Middle School Science Quiz: Natural Selection Effects
20 questions · exam conditions
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Natural Selection EffectsQuestion 1 of 20

A student writes: "After a drought, the plants evolved deeper roots so they could reach water." The class collected data from a plant population that varies in root depth: shallow vs. deep. During drought years, plants with deep roots produced an average of 60 seeds each, while shallow-root plants produced an average of 10 seeds each. Over 5 generations, the percent of deep-root plants increased from 40% to 75%.

Which claim about natural selection is incorrect in the student's statement when compared to the evidence? (Natural selection affects populations, not individuals.)

The student is incorrect because it suggests individual plants changed their roots because they needed water, instead of describing changes in trait frequency in the population over generations.
The student is correct because any drought automatically makes all plants develop deeper roots in the same generation.
The student is incorrect because natural selection cannot act on reproduction; it only acts on survival.
The student is correct because the data prove that deep roots are always the best trait in every environment.
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Middle School Science Quiz

Middle School Science Quiz: Natural Selection Effects

Practice Natural Selection Effects in Middle School Science 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 Natural Selection Effects, giving you a quick way to practice the rules, question types, and explanations that matter most for Middle School Science.

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

A student writes: "After a drought, the plants evolved deeper roots so they could reach water." The class collected data from a plant population that varies in root depth: shallow vs. deep. During drought years, plants with deep roots produced an average of 60 seeds each, while shallow-root plants produced an average of 10 seeds each. Over 5 generations, the percent of deep-root plants increased from 40% to 75%.

Which claim about natural selection is incorrect in the student's statement when compared to the evidence? (Natural selection affects populations, not individuals.)

  1. The student is incorrect because it suggests individual plants changed their roots because they needed water, instead of describing changes in trait frequency in the population over generations. (correct answer)
  2. The student is correct because any drought automatically makes all plants develop deeper roots in the same generation.
  3. The student is incorrect because natural selection cannot act on reproduction; it only acts on survival.
  4. The student is correct because the data prove that deep roots are always the best trait in every environment.
Explanation: Natural selection is the process by which certain traits become more or less common in a population over generations due to differences in survival and reproduction. Natural selection acts on existing variation in traits, such as shallow and deep roots in plants, favoring deep roots for better water access during droughts. The evidence shows deep-root plants increasing from 40% to 75% over five generations due to higher seed production (60 vs. 10). To check understanding, evaluate statements against data to see if they describe population shifts or individual changes. A common misconception is that organisms evolve traits out of need, but selection requires heritable variation. In general, natural selection shifts trait frequencies through differential success. Over generations, this refines populations without purposeful individual adaptation.

Question 2

In a population of beetles, there is trait variation in shell color (light vs. dark). A new predator hunts by sight on dark soil after a wildfire. Population counts over three generations are shown below.

Which explanation best describes how natural selection changed the trait distribution in this population? (Remember: natural selection affects populations, not individuals.)

  1. The wildfire created new dark-shell traits in individual beetles so they could survive better on the dark soil.
  2. More dark beetles survived and reproduced on dark soil, so the frequency of dark shells increased in the population over generations. (correct answer)
  3. Individual light beetles changed their shell color to dark during their lifetimes, so the population became darker.
  4. Because dark beetles are the strongest, they will always survive best in any environment, so dark shells increased everywhere.
Explanation: This question tests understanding of how natural selection changes trait distributions in populations over time. Natural selection acts on existing variation in traits - in this case, the beetles already had both light and dark shell colors before the environmental change. The evidence shows that after the wildfire created dark soil, dark beetles survived better because they were less visible to predators, allowing them to reproduce more successfully. To check your answer, look for the explanation that describes differential survival and reproduction leading to population change over generations, not individual beetles changing. A common misconception is that organisms can change their traits during their lifetime in response to environmental needs (like option C suggests). Natural selection works by shifting the frequency of existing traits in a population - those individuals with advantageous traits leave more offspring, causing that trait to become more common over multiple generations.

