What is Evolution on the Living Environment Regents?

Evolution is a Evolution topic on the Living Environment Regents. RegentsLab has 20 practice questions on it, each with a full worked solution.

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Evolution: Living Environment Regents Practice

Practice Evolution for the Living Environment Regents with real-style questions and full worked solutions. Miss one? Read the solution — the exam reuses the same ideas every year.

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Question 33 · 2 pts

According to modern evolutionary theory, what is the original source of the new inheritable variations on which natural selection acts?

(A) Changes produced by the use and disuse of body parts
(B) Behaviors that an organism learns and then teaches its offspring
(C) The needs of an organism during its lifetime
(D) Random mutations in the genetic material ✓

Worked solution

$\text{Natural selection acts on heritable variation that is already present; it does not create variation.}$ Selection is a filter, not a source.

$\text{New alleles (new heritable variations) arise from random changes in DNA, called mutations.}$

$\text{Sexual reproduction then recombines these variations, but the original source is mutation.}$

Answer: Random mutations in the genetic material

Mutations randomly alter DNA and are the ultimate source of new heritable variation; sexual reproduction later shuffles these variations among offspring.

Question 34 · 2 pts

A population of rabbits produces many more offspring than the environment can support, and most of these offspring do not survive to reproduce. This overproduction of offspring is important to evolution because it

(A) ensures that all of the offspring are genetically identical to the parents
(B) guarantees that every rabbit will find enough food and shelter
(C) causes the rabbits to mutate so that they can survive the shortage
(D) increases competition, so individuals with favorable variations are more likely to survive and reproduce ✓

Worked solution

$\text{Resources are limited, so overproduction leads to a struggle for existence (competition).}$

$\text{Individuals vary; those with favorable heritable variations are more likely to survive and reproduce.}$

$\text{Their advantageous alleles become more common in the next generation (differential survival).}$

Answer: increases competition, so individuals with favorable variations are more likely to survive and reproduce

Overproduction plus limited resources creates competition, allowing natural selection to favor individuals whose inherited variations make them better suited to the environment.

Question 44 · 2 pts

A single species of lizard lived in one region until a wide river permanently split the population into two separated groups. After many thousands of years, the two groups had become so different that they could no longer interbreed to produce fertile offspring. This formation of a new species is best described as...

(A) extinction of the original population
(B) a temporary, nonheritable adjustment to the environment
(C) artificial selection carried out by humans
(D) speciation resulting from geographic isolation ✓

Worked solution

$\text{Barrier (river)} \rightarrow \text{no gene flow between groups}$ The river geographically isolates the two groups so they can no longer interbreed.

$\text{Separate selection} + \text{time} \rightarrow \text{reproductive isolation} \rightarrow \text{new species}$ Independent genetic changes accumulate until the groups can no longer produce fertile offspring.

Answer: speciation resulting from geographic isolation

When a physical barrier separates a population and gene flow stops, the groups can accumulate enough differences to become reproductively isolated new species.

Question 46 · 2 pts

In a column of undisturbed sedimentary rock, fossils of simple organisms are found in the deepest layers and fossils of more complex organisms are found in the upper layers. Which conclusion is best supported by this pattern?

(A) Life forms have changed over time, and the deeper layers contain the older organisms. ✓
(B) The complex organisms in the upper layers are older than the simple organisms below them.
(C) Fossils give no reliable information about the history of life.
(D) All of these organisms appeared on Earth at the same time.

Worked solution

$\text{Undisturbed strata: deeper} = \text{older}$ Lower layers were deposited first, so they are older than the layers above them.

$\text{simple (deep, old)} \rightarrow \text{complex (shallow, recent)}$ The vertical fossil sequence records change in life forms over time.

Answer: Life forms have changed over time, and the deeper layers contain the older organisms.

In undisturbed sedimentary rock, deeper layers are older, so the fossil sequence records how life has changed over long periods of time.

