Which observation is one of the core principles behind Darwin and Wallace's theory of natural selection?
More offspring are born than can survive
✓
Body parts grow stronger with use and pass on
Parental traits blend evenly in offspring
Species stay fixed and unchanging over time
Correct Answer
More offspring are born than can survive
Natural selection rests on overproduction: populations produce more offspring than resources can support, so individuals compete and those with helpful heritable traits leave more offspring. Body parts grow stronger with use and pass on describes Lamarck's discredited idea of acquired characteristics. Parental traits blend evenly in offspring was the mistaken blending view of heredity of Darwin's time. Species stay fixed and unchanging over time is the static view that natural selection replaced.
Category: Darwin and Natural Selection
Question 2
A 1977 drought on the Galapagos island Daphne Major reduced small, soft seeds far more than large, hard seeds. Afterward, what happened to the average beak size of medium ground finches in the next generation?
It decreased
It increased
✓
It did not change
It fluctuated at random
Correct Answer
It increased
Large-beaked finches could crack the remaining hard seeds and survived better, and because beak size is inherited, their offspring had larger average beaks. It decreased is the opposite of what Peter and Rosemary Grant measured. It did not change would mean no selection occurred, but survival clearly depended on beak size. It fluctuated at random describes drift, not the directional shift caused by the seed supply.
Category: Darwin and Natural Selection
Question 3
What is the ultimate source of new alleles in every population?
Gene flow
Genetic drift
Mutation
✓
Natural selection
Correct Answer
Mutation
A mutation is a change in the DNA sequence of a gene, and it is the only process that creates a brand-new allele. Gene flow moves existing alleles between populations but does not create them. Genetic drift changes the frequencies of alleles that already exist. Natural selection favors or removes existing alleles rather than producing new ones.
Category: Mechanisms of Evolution
Question 4
Which pattern describes a population that is in Hardy-Weinberg equilibrium?
Allele frequencies shift toward the dominant allele
Recessive alleles are gradually eliminated
New alleles appear at a steady rate
Allele frequencies stay constant across generations
✓
Correct Answer
Allele frequencies stay constant across generations
The Hardy-Weinberg principle states that allele frequencies remain the same from generation to generation when no evolutionary force, such as selection, mutation, drift or gene flow, is acting. Allele frequencies shift toward the dominant allele is a common misconception, since dominance alone does not change frequencies. Recessive alleles are gradually eliminated would require selection against them. New alleles appear at a steady rate would mean mutation is acting, which breaks equilibrium.
Category: Population Genetics
Question 5
A population of 50 diploid individuals carries 100 copies of a gene. If 30 of those copies are allele b, what is the frequency of allele b?
0.3
✓
0.6
0.7
0.15
Correct Answer
0.3
Allele frequency is the number of copies of that allele divided by the total number of gene copies, so 30 divided by 100 equals 0.3. The value 0.6 comes from mistakenly dividing 30 by the 50 individuals instead of the 100 gene copies. The value 0.7 is the frequency of the other allele. The value 0.15 comes from dividing 30 by 200, double the actual number of copies.
Category: Population Genetics
Question 6
In which kind of population does genetic drift have the largest effect on allele frequencies?
A very large population
A small, isolated population
✓
A population with abundant food
A population with many migrants
Correct Answer
A small, isolated population
Drift is the effect of chance on allele frequencies, and chance events such as one individual dying before reproducing remove a larger share of the gene pool when the population is small. A very large population buffers chance, so drift is weak there. A population with abundant food is not defined by size, which is what controls drift. A population with many migrants receives a steady inflow of alleles that tends to counteract drift.
Category: Mechanisms of Evolution
Question 7
A hurricane kills most of an island lizard population at random, without regard to any trait. The survivors' alleles now make up the whole gene pool. Which process does this describe?
Founder effect
Directional selection
Bottleneck effect
✓
Gene flow
Correct Answer
Bottleneck effect
The bottleneck effect is a form of genetic drift in which a random catastrophe sharply reduces a population, leaving survivors whose alleles may not represent the original population. Founder effect occurs when a small group leaves to start a new population elsewhere. Directional selection requires that survival depend on a trait, and here survival was random. Gene flow is the movement of alleles between populations through migration.
Category: Mechanisms of Evolution
Question 8
A small group of settlers starts a new population, and the descendants have an unusually high frequency of the allele for Huntington's disease because several original settlers carried it. Which process explains this?
Bottleneck effect
Gene flow
Natural selection
Founder effect
✓
Correct Answer
Founder effect
The founder effect occurs when a few individuals establish a new population and, by chance, carry allele frequencies different from the source population; the Afrikaner population of South Africa is a well-known example. Bottleneck effect involves a disaster shrinking an existing population in place. Gene flow would bring alleles in from another population. Natural selection is an unlikely explanation because Huntington's disease usually appears after the reproductive years, so the allele is barely exposed to selection.
Category: Mechanisms of Evolution
Question 9
Which trend appears in the fossil record of the horse lineage as forests gave way to open grasslands?
Fewer toes, with a central hoof
✓
More toes on each foot
A smaller overall body size
Loss of the grinding teeth
Correct Answer
Fewer toes, with a central hoof
Early horse ancestors such as Eohippus had four toes on the front feet and three on the back, while later forms walked on a single middle toe that became a hoof, suited to running on open ground. More toes on each foot is the reverse of the fossil sequence. A smaller overall body size is also reversed, since early forms were about the size of a dog. Loss of the grinding teeth is wrong because teeth became better suited to grazing.