Question 3

A population of wildflowers varies in stem height: short (S) and tall (T). In a windy area, many tall stems break before making seeds. The table shows the average number of seeds produced per plant type.

Short plants: 120 seeds per plant Tall plants: 40 seeds per plant

Which evidence shows selection at work in this population over generations? (Natural selection affects populations, not individuals.)

  1. Short plants produce more seeds in the windy environment, so the proportion of short plants is expected to increase in later generations. (correct answer)
  2. Tall plants will become short during their lifetimes because wind forces them to adapt.
  3. All plants will be equally successful because natural selection only changes traits within a single generation.
  4. Stem height does not need to vary for natural selection to happen; wind will make the whole population short at once.
Explanation: Natural selection is the process by which certain traits become more or less common in a population over generations due to differences in survival and reproduction. Natural selection acts on existing variation in traits, such as short and tall stem heights in the wildflower population, favoring shorter stems that are less likely to break in windy conditions. The evidence from the table shows that short plants produce three times more seeds than tall ones, indicating a potential increase in short plant frequency over time. To check understanding, calculate the reproductive difference and predict how it would alter population composition in future generations. A common misconception is that individuals adapt by changing their traits, like tall plants becoming short, but selection affects populations through heredity. In general, natural selection shifts trait frequencies toward those conferring higher fitness. Over generations, this enhances the population's overall adaptation to environmental pressures.

Question 4

A population of mice shows variation in fur color (tan vs. white). The mice live on sand dunes. Over several generations, a disease reduces the number of white mice that survive to reproduce.

Data collected each generation are shown below.

Which statement about trait distribution is supported by the evidence? (Natural selection affects populations, not individuals.)

  1. The disease caused individual white mice to turn tan so they could avoid getting sick.
  2. Because white fur is a worse trait, natural selection always removes it from populations over time.
  3. White mice had lower survival and reproduction, so the proportion of tan fur increased in the population across generations. (correct answer)
  4. The population adapted in one generation because all mice needed to be tan to survive on sand dunes.
Explanation: This question examines how natural selection affects trait distribution when environmental factors reduce survival of certain variants. Natural selection operates on the variation already present in the mouse population - some mice have tan fur while others have white fur. The evidence demonstrates that when a disease disproportionately affects white mice, they have lower survival and reproduction rates compared to tan mice. To verify the correct answer, identify which option describes population-level change through differential reproduction rather than individual change. A key misconception is thinking that traits are inherently "good" or "bad" - white fur isn't universally worse, it just happens to be disadvantageous in this specific environment with this disease. Through natural selection, the reduced reproduction of white mice causes the proportion of tan fur to increase in the population across generations, shifting the overall trait distribution.

Question 5

A plant population shows variation in stem height (short vs. tall). In a crowded field, taller plants get more sunlight and produce more seeds.

Seed production data are shown below.

Which claim about natural selection is incorrect based on the evidence? (Natural selection affects populations, not individuals.)

  1. Taller plants produced more seeds, so the next generation had a higher proportion of tall stems in the population.
  2. Because tall stems had higher reproduction, the trait distribution can shift over generations in this environment.
  3. Short plants stretched to become tall because they needed sunlight, and this acquired height was inherited by their offspring. (correct answer)
  4. Variation in stem height mattered because the environment affected which plants left more offspring.
Explanation: This question requires identifying an incorrect claim about natural selection in plant populations. Natural selection operates on the existing variation in stem height - some plants are naturally tall while others are short. The evidence shows that in a crowded field, taller plants receive more sunlight and consequently produce more seeds, giving them a reproductive advantage. To find the incorrect claim, look for statements that violate the principle that acquired traits cannot be inherited. The misconception in option C is classic Lamarckism - the idea that organisms can change their traits through use or need and pass these changes to offspring. Natural selection actually works through differential reproduction; tall plants produce more seeds, so their offspring make up a larger proportion of the next generation, gradually shifting the population's trait distribution toward taller stems over multiple generations.

