- A population of bacteria has variation in antibiotic resistance: some are resistant (R) and some are not resistant (N). An antibiotic is added to the environment. The table shows the number of bacteria after 24 hours.
Start: R = 10, N = 990
After antibiotic: R = 800, N = 5
Which explanation best describes natural selection in this population using the evidence? (Natural selection affects populations, not individuals.)
Answer: Resistant bacteria survived and reproduced more in the presence of the antibiotic, so resistance became much more common in the population.
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 antibiotic resistance in bacteria, where resistant individuals survive and multiply in the presence of the antibiotic. The evidence from the table shows a dramatic shift, with resistant bacteria increasing from 1% to over 99% after 24 hours, due to their higher reproduction. To check understanding, compare starting and ending numbers to see if the advantageous trait dominates. A common misconception is that antibiotics cause bacteria to become resistant individually, but selection amplifies pre-existing resistance. In general, natural selection shifts trait frequencies toward those that enhance survival. Over generations, this can lead to widespread resistance in bacterial populations.
- A population of insects varies in body color: green and brown. In a forest, a disease kills many insects, but it does not affect survival differently for green vs. brown insects. The table shows trait frequencies before and after the disease.
Before disease: 50% green, 50% brown
After disease: 49% green, 51% brown (population size greatly reduced)
Which statement about natural selection is supported by this evidence? (Natural selection affects populations, not individuals.)
Answer: Because survival did not differ by color, the small change in percentages is more consistent with chance (genetic drift) than with selection on color.
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, but in this case, the disease did not favor green or brown insect colors differently, leading to no selective shift. The evidence from the table shows only a minor change from 50% to 51% brown, consistent with random genetic drift rather than selection. To check understanding, assess if survival differences by trait exist; if not, selection is not at work. A common misconception is that any population change means selection occurred, but drift can cause shifts without trait-based advantages. In general, natural selection shifts trait frequencies only when traits affect fitness. Over generations, distinguishing selection from drift helps explain evolutionary patterns.
- 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.)
Answer: Large beaks became more common because birds with large beaks produced more surviving chicks when hard seeds were common.
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.
- A bird population has variation in beak depth: shallow, medium, or deep. A drought leaves mostly large, hard seeds available for several years.
Researchers measured the percentage of each beak type:
Generation 0: shallow 40%, medium 45%, deep 15%
Generation 4: shallow 10%, medium 35%, deep 55%
Which statement about trait distribution is supported by the data and natural selection? (Natural selection affects populations, not individuals.)
Answer: Birds with deeper beaks likely had higher survival or produced more offspring when hard seeds were common, so deep beaks increased in the population over generations.
This question assesses understanding of how natural selection affects trait distribution when environmental conditions change. Natural selection acts on the variation already present in the bird population - shallow, medium, and deep beaks existed before the drought. The evidence shows that when hard seeds became the main food source during the drought, the population shifted from having mostly shallow and medium beaks to having mostly deep beaks (55%) after four generations. To verify the correct answer, identify which statement explains that birds with deeper beaks had advantages (better survival or more offspring) when hard seeds were common, leading to an increase in that trait over generations. A key misconception is thinking individuals develop new traits they need (option A) - instead, individuals with helpful traits that already exist leave more offspring. Natural selection shifts populations toward traits that provide advantages in the current environment, changing the proportion of different traits over multiple generations.
- In a population of beetles, there is variation in shell color: some are light green and some are dark green. After a wildfire, the ground becomes much darker. Researchers counted beetles before the wildfire and again 3 generations later.
Data: Before wildfire: 80 light, 20 dark. After 3 generations: 30 light, 70 dark.
Which explanation best describes how natural selection changed the trait distribution in this population? (Remember: natural selection affects populations, not individuals.)
Answer: Because the ground became darker, dark green beetles were more likely to survive and reproduce than light green beetles, so the dark color became more common over generations in the population.
This question tests understanding of how natural selection changes trait distributions in populations over time. Natural selection acts on existing variation in a population - in this case, some beetles were already light green and some were already dark green before the wildfire. The evidence shows that after the wildfire darkened the ground, the population shifted from mostly light beetles (80%) to mostly dark beetles (70%) over three generations. To check your answer, look for the explanation that describes differential survival and reproduction: dark beetles were more likely to survive on the dark ground, so they produced more offspring, causing the dark trait to become more common. A common misconception is that individuals change their traits in response to the environment (option A), but natural selection works by some individuals with certain traits surviving and reproducing more than others. Natural selection causes populations to shift toward traits that increase survival and reproduction in the current environment, changing the frequency of traits across generations.
- A population of mice shows variation in fur thickness: thin fur and thick fur. A colder-than-usual winter lasts for several years.
