1 question, one for each idea where we can. Answer them, then see which ideas to fix.
Question 1 of 1
Which statement about evolution in species living today is accurate?
Answer and reasoning
ASpecies that look like their ancient fossil relatives have stopped evolving altogether. A student who judges evolution by outward appearance picks this. A similar body form does not mean that DNA and allele frequencies have stopped changing.
BHumans have stopped evolving, because modern medicine allows nearly everyone to survive. A student who equates evolution with survival of the fittest picks this. Mutation, drift and migration still act on human populations, and people still differ in how many children they have.
CPopulations of living species keep evolving as allele frequencies change.Correct All species have evolved and continue to evolve: mutation, selection, drift and migration keep changing allele frequencies in every population, generation after generation.
DEvolution is too slow to be observed in any population within a human lifetime. A student who thinks evolution always takes millions of years picks this. Bacteria, insects and viruses have been observed evolving within years, for example in resistance to antibiotics and pesticides.
In preparation: 0 of 1 sections compiled and reviewed. The rest show key terms and common mistakes from our question bank until they are.
7.8.A.1 Continuing evolution Fix
Continuing evolution
All species have evolved and continue to evolve: in every population, allele frequencies keep changing from generation to generation through mutation, natural selection, genetic drift and migration.
Genomic change over time
Mutations accumulate in a lineage's DNA generation after generation. Comparing genomes sampled at different times, such as stored samples of laboratory populations or DNA from ancient remains, shows this change directly.
Continuous change in the fossil record
In many lineages, fossils from successive rock layers show a trait changing gradually through intermediate forms, and the living species continues the series.
Evolution of resistance
A population evolves resistance to an antibiotic, pesticide, herbicide or chemotherapy drug when the chemical kills susceptible individuals or cells while those with heritable resistance survive and reproduce, so resistance alleles become more common over generations. Resistance alleles arise by random mutation, not in response to the chemical.
Selection pressure
An environmental factor, such as a pesticide or a drug, that causes individuals with some heritable variants to survive and reproduce more than others.
Fitness cost of resistance
A disadvantage that a resistance allele can bring when the chemical is absent, such as slower growth or fewer offspring. Where there is a cost, the allele tends to decline once the chemical is no longer used.
Pathogen
An organism or virus that causes disease in its host. Pathogen populations are large and reproduce quickly, so they can evolve within months or years.
Emergent disease
A disease that has newly appeared in a population, or is rapidly increasing, often because a pathogen has evolved the ability to infect a new host species or to escape existing immunity.
Surface-protein change in a virus
Mutations change the proteins on a virus's surface. Variants whose proteins bind to new kinds of host cells, or are no longer recognized by the host's existing immunity, can spread, so the virus population changes over time.
Students often think Species that look like their ancient fossil relatives (so-called living fossils) have stopped evolving. In fact No. A body form can stay similar for a long time while the species' DNA and allele frequencies keep changing; living species that resemble ancient fossils are themselves the product of continued evolution.
Students often think Humans have stopped evolving, because modern medicine and technology let almost everyone survive. In fact No. Medicine changes which traits affect survival and reproduction, but mutation, genetic drift, migration and selection still act on human populations, so allele frequencies continue to change.
9 more questions. Every wrong answer here is a real mistake students make, and you see why it is wrong as soon as you answer.
Question 1 of 9
Researchers studied beetles of a hypothetical species on two farms: one sprayed with a pesticide every year since 2014 and one never sprayed. In 2016 and in 2022 they exposed samples of beetles from each farm to a standard dose of the pesticide. The graph shows the mean percentage of beetles that survived; error bars show ±2 SE of the mean. Which conclusion is supported by the data?
Answer and reasoning
AOnly in 2022 do the data show a likely difference in survival between the two farms.Correct In 2016 the bars overlap (sprayed 7 to 17%, unsprayed 5 to 13%), so the data show no clear difference. In 2022 they do not overlap (42 to 54% and 7 to 15%), so survival was likely higher on the sprayed farm, as expected if resistance had evolved there.
BIn 2016, survival was the same on the two farms, as their error bars overlap. A student who thinks overlapping error bars prove equal means picks this. Overlap means only that the data show no significant difference in 2016, not that survival was identical.
CIn both years, survival was likely higher on the sprayed farm, as its mean was higher. A student who treats any difference in means as real picks this. In 2016 the difference between 12% and 9% is within the overlapping error bars and could be due to chance.
DBeetles on the sprayed farm became resistant through their repeated exposure to the pesticide. A student who thinks individuals acquire resistance through exposure picks this. Beetles tested in 2022 are descendants of earlier beetles; resistance spreads because beetles that already carry resistance alleles survive spraying and leave more offspring.