Question 6

A population of field mice shows variation in fur color: light gray and dark gray. The habitat changes from mostly light sand to mostly dark volcanic rock. The graph shows the percent of the population that is dark gray over 6 generations.

Generation 0: 50% dark Generation 1: 62% dark Generation 2: 70% dark Generation 3: 78% dark Generation 4: 84% dark Generation 5: 88% dark

Which statement about trait distribution is supported by this evidence? (Natural selection affects populations, not individuals.)

  1. Individual mice became darker because they needed better camouflage on the volcanic rock.
  2. The environment created new dark-fur traits in the mice after the habitat changed.
  3. Dark gray mice likely survived and reproduced more on the dark rock, increasing the frequency of dark fur in the population over generations. (correct answer)
  4. Natural selection happened because the mice chose to have dark fur to avoid predators.
Explanation: Natural selection is the process by which certain traits become more or less common in a population over generations due to differences in survival and reproduction. Natural selection acts on existing variation in traits, such as the light and dark gray fur colors in the mouse population, favoring those that provide better camouflage in the new dark volcanic rock habitat. The evidence from the graph shows a population change, with dark gray fur increasing from 50% to 88% over six generations, reflecting higher survival and reproduction of dark mice. To check understanding, track the percentage increase and link it to the environmental change that made dark fur advantageous. A common misconception is that the environment directly creates new traits, but variation must already exist for selection to act. In general, natural selection shifts trait frequencies by promoting the inheritance of beneficial traits. Over generations, this results in populations better adapted to their surroundings.

Question 7

In a population of beetles, there is trait variation in shell color: light green and dark green. A drought turns the habitat from leafy green to mostly brown soil. Birds hunt beetles by sight.

Population data:

  • Generation 0: 60% light green, 40% dark green
  • Of beetles that survived to reproduce in Generation 0: 30% light green, 70% dark green
  • Generation 2: 25% light green, 75% dark green

Which explanation best describes how natural selection influenced trait distribution in this population? (Remember: natural selection affects populations over generations, not individuals.)

  1. The drought created new dark-green shell genes in beetles because the environment needed them to match the brown soil.
  2. Dark-green beetles were more likely to survive bird predation on brown soil and reproduce, so the population's percent of dark-green beetles increased over generations. (correct answer)
  3. Individual light-green beetles turned dark green during the drought so they could survive, and then they passed that change to their offspring.
  4. Natural selection always makes a species stronger, so the beetle population became dark green to become a better species.
Explanation: Natural selection is the process where certain traits become more or less common in a population over generations due to differences in survival and reproduction. Natural selection acts on existing variation in traits, such as the light-green and dark-green shell colors in the beetle population, favoring those that provide a survival advantage in the changed environment. The evidence shows population change through data indicating that dark-green beetles had higher survival rates during the drought, leading to an increase in their proportion from 40% to 75% over generations. To check understanding, compare the survival rates of each trait and see if the population's trait distribution shifts accordingly in the data. A common misconception is that individuals change their traits during their lifetime and pass them on, but natural selection does not alter individuals; it selects among existing variations. In general, natural selection shifts trait frequencies by increasing the prevalence of advantageous traits through higher reproductive success. Over multiple generations, this results in populations becoming better adapted to their environments without any directed purpose or improvement toward a 'better' species.

Question 8

A population of insects includes two wing types: wide wings and narrow wings. A stormy season becomes common. Wide wings help insects glide longer, but narrow wings help them maneuver in strong gusts.

Evidence:

  • In calm years, wide-wing insects produce an average of 30 offspring; narrow-wing insects produce 20.
  • In stormy years, wide-wing insects produce an average of 12 offspring; narrow-wing insects produce 28.
  • The last 6 years have been stormy.

