight. Which pattern of selection is most likely to act on the shell colour of these snails over time? [HL]

  1. Directional selection, favouring either light or dark shells, but not both.
  2. Stabilizing selection, favouring intermediate-coloured shells that blend in with both backgrounds.
  3. Disruptive selection, favouring both very light and very dark shells while selecting against intermediate shades. (correct answer)
  4. Artificial selection, as the birds are consciously choosing which snails to eat.
Explanation: The correct answer is C. The environment has two distinct niches where different extreme phenotypes are favoured. Snails with very light shells are camouflaged on the rocks, and snails with very dark shells are camouflaged on the soil. Intermediate-coloured snails would be poorly camouflaged in both environments and thus be preyed upon more heavily. This selection against the mean and for the extremes is the definition of disruptive selection. A is incorrect because both extremes are favored. B is incorrect because the intermediate phenotype is selected against. D is incorrect as the birds' hunting is a natural, not an artificial, selection pressure.

Question 13

A common misconception is that an organism can adapt to its environment during its lifetime. For example, a giraffe might stretch its neck to reach higher leaves. How does the modern theory of evolution by natural selection refute this idea?

  1. Natural selection acts on populations, not individuals, by favouring heritable traits that enhance reproductive success. (correct answer)
  2. Organisms cannot change their physical traits during their lifetime, even through effort.
  3. Adaptation is a completely random process and is not influenced by the environment.
  4. Giraffes with shorter necks are actually more fit, as they expend less energy.
Explanation: The correct answer is A. This addresses the core difference between Lamarckian evolution and Darwinian evolution. Natural selection operates on the level of the population over generations. An individual organism does not evolve. Instead, individuals with certain inherited traits are more likely to survive and reproduce than others, causing the frequencies of those traits to increase in the population over time. B is not entirely true (e.g., muscle development), but more importantly, such acquired traits are not heritable. C is incorrect; mutation is random, but selection is non-random. D is an unsupported claim and irrelevant to the mechanism.

Question 14

In many mammal species, males are significantly larger and have more elaborate features (e.g., antlers, manes) than females, despite these features potentially increasing predation risk. How does the theory of natural selection explain the evolution of these seemingly disadvantageous traits?

  1. These traits are a result of genetic drift, becoming fixed by chance in the population.
  2. These traits improve survival by allowing males to better defend the group against predators.
  3. These traits increase reproductive success by improving success in male-male competition or being attractive to females. (correct answer)
  4. These traits are acquired during a male's lifetime and passed on to his sons to demonstrate his strength.
Explanation: The correct answer is C. This describes sexual selection, which is a component of natural selection. Traits that increase an individual's reproductive success can be selected for even if they slightly decrease survival. In this case, success in competing for mates (intrasexual selection) or being chosen by mates (intersexual selection) outweighs the survival cost. A is incorrect because such widespread and complex traits are unlikely to be the result of random drift. B is a possible secondary benefit, but the primary driver for these sexually dimorphic traits is typically competition for mates. D describes the inheritance of acquired characteristics, a Lamarckian idea.

Question 15

A population of finches on an island primarily eats small, soft seeds. A severe, prolonged drought eliminates most plants that produce small seeds, leaving only plants that produce large, hard-shelled seeds. The finch population has natural variation in beak size.

What is the most likely immediate consequence for the finch population in the next generation?

  1. Most finches will develop larger, stronger beaks through increased use, and pass this trait to their offspring.
  2. The average beak size in the population will increase because individuals with larger beaks are more likely to survive and reproduce. (correct answer)
  3. The population will experience a high rate of mutation to produce larger beaks in response to the food source change.
  4. The entire finch population will likely go extinct as they are specialized for small seeds.
Explanation: The correct answer is B. The drought created a strong selective pressure. Finches that already had larger beaks (due to existing genetic variation) were better able to crack the available hard seeds, giving them a survival and reproductive advantage. This leads to an increase in the frequency of alleles for larger beaks in the next generation, thus increasing the average beak size. This is directional selection. A describes Lamarckian evolution. C is incorrect because mutations are random, not directed by environmental needs. D is possible, but given the stated variation in beak size, adaptation is a more likely outcome than immediate extinction.

Question 16

Which of the following is a necessary condition for natural selection to lead to evolutionary change in a population?

  1. The population must be in Hardy-Weinberg equilibrium.
  2. All individuals in the population must have the same level of fitness.
  3. The environment must remain stable and unchanging for many generations.
  4. There must be heritable variation for the trait being selected. (correct answer)
Explanation: The correct answer is D. Natural selection can only act on traits that have a genetic basis and can be passed on to offspring (heritable). Furthermore, there must be differences (variation) among individuals for selection to have an effect. Without heritable variation, any survival differences among individuals will not result in a change in the population's genetic makeup over time. A is incorrect; Hardy-Weinberg equilibrium describes a population that is not evolving. B is incorrect; variation in fitness is the very basis of natural selection. C is incorrect; environmental change is often the driving force of natural selection.

Question 17

Why is the concept of 'overproduction of offspring' a critical component of the theory of natural selection?

  1. It guarantees that some offspring will be phenotypically identical to their parents.
  2. It ensures that the population size increases exponentially without limit.
  3. It creates competition for limited resources, leading to differential survival and reproduction. (correct answer)
  4. It reduces the amount of genetic variation in the population in each generation.
Explanation: The correct answer is C. Thomas Malthus's principle, which Darwin applied to nature, states that organisms produce more offspring than can possibly survive given limited resources (food, space, etc.). This leads to a 'struggle for existence'. In this struggle, individuals with advantageous heritable traits are more likely to survive and reproduce, driving natural selection. A is incorrect; sexual reproduction ensures offspring are not identical. B is the opposite of what happens; competition limits population growth. D is incorrect; overproduction and sexual reproduction maintain or increase variation.

Question 18

In the context of evolution, what is the most accurate definition of 'biological fitness'?

  1. The ability of an individual to survive for the longest possible time.
  2. The measure of an individual's physical strength, speed, and overall health.
  3. The complexity of an organism's anatomical and physiological systems.
  4. The number of fertile offspring an individual produces that survive to reproduce. (correct answer)
Explanation: The correct answer is C. Biological or Darwinian fitness is a measure of reproductive success. It is not just about survival (A) or physical prowess (B), but about the contribution an individual makes to the gene pool of the next generation. An individual that survives a long time but has no offspring has a fitness of zero. An individual that produces many offspring that themselves go on to reproduce is considered highly fit. Complexity (D) is not a measure of fitness.