Working ±2 SE ranges. 2016: sprayed 12 ± 5 = 7 to 17%; unsprayed 9 ± 4 = 5 to 13%: overlap, no evidence of a difference. 2022: sprayed 48 ± 6 = 42 to 54%; unsprayed 11 ± 4 = 7 to 15%: no overlap, likely difference.
In a weed population of a hypothetical plant species, an allele gives resistance to herbicide H. Where the herbicide is not used, resistant plants produce fewer seeds than susceptible plants. After years of spraying with H, most plants in a field carry the allele. The farmer then stops using H. Which prediction about the resistance allele over the following generations is best supported?
Answer and reasoning
AIts frequency will stay the same, as evolution moves forward and does not reverse. A student who sees evolution as one-way progress picks this. Selection favors whatever variants leave more offspring now; without the herbicide, that is the susceptible plants, so the allele declines.
BIts frequency will decline over generations, as resistant plants leave fewer offspring than others.Correct Without the herbicide, the allele no longer helps its carriers and costs them seeds, so plants without it leave more offspring and the allele becomes less common, generation by generation.
CEach resistant plant will lose its resistance once the herbicide is not sprayed on it. A student who thinks individuals gain or lose traits through exposure picks this. A plant's alleles do not change when spraying stops; the change happens across generations as the allele's frequency falls.
DIt will disappear in the next generation, as it now gives the plants that carry it no benefit. A student who pictures selection as all-or-nothing picks this. Resistant plants still produce seeds, only fewer, so the allele declines gradually over many generations.
A survey found that weeds of a hypothetical species from farms that had sprayed herbicide H for ten years survived spraying more often than weeds from farms that had never used H. A researcher proposes that spraying selected for resistance. Which new investigation would best test this proposal?
Answer and reasoning
ASurvey weeds on many more farms to confirm that weeds from sprayed farms survive spraying more often than others. A student who thinks more observations of an association prove its cause picks this. Sprayed and unsprayed farms may differ in other ways; only an experiment that controls these factors tests the cause.
BSpray plants grown from one susceptible seed stock once, then test whether survivors became resistant during spraying. A student who thinks individuals become resistant through exposure picks this. Selection acts across generations on inherited variation; one spraying of one generation cannot show an evolutionary change in the population.
CGrow several populations from one susceptible seed stock, spray all of them each generation, and record survival over ten generations. A student who thinks a control group is unnecessary picks this. Without unsprayed populations for comparison, a change in survival could not be attributed to spraying.
DGrow several populations from one susceptible seed stock, spray half each generation, and compare survival after ten generations.Correct Starting all populations from the same seed stock and spraying only half makes spraying the only difference between groups, and the unsprayed populations show what happens without it. Greater survival in the sprayed lines after ten generations would show that spraying selected for resistance.
Working Independent variable: spraying with H (sprayed vs unsprayed populations). Control: unsprayed populations from the same seed stock. Constant: seed stock, growing conditions, number of generations. Dependent variable: survival of spraying after ten generations.
Two populations of a hypothetical bacterium were started from one ancestral cell and grown for 20,000 generations in identical, constant laboratory conditions. Samples were frozen every 5,000 generations, and their genomes were later sequenced. The graph shows the number of differences from the ancestral genome. Which statement best describes the data?
Answer and reasoning
AThe number of differences rose at first and then stopped once the populations were adapted. A student who thinks evolution stops once a population is adapted picks this. The lines keep rising at a nearly constant slope up to 20,000 generations; they do not level off.
BThe number of differences rose steadily in both populations throughout the experiment.Correct Both populations gained about 8 to 11 differences in every 5,000 generations, from 0 to 41 and from 0 to 39, with no leveling off: their genomes kept changing throughout the experiment.
CThe two populations gained identical mutations, since they lived in identical conditions. A student who thinks the environment determines which mutations occur picks this. The graph shows different numbers of differences (41 and 39), and mutations arise at random, so identical conditions do not produce identical genomes.
DThe rate of accumulating differences rose with each 5,000 generations that passed. A student who reads a rising line as a rising rate picks this. The slope, which is the rate of change, stays about the same (about 10 differences per 5,000 generations); the number of differences rises because mutations keep accumulating at a steady rate.
Influenza vaccines are updated most years to match the strains of influenza virus expected to circulate. Which explanation best accounts for the need to update them?
Answer and reasoning
AInfluenza keeps evolving, as mutations alter its surface proteins and variants that escape immunity spread.Correct Random mutations during replication change the virus's surface proteins. Variants that are not recognized by immunity from earlier infections or vaccines infect more people and spread, so the virus population keeps changing.
BVaccination causes the virus to mutate into new strains so that it can escape the vaccine. A student who thinks pathogens mutate in response to a challenge picks this. Mutations arise at random; immunity only favors variants that already carry changes that let them escape it.