Which explanation best describes how natural selection is likely affecting the population now? (Natural selection affects populations, not individuals.)

  1. The insects will choose to grow narrower wings because they can sense the storms and decide to change.
  2. The storms will create a brand-new wing type in the next generation, so past variation is not important.
  3. Wide wings will always become more common because they are the strongest wing type in any environment.
  4. Narrow wings will likely become more common because insects with narrow wings have higher reproductive success in stormy years. (correct answer)
Explanation: Natural selection is the process where certain traits become more or less common in a population over generations due to differences in survival and reproduction. Natural selection acts on existing variation in traits, such as wide and narrow wings in insects, favoring narrow wings for maneuvering in stormy conditions. The evidence shows population change potential with narrow-wing insects producing more offspring (28 versus 12) in stormy years over the last six years. To check understanding, compare reproductive success in the current environment and predict which trait will increase based on ongoing conditions. A common misconception is that organisms choose to change traits like wing shape in response to sensing weather, but natural selection relies on heritable variations. In general, natural selection shifts trait frequencies by amplifying traits with reproductive advantages in prevailing environments. Over generations, this adapts populations to recurring challenges like frequent storms.

Question 9

A population of birds shows variation in beak size: small beaks and large beaks. A drought causes mostly hard, large seeds to be available for several years.

Data:

  • Generation 0: 70% small beaks, 30% large beaks
  • During the drought, average surviving chicks per pair: small beaks = 0.8, large beaks = 2.1
  • Generation 4: 35% small beaks, 65% large beaks

Which statement about trait distribution is supported by the evidence? (Natural selection affects populations, not individuals.)

  1. Large beaks became more common because birds with large beaks produced more surviving chicks when hard seeds were common. (correct answer)
  2. Birds with small beaks tried harder to crack seeds, so their beaks grew larger and the change was inherited.
  3. The drought directly changed the DNA of every bird so that all birds in the next generation had large beaks.
  4. Because the model uses percentages, it cannot be evidence; only the names of traits matter for natural selection.
Explanation: Natural selection is the process where certain traits become more or less common in a population over generations due to differences in survival and reproduction. Natural selection acts on existing variation in traits, such as small and large beaks in birds, favoring large beaks for cracking hard seeds during droughts. The evidence shows population change with large-beaked birds having more surviving chicks (2.1 versus 0.8), increasing from 30% to 65% large beaks over four generations. To check understanding, verify if the trait with higher chick survival rises in population percentage, aligning with the data trends. A common misconception is that individuals enlarge their beaks through effort and pass it on, but natural selection selects from genetic variations without individual changes. In general, natural selection shifts trait frequencies by promoting traits that enhance reproduction in resource-limited conditions. Over generations, this adapts populations to challenges like seed scarcity during droughts.

Question 10

A population of fish has variation in body color: silver and dark. A factory increases water pollution, making the water darker and reducing visibility.

Data:

  • Before pollution: 65% silver, 35% dark
  • During pollution, survival to reproduction (per 100 fish): silver = 30, dark = 70
  • After 4 generations: 30% silver, 70% dark

Which claim about natural selection is incorrect based on the data? (Natural selection affects populations, not individuals.)

  1. The darker water changed which color fish were more likely to survive and reproduce, shifting the population over generations.
  2. The population's trait distribution changed because dark fish had higher survival to reproduction in the polluted environment.
  3. Silver fish developed darker color during their lifetimes to match the water, and that is why the population changed. (correct answer)
  4. Trait variation (silver and dark) existed in the population before the pollution, and that variation mattered for which fish reproduced.
Explanation: Natural selection is the process where certain traits become more or less common in a population over generations due to differences in survival and reproduction. Natural selection acts on existing variation in traits, such as silver and dark body colors in fish, favoring dark colors for camouflage in polluted, darker water. The evidence shows population change with dark fish having higher survival (70 versus 30 per 100), shifting from 35% to 70% dark over four generations. To check understanding, identify claims that incorrectly attribute changes to individual adaptations and confirm data supports selection on pre-existing variations. A common misconception is that individuals develop new colors during their lifetime to match the environment, but natural selection amplifies existing traits through differential reproduction. In general, natural selection shifts trait frequencies by increasing adaptive traits in response to environmental changes. Over generations, this results in populations better camouflaged in altered habitats like polluted waters.