Data collected:
- Generation 1 offspring per adult (average): thin fur = 1.2, thick fur = 2.8
- Trait distribution:
- Start of study: 55% thin fur, 45% thick fur
- After 4 generations: 20% thin fur, 80% thick fur
Which statement about trait distribution is supported by the evidence? (Natural selection affects populations, not individuals.)
Answer: Thick-fur mice had higher reproduction in the cold, so the thick-fur trait became more common in the population over generations.
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 thin and thick fur in mice, favoring those that enhance survival and reproduction in colder conditions. The evidence shows population change through higher reproduction rates for thick-fur mice (2.8 offspring per adult versus 1.2), resulting in the trait distribution shifting from 45% to 80% thick fur over four generations. To check understanding, examine the average offspring per trait and verify if the population percentages change in favor of the trait with higher reproductive success. A common misconception is that individuals can grow new traits like thicker fur in response to the environment and pass them on, but natural selection works on heritable variations already present. In general, natural selection shifts trait frequencies by promoting traits that lead to more offspring in specific environments. Over generations, this adapts populations to challenges like cold winters without any individual effort or choice.
- A fish population has variation in body color (silver vs. speckled). Two lakes have different environments:
- Lake A has clear water and few plants.
- Lake B has murky water and many plants.
In both lakes, predators hunt visually.
After 5 generations, researchers measured trait frequencies.
Which comparison of outcomes is supported by the evidence? (Natural selection affects populations, not individuals.)
Answer: Different environments favored different existing color variants, leading to different trait distributions in the two populations over generations.
This question examines how different environments lead to different selection pressures and outcomes in separate populations. Natural selection acts on the pre-existing color variation in both fish populations - some fish are silver while others are speckled. The evidence demonstrates that different environments favor different color variants: in clear water (Lake A), one color provides better camouflage, while in murky water with plants (Lake B), the other color is advantageous. To analyze this correctly, recognize that the same trait can have different fitness values in different environments. A common misconception is that environments create new traits (option B) - the color variants already existed before selection occurred. Natural selection causes different trait distributions to evolve in the two lakes because predators have differential success catching fish based on visibility, leading each population to shift toward the color that provides better camouflage in its specific environment over multiple generations.
- 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.)
Answer: High-nectar flowers produced more seeds, so the high-nectar trait increased in frequency in the population over generations.
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.
- A student reads the following data about a snail population with variation in shell banding (banded vs. unbanded). Birds eat more visible snails on light-colored rocks.
Over 4 generations, the proportion of unbanded snails increased.
Which statement about trait distribution is supported by the evidence? (Natural selection affects populations, not individuals.)
Answer: Unbanded snails likely survived and reproduced more on light rocks, so the unbanded trait increased in frequency across generations.
This question tests interpretation of evidence for natural selection based on predation pressure. Natural selection acts on the existing shell pattern variation in the snail population - some snails have banded shells while others are unbanded. The evidence suggests that on light-colored rocks, unbanded snails are less visible to bird predators, giving them a survival advantage over more conspicuous banded snails. To evaluate the options correctly, look for explanations based on differential survival and reproduction rather than individual change or aesthetic preferences. A common misconception is that individuals can remove their traits to avoid predation (option A) - snails cannot remove their shell bands. Through natural selection, unbanded snails survive predation better on light rocks and therefore reproduce more successfully, causing the unbanded trait to increase in frequency across generations as their offspring make up a larger portion of the population.
- 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.)
Answer: The pesticide caused each insect to develop resistance during its lifetime, and then those insects passed that new resistance to their offspring.
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.
- A student looks at data from a population of lizards that vary in toe-pad size: small pads and large pads. After several unusually rainy years, more surfaces are slippery. The table shows survival to adulthood.
Small pads: 30 out of 100 juveniles survived
Large pads: 65 out of 100 juveniles survived
Which claim about natural selection is incorrect based on the data? (Natural selection affects populations, not individuals.)
Answer: Individual lizards with small pads can grow larger toe pads during their lifetimes in response to rain, and then pass those changed pads to offspring.
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 small and large toe pads in the lizard population, favoring large pads for better grip in rainy, slippery conditions. The evidence from the table shows higher survival for large-pad juveniles (65% vs. 30%), which could lead to increased frequency of large pads in the population. To check understanding, evaluate claims against data to identify which misalign with population-level changes. A common misconception is that individuals acquire and pass on traits like growing larger pads, but selection relies on inherited variation. In general, natural selection shifts trait frequencies by differential success of existing variants. Over generations, this drives evolutionary changes in populations without individual transformation.
- 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.)
Answer: Fast rabbits had higher reproductive success in the fox environment, so genes related to faster speed became more common in the population over generations.