Question 28 · 1 pt

A population of beetles lives on dark tree bark. Over many generations, dark-colored beetles become far more common than light ones. This change is best explained by

(A) the beetles choosing to change color
(B) an increase in mutation rate
(C) asexual reproduction
(D) natural selection ✓

Worked solution

$\text{camouflaged} \Rightarrow \text{survive} \Rightarrow \text{reproduce}$ Better-adapted variants pass on their genes.

Answer: \text{natural selection}

Dark beetles are better camouflaged, so they survive and reproduce more, shifting the population over generations, natural selection acting on variation.

Question 35 · 2 pts

The table below shows the number of differences in the amino acid sequence of the same protein when each of four species is compared with species $X$. | Species | Amino acid differences from $X$ | |---|---| | $P$ | 22 | | $Q$ | 5 | | $R$ | 13 | | $S$ | 31 | Based only on these data, which species is most closely related to species $X$?

(A) Species Q ✓
(B) Species S
(C) Species P
(D) Species R

Worked solution

$\text{Fewer differences in the same protein indicate a more recent common ancestor (closer relationship).}$

$\min(22,\ 5,\ 13,\ 31) = 5$ The smallest number of amino acid differences belongs to species Q.

$\text{Therefore species } Q \text{ is most closely related to species } X.$

Answer: Species Q

The more similar the amino acid (or DNA) sequences of two species, the more closely related they are, because fewer molecular differences imply a more recent common ancestor.

Question 36 · 2 pts

A doctor finds that an antibiotic that once cured a certain bacterial infection no longer works against it. Which statement best explains, in terms of natural selection, how the bacterial population became resistant to the antibiotic?

(A) All of the bacteria became resistant at the same time and to the same degree
(B) The bacteria chose to become resistant so they would not be killed
(C) The antibiotic caused each bacterium to develop the resistance it needed to survive
(D) A few bacteria already carried resistance alleles; when the antibiotic was used, these bacteria survived and reproduced, passing resistance to their offspring ✓

Worked solution

$\text{Random mutation already produced variation: a few bacteria had resistance alleles before treatment.}$

$\text{The antibiotic acts as a selective agent, killing non-resistant bacteria.}$

$\text{Resistant survivors reproduce, so the resistance allele becomes more common in the population.}$

Answer: A few bacteria already carried resistance alleles; when the antibiotic was used, these bacteria survived and reproduced, passing resistance to their offspring

Antibiotic resistance is natural selection: pre-existing genetic variation lets some bacteria survive the antibiotic and pass that advantageous allele to offspring, increasing its frequency over generations.

Question 38 · 2 pts

The forelimbs of humans, whales, and bats all contain the same basic arrangement of bones, even though these limbs are used for grasping, swimming, and flying. Biologists consider this similarity to be evidence that these organisms

(A) each developed identical limb bones because they all needed limbs
(B) all live in the same type of environment
(C) share a common ancestor ✓
(D) are all members of the same species

Worked solution

$\text{Structures with the same underlying bone pattern but different functions are called homologous structures.}$

$\text{Homologous structures are inherited from a shared ancestor and later modified for different uses.}$

$\text{Therefore the shared limb pattern is evidence of common ancestry.}$

Answer: share a common ancestor

Homologous structures share the same basic anatomy because the organisms inherited it from a common ancestor, even though natural selection later adapted the structure for different functions.

Question 40 · 2 pts

For thousands of years, dairy farmers have increased milk output by allowing only their highest-producing cows to reproduce. This practice is best described as

(A) artificial selection, in which humans choose which organisms reproduce ✓
(B) a mutation in the cows that is caused by the act of milking them
(C) evolution that occurs even though allele frequencies in the herd never change
(D) natural selection, in which the environment alone determines which organisms survive and reproduce

Worked solution

$\text{Humans, not the natural environment, decide which cows reproduce.}$ Human choice is the key feature of selective breeding.