Question 11

A population of flowering plants has variation in flower color: red and white. Bees visit red flowers more often in this area.

Data:

  • Average seeds produced per plant: red = 120 seeds, white = 40 seeds
  • Trait distribution:
    • Generation 0: 40% red, 60% white
    • Generation 3: 75% red, 25% white

Which prediction about future generations is supported by the data if bee preference stays the same? (Natural selection affects populations, not individuals.)

  1. The percent of red-flowered plants will likely continue to increase because red plants produce more seeds on average. (correct answer)
  2. Individual white-flowered plants will turn red during their lifetime so they can attract bees and survive.
  3. The environment will create red color in all plants immediately, so the next generation will be 100% red no matter what.
  4. Flower color does not need to vary for natural selection; bees will choose plants randomly and the distribution will stay 40% red forever.
Explanation: Natural selection is the process where certain traits become more or less common in a population over generations due to differences in survival and reproduction. Natural selection acts on existing variation in traits, such as red and white flower colors in plants, favoring red flowers that attract more bees for pollination. The evidence shows population change with red-flowered plants producing more seeds (120 versus 40), increasing from 40% to 75% red over three generations. To check understanding, predict future trends by seeing if the trait with higher seed production continues to rise in frequency if conditions persist. A common misconception is that individuals change color to attract pollinators during their life, but natural selection selects from heritable traits without individual adaptation. In general, natural selection shifts trait frequencies by increasing advantageous traits through greater reproductive output. Over generations, this adapts populations to factors like pollinator preferences.

Question 12

A student writes this claim about a population of fish that shows variation in body shape (slender vs. deep-bodied):

"When a new predator arrived, each fish adapted by becoming deeper-bodied so it could escape. That is why the population had more deep-bodied fish later."

Data collected over 6 years show that deep-bodied fish had higher survival to adulthood and produced more offspring than slender fish after the predator arrived, and the percent of deep-bodied fish increased from 30% to 68%.

Which part of the student's claim is unsupported by the evidence and is scientifically incorrect about natural selection affecting populations?

  1. The idea that deep-bodied fish became more common in the population over time.
  2. The idea that deep-bodied fish had higher survival and reproduction after the predator arrived.
  3. The idea that each individual fish changed its body shape because of the predator and then passed that change to offspring. (correct answer)
  4. The idea that an environmental change (a predator) can affect which traits are more successful in a population.
Explanation: This question evaluates the ability to identify misconceptions about natural selection by analyzing a student's claim against supporting evidence. Natural selection acts on existing variation in body shape (slender vs deep-bodied) in the fish population. The evidence supports that deep-bodied fish had higher survival and reproduction after the predator arrived, and that the population shifted from 30% to 68% deep-bodied over 6 years - this demonstrates natural selection through differential reproductive success. To find the incorrect part of the claim, identify statements that violate how natural selection actually works. The fundamental error in the student's claim is stating that "each fish adapted by becoming deeper-bodied" - this suggests individual fish changed their body shape during their lifetime, which is impossible. Natural selection works by shifting trait frequencies in populations over generations, not by individuals changing their inherited traits. The evidence supports ideas A, B, and D about population change, differential reproduction, and environmental effects on trait success, but contradicts idea C about individual change.

Question 13

A population of fish shows variation in body shape: slender and deep-bodied. In Lake A, a new predator can easily catch slender fish. In Lake B, there is no predator change. After 5 generations, scientists measure body-shape percentages.