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.
- 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.)
Answer: 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.
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.
- 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.)
Answer: The different environments favored different existing shell traits through differential survival and reproduction, so trait frequencies changed over generations in each population.
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.
- A population of lizards shows variation in leg length (short vs. long). A storm destroys many low bushes, leaving mostly tall shrubs. Lizards with longer legs can climb tall shrubs more easily to find food and mates.
Trait frequencies were measured over time.
Which prediction about future generations is supported by the data and the environmental condition? (Natural selection affects populations, not individuals.)
Answer: If tall shrubs remain common, long-leg lizards will likely become a larger proportion of the population over additional generations because they reproduce more.
This question assesses ability to make predictions about future trait distributions based on current selection pressures. Natural selection acts on the existing variation in leg length within the lizard population - some lizards have longer legs while others have shorter legs. The evidence shows that after the storm destroyed low bushes, long-legged lizards had better access to food and mates in the tall shrubs, leading to higher reproductive success. To make accurate predictions, consider how continued differential reproduction will affect future generations. A major misconception is that individuals can change their traits during their lifetime (option B) - short-legged lizards cannot grow longer legs. If the environmental conditions remain stable with mostly tall shrubs, natural selection will continue to favor long-legged lizards, causing them to leave more offspring and become an increasingly larger proportion of the population over additional generations.
- A population of fish shows variation in coloration: striped and solid. A new predator is introduced that more easily catches solid-colored fish in this habitat. The table shows the number of offspring produced by surviving adults.
Striped adults: average 30 offspring per adult
Solid adults: average 12 offspring per adult
Which statement about trait distribution is supported by the evidence over multiple generations? (Natural selection affects populations, not individuals.)
Answer: Striped fish will likely become more common in the population because they leave more offspring than solid fish in this environment.
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 striped and solid coloration in fish, favoring striped for better camouflage against the new predator. The evidence from the table shows striped fish producing more than twice as many offspring (30 vs. 12), predicting an increase in striped frequency. To check understanding, link offspring numbers to expected population changes over time. A common misconception is that individuals change colors to adapt, but selection depends on inherited traits. In general, natural selection shifts trait frequencies toward advantageous variants. Over generations, this enhances population survival in predator-rich environments.
- In a population of beetles, there is trait variation in shell color: light tan and dark brown. A bird predator hunts by sight on dark soil after a wildfire. The table shows the number of adult beetles that survived to reproduce each year.
Table (Adults that survived to reproduce):
Year 0: Light 50, Dark 50
Year 1: Light 18, Dark 42
Year 2: Light 10, Dark 45
Year 3: Light 6, Dark 47
Which explanation best describes how natural selection changed the trait distribution in this population over generations? (Remember: natural selection affects populations, not individuals.)
Answer: Because birds could see light beetles more easily on dark soil, dark beetles survived and reproduced more, so the population became mostly dark over generations.
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 shell colors in the beetle population, favoring those that provide a survival advantage in the changed environment. The evidence from the table shows a shift in population composition, with dark beetles increasing from 50% to about 89% by year 3, indicating higher survival and reproduction rates for dark beetles on the dark soil. To check understanding, compare the survival numbers across years and identify if the trait linked to better camouflage correlates with increased frequency. A common misconception is that individuals change their traits during their lifetime, like light beetles turning dark, but natural selection operates on populations through differential reproduction. In general, natural selection shifts trait frequencies by allowing individuals with advantageous traits to pass them on more successfully. Over multiple generations, this leads to adaptations that better suit the population to its environment.
- A population of rabbits varies in fur thickness: thin and thick. A colder climate lasts for many winters. The table shows the percent of rabbits with thick fur over time.
Year 1: 30% thick
Year 5: 45% thick
Year 10: 70% thick
Which prediction about future generations is supported by the data if the climate stays cold? (Natural selection affects populations, not individuals.)
Answer: The percent of thick-fur rabbits will likely continue to increase because thick fur is linked to higher survival and reproduction in cold conditions.
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 thin and thick fur in rabbits, favoring thick fur for better insulation in a persistently cold climate. The evidence from the table shows thick fur increasing from 30% to 70% over 10 years, supporting continued rise if conditions persist. To check understanding, extrapolate the trend and predict future percentages based on ongoing selection pressure. A common misconception is that all individuals change, like growing thicker fur, but selection works through differential reproduction. In general, natural selection shifts trait frequencies to match environmental demands. Over generations, this adapts populations to sustained changes like climate shifts.
- 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.)
Answer: More dark beetles survived and reproduced on dark soil, so the frequency of dark shells increased in the population over generations.
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.
- 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.)
Answer: 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.
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.