$\text{Choosing the highest milk producers passes their alleles to the next generation.}$

$\text{Over many generations the favored alleles increase in frequency; this is artificial selection (selective breeding).}$

Answer: artificial selection, in which humans choose which organisms reproduce

Selective breeding is artificial selection: humans choose which individuals reproduce based on desired traits, shifting allele frequencies in the population over generations, much as natural selection does in the wild.

Question 43 · 2 pts

A population of bacteria is treated with an antibiotic. At first the antibiotic kills almost all of the bacteria, but after several generations nearly the entire population is resistant to the antibiotic. Which statement best explains this increase in resistance?

(A) Each bacterium changed its own genes during its lifetime to become resistant.
(B) The bacteria became resistant because they wanted to avoid being killed.
(C) The antibiotic caused the bacteria to develop resistance because they needed it to survive.
(D) A few bacteria already carried a resistance variation; these survived, reproduced, and passed the trait to their offspring. ✓

Worked solution

$\text{Variation exists first} \rightarrow \text{selection acts on it}$ Resistance variation was already present in a few bacteria, arising from random mutation before exposure.

$\text{Resistant survive} \rightarrow \text{reproduce} \rightarrow \text{pass trait}$ The antibiotic is the selecting agent; survivors pass resistance alleles to offspring, raising the trait's frequency.

Answer: A few bacteria already carried a resistance variation; these survived, reproduced, and passed the trait to their offspring.

Natural selection acts on variation that already exists in a population; the environment selects favorable variants rather than creating them on demand.

Question 45 · 2 pts

Which process is the original source of the new heritable variations that natural selection acts upon?

(A) overproduction of offspring
(B) sexual reproduction (recombination)
(C) competition among organisms
(D) gene mutation ✓

Worked solution

$\text{New allele} \Leftarrow \text{change in DNA base sequence (mutation)}$ Only a mutation can produce a genuinely new allele in a population.

$\text{Recombination} \rightarrow \text{shuffles existing alleles, adds no new alleles}$ Sexual reproduction increases combinations, but mutation is the ultimate source of new variation.

Answer: gene mutation

Gene mutations are the original source of new alleles; sexual reproduction then shuffles this variation, and natural selection acts on the resulting differences.

Question 47 · 2 pts

The forelimb of a human (arm), the flipper of a whale, and the wing of a bat all contain the same basic arrangement of bones, even though each limb carries out a different function. This underlying structural similarity is best explained by...

(A) the three animals living in the same habitat
(B) coincidence with no evolutionary significance
(C) the three limbs all performing the same function
(D) descent from a common ancestor ✓

Worked solution

$\text{same bone plan} + \text{different functions} \Rightarrow \text{homologous structures}$ Homologous structures share a common underlying anatomy despite being used differently.

$\text{homology} \Rightarrow \text{common ancestry}$ The shared bone pattern was inherited from a shared ancestor and later modified.

Answer: descent from a common ancestor

Homologous structures share the same basic anatomy because the organisms inherited that structure from a common ancestor, even though it was modified for different functions.

Question 6 · 2 pts

In a population of beetles, some individuals have a color pattern that makes them harder for predators to see against tree bark. Over many generations, this camouflaged color pattern becomes more common in the population. This change is best explained by

(A) beetles intentionally changing their color to avoid predators
(B) natural selection favoring beetles with traits suited to their environment ✓
(C) an equal survival rate for all color patterns of beetles
(D) a mutation that occurs in every beetle in direct response to predators

Worked solution

$Variation in color pattern already exists in the beetle population due to random mutations and genetic recombination.$ existing variation

$Camouflaged beetles are less likely to be eaten by predators, so they survive longer and reproduce more successfully.$

$Over many generations, the genes for the camouflaged pattern increase in frequency, a result of natural selection, not an organism choosing to change.$

Answer: natural selection favoring beetles with traits suited to their environment

Natural selection acts on existing heritable variation; individuals with traits that improve survival and reproduction, such as camouflage, pass those traits on more often, shifting the traits of the population over time.