Lake A: deep-bodied = 80%, slender = 20% Lake B: deep-bodied = 45%, slender = 55%

Which statement is supported by the comparison of outcomes? (Remember: natural selection affects populations, not individuals.)

  1. Fish in Lake A chose to become deep-bodied because they wanted to avoid predators, so most individuals changed shape.
  2. The predator in Lake A likely caused differential survival or reproduction that increased the frequency of deep-bodied fish in that population over generations, while Lake B did not experience the same selection pressure. (correct answer)
  3. Deep-bodied fish are always better in every habitat, so they increased in Lake A and should also increase in Lake B even without a predator.
  4. The results show that the environment directly creates the deep-bodied trait in Lake A fish after predators arrive.
Explanation: The core skill is comparing outcomes in different environments to understand natural selection's role in trait changes. Natural selection acts on variation, like slender and deep-bodied shapes already in the fish populations of both lakes. The data shows a higher percentage of deep-bodied fish in Lake A with predators, contrasted with Lake B, evidencing selection-driven population differences. A checking strategy is to contrast trait frequencies in environments with and without specific pressures. One misconception is that traits arise directly from the environment without variation, but selection amplifies existing advantageous traits. Over generations, selection increases frequencies of traits that enhance survival in specific conditions. This process generalizes how populations diverge based on local selection pressures.

Question 14

A population of insects has variation in pesticide resistance: resistant and non-resistant. A student makes these four claims after reading the data below.

Data: After pesticide use for 3 generations, the percent resistant increases from 10% to 65%.

Which claim about natural selection is incorrect? (Remember: natural selection affects populations, not individuals.)

  1. Natural selection changed the population because resistant insects survived and reproduced more often, increasing the frequency of resistance over generations.
  2. Resistance became more common because the pesticide killed more non-resistant insects before they could reproduce.
  3. The pesticide caused each insect to develop resistance during its lifetime, and then those insects passed that new resistance to their offspring. (correct answer)
  4. The data show a change in trait distribution over generations, which is consistent with natural selection acting on existing variation.
Explanation: The core skill is evaluating claims to identify incorrect ideas about natural selection's mechanisms. Natural selection acts on variation, with resistant and non-resistant insects already present before pesticide application. The data shows a rise in resistant insects over generations, evidencing a population shift through differential survival. To check claims, determine if they align with population-level changes or wrongly suggest individual adaptations. A misconception is that traits develop during an organism's life and are inherited, but selection filters existing variations. In general, selection boosts frequencies of beneficial traits across generations. This shift in trait distributions occurs without purposeful changes by individuals.

Question 15

A population of snails has variation in shell banding: banded and unbanded. In a grassy area, banded shells are easier for predators to spot. In a rocky area, unbanded shells are easier to spot. After 4 generations, scientists count shell types.

Grassy area: banded = 20%, unbanded = 80% Rocky area: banded = 75%, unbanded = 25%

Which explanation best describes natural selection in these populations using the evidence? (Remember: natural selection affects populations, not individuals.)

  1. Snails in each area changed their shell pattern during their lives to match the background, so the counts differ.
  2. The different environments favored different existing shell traits through differential survival and reproduction, so trait frequencies changed over generations in each population. (correct answer)
  3. Banded shells are more attractive, so they should increase in both places regardless of predators or habitat.
  4. The rocky and grassy habitats created the shell patterns directly, meaning snails did not need variation for natural selection to occur.
Explanation: The core skill is describing how natural selection leads to different trait outcomes in varied environments. Natural selection acts on variation, like banded and unbanded shells already present in the snail populations. The count data shows shifts toward unbanded in grassy areas and banded in rocky areas, evidencing environment-specific population changes. To check explanations, ensure they connect predation and camouflage to trait frequencies. A misconception is that traits change for attractiveness, but selection is driven by survival advantages. Over generations, favored traits increase in frequency based on local conditions. This process generalizes how selection shapes diverse trait distributions across populations.