CPeople become resistant to a vaccine after receiving it, so a new vaccine is needed each year. A student who thinks the person becomes resistant picks this. It is the virus population that changes; the vaccine is updated to match the new viral variants.
DThe virus becomes more dangerous every year, as evolution makes pathogens steadily stronger. A student who sees evolution as steady progress picks this. Evolution has no direction toward 'stronger' pathogens; new variants spread because they escape existing immunity.
Fossil horseshoe crabs about 150 million years old look very similar to the horseshoe crabs living today. A student claims that horseshoe crabs have stopped evolving. Which reasoning best counters this claim?
Answer and reasoning
AEach crab's phenotype changes as it molts and grows, and this change is evolution. A student who thinks individual change is evolution picks this. Molting and growth are changes within one animal's life; evolution is change in a population's allele frequencies over generations.
BCrab populations in different seas differ in size, and this difference shows evolution. A student who counts every difference as evolution picks this. Size can differ because of food or temperature; a difference is evidence of evolution only if it is inherited.
CCrab populations are still evolving, moving toward a more advanced body form. A student who sees evolution as progress picks this. Evolution has no direction toward advanced forms; the counterargument rests on continuing genetic change, not on progress.
DEvolution goes on, as DNA and allele frequencies change while body form stays similar.Correct Evolution is change in allele frequencies, not only in body form. Mutation, drift and selection continue to change horseshoe crab DNA and allele frequencies while the body form stays similar, so similar fossils do not show that evolution stopped.
The model shows the surface protein of an original virus found in bats and of a variant that differs from it by one mutation, and whether each protein binds to receptors on bat cells and on human cells. Which explanation of how the variant could cause an emergent disease in humans is best supported by the model?
Answer and reasoning
AContact with human cells caused the virus to change its protein to fit the human receptor. A student who thinks pathogens mutate in response to a new host picks this. The mutation arises at random during replication; contact with human cells only allows a variant that already fits to infect them.
BHuman cells changed their receptors during infection so that they fit the virus's surface protein. A student who thinks organisms change in response to exposure picks this. The model shows the human receptor unchanged; it is the virus's protein that differs.
CA random mutation changed the protein's shape so the variant can bind to human cells.Correct In the model, one mutation changes the shape of the variant's surface protein so that it fits the human receptor as well as the bat receptor. A virus that can bind human cells can infect people and may spread as a new, emergent disease.
DThe virus became more advanced, so it could infect a more complex host such as a human. A student who sees evolution as progress toward more advanced forms picks this. The variant is not more advanced; its protein simply has a shape that fits the human receptor.
A student claims that human populations are still evolving. Which observation provides the best evidence for this claim?
Answer and reasoning
AAdults who drink milk daily gain the ability to digest lactose and pass this ability on to their children. A student who thinks acquired traits are inherited picks this. Drinking milk does not change the DNA in a person's eggs or sperm, so any ability gained this way is not passed on.
BAverage adult height in many countries has risen by several centimeters over the past 150 years. A student who counts any change in a trait as evolution picks this. Most of this rise is attributed to better nutrition and health; a change caused by the environment is not evidence of a change in allele frequencies.
CPeople who move to high altitudes produce more red blood cells within a few weeks of arriving. A student who thinks individual change is evolution picks this. Making more red blood cells is a change within one person's life (acclimatization), not an inherited change in a population.
DAncient DNA shows an allele for digesting lactose as an adult became more common in some populations.Correct A rise in the frequency of an allele over generations is evolution by definition. DNA from ancient remains shows that the lactase persistence allele increased in frequency in some populations over the last few thousand years.
The diagram shows a typical snail shell from each of six samples of one lineage: five fossil samples from successive rock layers and a sample of the living species. Which statement is best supported by the diagram?
Answer and reasoning
ARib number changed gradually through intermediate forms, as each sample has one more rib.Correct From 5 million years ago to the living species, each sample has one more rib than the sample before it (2, 3, 4, 5, 6, 7), with no gaps or reversals: a continuous series of intermediate forms that extends to the living species.
BThe lineage was changing toward an ideal number of ribs, which the living species has reached. A student who sees evolution as progress toward an ideal picks this. Nothing in the diagram shows a target; the living species is one point in a series that has continued to change.
CThe living species has stopped evolving, because it is the final form in the sequence shown. A student who thinks living species are the finished end points of evolution picks this. The diagram ends at the present only because that is when the sample was taken; the lineage changed right up to it.
DEach snail added ribs to its shell as it aged, so older snails ended up with more ribs. A student who thinks individual change is evolution picks this. Each sample shows a typical shell from one time; the series compares populations across millions of years, not one snail at different ages.
Compiled from the AP Biology Course and Exam Description (effective Fall 2025) and our question bank · Specialist review in progress. How these pages are made · Free, no account