Question 15 · 2 pts

In a population of beetles, a mutation results in some individuals having a darker body color that camouflages them from predators on dark tree bark. Over many generations, the percentage of dark beetles in the population increases. This change is best explained by

(A) use and disuse of body structures being passed to offspring
(B) natural selection favoring beetles with a survival advantage in that environment ✓
(C) beetles actively choosing to change their color to avoid predators
(D) genetic engineering performed by researchers studying the beetles

Worked solution

$A random mutation created variation, dark body color, already present in the population.$ Source of variation

$Dark beetles are better camouflaged, so they are less likely to be eaten and more likely to survive and reproduce.$ Differential survival

$Beetles that survive pass the dark-color allele to more offspring than lighter beetles do.$ Differential reproduction

$Over many generations, the frequency of the dark-color allele increases in the population.$ Natural selection

Answer: natural selection favoring beetles with a survival advantage in that environment

This is a classic example of natural selection, in which an inherited variation that increases survival and reproductive success becomes more common in a population over time; organisms cannot choose to change their traits, and no researcher intervention is described.

Question 37 · 2 pts

A single species of squirrel lived in one area until a deep canyon formed, splitting the population into two groups that could no longer interbreed. After many thousands of years, the two groups are so different that they cannot produce fertile offspring even when brought back together. This situation is best described as

(A) selective breeding of the squirrels carried out by the canyon environment
(B) the formation of two new species through geographic isolation followed by reproductive isolation ✓
(C) evidence that the squirrels changed their own genes on purpose to become two species
(D) an example of one population that is still a single species despite the canyon

Worked solution

$\text{The canyon causes geographic isolation, stopping gene flow between the two groups.}$

$\text{Over time, mutation and natural selection cause genetic differences to accumulate independently in each group.}$ Long time spans allow gradual divergence.

$\text{When the groups can no longer interbreed to produce fertile offspring, they are reproductively isolated and are now separate species.}$

Answer: the formation of two new species through geographic isolation followed by reproductive isolation

Speciation occurs when a barrier geographically isolates populations, genetic differences accumulate over time, and the groups become reproductively isolated, meaning they can no longer interbreed to produce fertile offspring.

Question 39 · 2 pts

Two populations of the same plant species grow in a region where a new plant disease has just appeared. Population 1 has a great deal of genetic variation, while Population 2 has very little genetic variation. Which population is more likely to survive the disease as a species over time, and why?

(A) Population 1, because its plants will mutate the exact resistance alleles they need once the disease arrives
(B) Both populations equally, because genetic variation has no effect on survival
(C) Population 2, because having little variation means all of the plants are equally strong
(D) Population 1, because greater genetic variation increases the chance that some individuals already carry alleles for disease resistance ✓

Worked solution

$\text{Natural selection can only favor traits that already exist in the population's gene pool.}$

$\text{More genetic variation} \Rightarrow \text{higher probability that some individuals carry resistance alleles.}$

$\text{Resistant individuals survive and reproduce, so the population can adapt; Population 1 is more likely to persist.}$

Answer: Population 1, because greater genetic variation increases the chance that some individuals already carry alleles for disease resistance

Greater genetic diversity makes it more likely that some individuals already possess resistance alleles, so the population can adapt to environmental change such as a new disease through natural selection.

Question 42 · 2 pts

A scientist compares the same protein in three species by counting the number of amino acid differences between each species and a reference organism, Organism $M$. The results are: Species $P = 2$ differences, Species $Q = 14$ differences, and Species $R = 8$ differences. Which species is most likely the most closely related to Organism $M$?

(A) All three are equally related to Organism $M$
(B) Species $Q$
(C) Species $P$ ✓
(D) Species $R$

Worked solution

$\text{Fewer molecular differences} \Rightarrow \text{more recent common ancestor}$ Closely related species have more similar DNA and proteins.