Question 16

A population of mice shows variation in fur color: tan or gray. An owl hunts by sight in a rocky area.

In one year, researchers recorded survival to adulthood:

  • Tan: 20 survivors out of 100 born
  • Gray: 60 survivors out of 100 born

Three generations later, the population is 70% gray and 30% tan.

Which evidence best shows natural selection at work in this population? (Natural selection affects populations, not individuals.)

  1. Gray mice had higher survival to adulthood than tan mice, and the proportion of gray fur increased over generations. (correct answer)
  2. Some mice wanted to avoid being eaten, so they chose to grow gray fur during their lifetime.
  3. All mice in the rocky area became gray within one generation because the environment required it.
  4. Owls prefer to hunt tan mice because tan is a weaker color, so gray mice are always the best type everywhere.
Explanation: This question evaluates understanding of evidence for natural selection affecting populations. Natural selection acts on the existing variation in fur color - some mice were already tan and others were already gray before the owl predation. The evidence clearly shows differential survival: gray mice had much higher survival to adulthood (60%) compared to tan mice (20%) in the rocky environment where owls hunt by sight. To identify evidence of natural selection, look for data showing that one trait leads to better survival or reproduction than another, resulting in that trait becoming more common over generations. A common misconception is that individuals choose to change their traits (option B) or that changes happen instantly (option C), but natural selection works through differential survival and reproduction of existing variants. The population shifted from having both colors to being mostly gray (70%) after three generations because gray mice survived better and left more offspring in this environment.

Question 17

A population of rabbits has variation in running speed: slow, medium, and fast. A new predator (foxes) moves into the area. Researchers tracked the number of offspring produced per rabbit that survived to reproduce.

Average offspring per rabbit:

  • Slow: 1.2
  • Medium: 2.0
  • Fast: 3.1

After 5 generations, the percentage of fast rabbits increased.

Which explanation best describes natural selection in this population using the evidence? (Natural selection affects populations, not individuals.)

  1. Rabbits practiced running faster because they needed to escape foxes, so each rabbit became fast during its lifetime.
  2. Fast rabbits were morally better at surviving, so nature rewarded them by giving them more offspring.
  3. Fast rabbits had higher reproductive success in the fox environment, so genes related to faster speed became more common in the population over generations. (correct answer)
  4. The foxes created a new fast-speed trait in the rabbits, so fast rabbits appeared only after foxes arrived.
Explanation: This question assesses understanding of how natural selection changes populations based on reproductive success data. Natural selection acts on the existing variation in running speed among rabbits - slow, medium, and fast speeds were already present before foxes arrived. The evidence shows clear differences in reproductive success: fast rabbits produced the most offspring (3.1 average), followed by medium (2.0) and slow (1.2), indicating that faster rabbits had advantages in escaping foxes. To identify the correct explanation, look for one that connects higher reproductive success to changes in trait frequency over generations through genetic inheritance. Common misconceptions include thinking individuals change during their lifetime (option A) or that new traits are created by the environment (option D), but natural selection works by favoring individuals with beneficial traits who then pass their genes to more offspring. The population shifted toward having more fast rabbits because those individuals left more offspring, increasing the frequency of speed-related genes over five generations.

Question 18

A population of flowers has variation in nectar amount: low-nectar and high-nectar. In this area, a new pollinator arrives that visits high-nectar flowers more often.

Seed production per plant (average):

  • Low-nectar: 40 seeds
  • High-nectar: 90 seeds

After several generations, high-nectar flowers become more common.

Which statement about trait distribution is supported by the evidence? (Natural selection affects populations, not individuals.)