$\min(2,\;14,\;8) = 2 \;\Rightarrow\; \text{Species } P$ Species P has the fewest amino acid differences, so it is most closely related to Organism M.

Answer: Species $P$

The fewer the differences in DNA or protein structure between two organisms, the more closely related they are and the more recently they shared a common ancestor.

Question 48 · 2 pts

In a beetle population, body color varies from light to dark, and color is inherited. The beetles rest on dark tree bark, where birds hunt them by sight. Pollution then kills the pale lichens on the bark, making the bark even darker than before. Over many generations, which outcome does natural selection best predict for this population?

(A) Dark beetles become more common because they are better camouflaged, so they survive and reproduce more often. ✓
(B) Light beetles gradually turn dark during their own lifetimes to hide from the birds.
(C) Light beetles become more common because lighter individuals reproduce more quickly.
(D) The population stays exactly the same because body color cannot be affected by predators.

Worked solution

$\text{darker bark} \rightarrow \text{light beetles more visible to birds}$ The environmental change shifts which color is better camouflaged.

$\text{dark survive} \rightarrow \text{reproduce} \rightarrow \text{frequency of dark trait} \uparrow$ Differential survival and reproduction increase the proportion of dark beetles over generations.

Answer: Dark beetles become more common because they are better camouflaged, so they survive and reproduce more often.

When the environment changes, individuals with the better-camouflaged heritable trait survive and reproduce more, so that trait becomes more common in later generations.

Question 7 · 2 pts

The forelimb bones of a human, a whale, and a bat have a similar arrangement of bones even though the limbs are used for very different functions such as grasping, swimming, and flying. This similarity in bone structure provides evidence that these organisms

(A) share a common evolutionary ancestor ✓
(B) live in identical environments today
(C) developed these structures during their own individual lifetimes in response to use
(D) evolved these limbs completely independently of one another

Worked solution

$Structures with the same underlying bone arrangement but different functions are called homologous structures.$ definition

$Homologous structures are evidence that the organisms that have them descended from a common ancestor, with the structure being modified over time for different functions.$

Answer: share a common evolutionary ancestor

Homologous structures, such as the similar bone pattern in human arms, whale flippers, and bat wings, indicate descent from a common ancestor followed by divergent evolution to serve different functions.

Question 58 · 4 pts · constructed response

In a population of bacteria, a small number of individuals have a gene that makes them resistant to a certain antibiotic. After the antibiotic is used repeatedly over several years, most of the bacteria in the population become resistant to it. Explain how natural selection accounts for this increase in antibiotic resistance in the population.

Model answer: Within the original population, genetic variation already existed, with a few bacteria carrying a resistance gene. When the antibiotic was applied, susceptible bacteria were killed while resistant bacteria survived and reproduced, passing the resistance gene to their offspring. Over many generations, resistant bacteria made up an increasing proportion of the population because they had a survival and reproductive advantage in the presence of the antibiotic.

Worked solution

$\text{Genetic variation exists: some bacteria already carry a resistance allele}$ Variation is the raw material for selection

$\text{Antibiotic acts as a selecting agent}$ Environmental pressure

$\text{Susceptible bacteria die; resistant bacteria survive and reproduce}$ Differential survival/reproduction

$\text{Resistance allele frequency increases each generation}$ Selection changes allele frequencies over time

$\text{Result: most of population becomes resistant}$ Outcome after repeated selection over years

Answer: Within the original population, genetic variation already existed, with a few bacteria carrying a resistance gene. When the antibiotic was applied, susceptible bacteria were killed while resistant bacteria survived and reproduced, passing the resistance gene to their offspring. Over many generations, resistant bacteria made up an increasing proportion of the population because they had a survival and reproductive advantage in the presence of the antibiotic.

This is natural selection acting on pre-existing genetic variation: the antibiotic did not create resistance but selected for bacteria that already possessed it, so resistant individuals survived, reproduced, and increased in frequency over generations.

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