  1. High-nectar flowers produced more seeds, so the high-nectar trait increased in frequency in the population over generations. (correct answer)
  2. Low-nectar flowers decided to make more nectar because they wanted to attract pollinators.
  3. The new pollinator created the high-nectar trait in individual plants after it arrived.
  4. High nectar is always the best trait in any environment, so natural selection will always increase nectar amount no matter what pollinators are present.
Explanation: This question assesses understanding of how natural selection affects trait distribution through differential reproduction. Natural selection acts on the existing variation in nectar production - some flowers already produced low nectar and others high nectar before the new pollinator arrived. The evidence shows that high-nectar flowers produced many more seeds (90) compared to low-nectar flowers (40) because the new pollinator visited them more often, and high-nectar flowers became more common over several generations. To identify the supported statement, look for one that correctly links higher seed production to increased trait frequency without suggesting individual plants change or that traits are created by the environment. Common misconceptions include thinking individuals decide to change (option B) or that environments create new traits (option C), but natural selection works through differential reproductive success of existing variants. The population shifted toward more high-nectar flowers because those plants left more offspring through better pollination, increasing the frequency of high-nectar genes over generations.

Question 19

A student looks at these data from a fish population with variation in body color (silver or dark). After pollution makes the water murkier, researchers find that dark fish produce more offspring.

Data: Generation 1: 70% silver, 30% dark Generation 6: 35% silver, 65% dark

Student's explanation: "The fish adapted by turning dark because they needed to hide in murky water."

Which part of the student's explanation is an error based on natural selection? (Natural selection affects populations, not individuals.)

  1. It incorrectly says individual fish turned dark because they needed to; the data support that dark fish already present left more offspring, changing the population over generations. (correct answer)
  2. It is correct because natural selection happens when individuals change their traits during their lifetime in response to the environment.
  3. It is incorrect because natural selection only changes traits if every fish is identical at the start.
  4. It is incorrect because the population changed too slowly; natural selection must always change traits in a single generation.
Explanation: This question tests ability to identify errors in explanations of natural selection. Natural selection acts on variation that already exists - the fish population had both silver and dark individuals before the water became murky. The evidence shows the population shifted from mostly silver (70%) to mostly dark (65%) over six generations, with dark fish producing more offspring in murky water. To identify the error, recognize that the student incorrectly claims individual fish "turned dark because they needed to" - this represents the misconception that individuals change their traits during their lifetime in response to needs. The correct explanation is that dark fish already present in the population had better reproductive success in murky water, so their offspring made up a larger portion of later generations. Natural selection doesn't involve individuals changing themselves; it involves differential survival and reproduction of existing variants, causing population-level changes over multiple generations.

Question 20

A population of lizards shows variation in leg length: short or long. A storm removes many trees, leaving mostly open ground with fewer places to climb.

Researchers measured survival in the new environment:

  • Short legs: 50 survivors out of 200
  • Long legs: 120 survivors out of 200

After 4 generations, long-legged lizards make up 75% of the population.

Which prediction about future generations is supported if the environment stays mostly open ground? (Natural selection affects populations, not individuals.)

  1. More lizards will be born with long legs because the open ground environment favors long-legged lizards surviving and reproducing more. (correct answer)
  2. All individual short-legged lizards will grow longer legs during their lifetime to match the environment.
  3. Leg length will stop varying because natural selection requires no variation for traits to change.
  4. Long legs will become common in one generation because natural selection always works immediately.
Explanation: This question evaluates predictions about future population changes based on natural selection evidence. Natural selection acts on the existing variation in leg length - both short and long legs were present before the environmental change. The evidence shows that long-legged lizards had much better survival (120/200) compared to short-legged lizards (50/200) in the new open ground environment, and the population has already shifted to 75% long-legged after four generations. To make a valid prediction, consider that if the environment stays the same, the trait providing better survival will continue to increase in frequency through differential reproduction. A key misconception is thinking individuals will change their traits during their lifetime (option B) or that changes happen instantly (option D), when actually population changes occur gradually over generations. If the open ground environment persists, natural selection will continue favoring long-legged lizards who survive and reproduce more, causing that trait to become even more common in future generations.