Category: Evidence of Evolution
Question 10
Some fish that live in dark caves have eyes that cannot see, inherited from sighted ancestors. What kind of structures are these eyes?
Convergent structures
Vestigial structures
✓
Embryonic structures
Newly evolved structures
Correct Answer
Vestigial structures
Vestigial structures are reduced remnants of features that served a purpose in an ancestor, here the working eyes of sighted ancestral fish. Convergent structures are similar features that evolved independently in unrelated groups. Embryonic structures appear during development and may disappear before adulthood, but these eyes persist in adults. Newly evolved structures would be new features rather than remnants of ancestral ones.
Category: Evidence of Evolution
Question 11
An entire gene is copied, so one copy keeps making the original protein while the other copy gradually changes and takes on a new function. What is this event called?
Gene flow
Genetic drift
Gene duplication
✓
Crossing over
Correct Answer
Gene duplication
Gene duplication adds an extra copy of a whole gene, and because the original copy still does its job, the spare copy is free to change through mutation, selection and drift and can evolve a new function. Gene flow is the movement of alleles between populations. Genetic drift is a change in allele frequencies by chance. Crossing over is the normal exchange of matching segments between paired chromosomes in meiosis, which reshuffles alleles; it is not the name for a copied gene that evolves a new function.
Category: Evidence of Evolution
Question 12
Members of one plant family grow naturally in Australia, southern Africa and South America. What best explains this distribution?
Birds carried its seeds across the oceans
It evolved separately on each continent
Early human travelers spread it worldwide
The family existed before Gondwana broke apart
✓
Correct Answer
The family existed before Gondwana broke apart
The plant family Proteaceae was already present on the southern supercontinent Gondwana, so when the landmass split, its members were carried along on the separating continents. Birds carried its seeds across the oceans would not explain the match with the old Gondwanan landmasses. It evolved separately on each continent conflicts with the shared ancestry of the family. Early human travelers spread it worldwide ignores that the distribution is far older than humans.
Category: Evidence of Evolution
Question 13
What does the nearly universal genetic code shared by living organisms suggest?
All life descends from a common ancestor
✓
Life began separately many times
All species face identical environments
Genes cannot change over time
Correct Answer
All life descends from a common ancestor
DNA is the genetic material of all cellular life, and the code that translates it into protein is nearly the same everywhere, which is best explained by inheritance from one common ancestor. Life began separately many times would predict unrelated codes. All species face identical environments is false and would not explain a shared code. Genes cannot change over time contradicts the mutations and gene duplications observed in every lineage.
Category: Evidence of Evolution
Question 14
Under the biological species concept, two groups of organisms belong to the same species when their members can do what?
Share a similar body shape
Interbreed and produce fertile offspring
✓
Live in the same habitat
Eat the same kinds of food
Correct Answer
Interbreed and produce fertile offspring
The biological species concept defines a species as a group of individuals that actually or potentially interbreed and produce fertile offspring. Share a similar body shape is not enough, since unrelated groups can look alike. Live in the same habitat does not decide species membership, because many species share habitats. Eat the same kinds of food is an ecological similarity, not a reproductive test.
Category: Speciation
Question 15
A horse and a donkey can mate, but their offspring, the mule, is sterile. Which kind of reproductive barrier does this illustrate?
Prezygotic barrier
Geographic barrier
Postzygotic barrier
✓
Behavioral barrier
Correct Answer
Postzygotic barrier
A postzygotic barrier acts after fertilization, for example by producing hybrids that are sterile or fail to develop, as with the mule. Prezygotic barrier refers to mechanisms that prevent fertilization in the first place. Geographic barrier refers to physical separation, but horses and donkeys can meet and mate. Behavioral barrier, such as different courtship displays, is a type of prezygotic barrier.
Category: Speciation
Question 16
A river changes course and splits a population of mice into two groups that can no longer meet. Over many generations the groups become separate species. Which kind of speciation is this?
Sympatric speciation
Adaptive radiation
Autopolyploidy
Allopatric speciation
✓
Correct Answer
Allopatric speciation
Allopatric speciation follows geographic separation, which stops gene flow so the populations accumulate different alleles through mutation, selection and drift. Sympatric speciation happens without a geographic barrier. Adaptive radiation describes one ancestor rapidly giving rise to many species that fill different niches. Autopolyploidy is a chromosome-doubling route to new species, usually in plants.
Category: Speciation
Question 17
A plant with a diploid number of 2n = 6 produces diploid gametes because of a meiotic error, and two of those gametes fuse. How many chromosomes does the offspring have?
12
✓
6
9
3
Correct Answer
12
Each diploid gamete carries 6 chromosomes, so two of them fusing gives a tetraploid (4n) offspring with 12 chromosomes, a case of autopolyploidy. The value 6 is the normal diploid number produced by two normal gametes of 3 each. The value 9 would result from one normal gamete fusing with one diploid gamete. The value 3 is the normal haploid gamete number.
Category: Speciation
Question 18
Some apple maggot flies shifted from laying eggs on hawthorn trees to apple trees, and the two groups now mate mainly on their own host trees in the same area. Which kind of speciation may be underway?
Allopatric speciation
Sympatric speciation
✓
Vicariance
Gene flow
Correct Answer
Sympatric speciation
Sympatric speciation occurs within one location, with no geographic barrier; here the flies are divided by host plant preference while living side by side. Allopatric speciation requires geographic separation, which these flies lack. Vicariance is a natural event that physically splits a population. Gene flow is the movement of alleles between populations, which the host preference is reducing.
Category: Speciation
Question 19
Hawaiian honeycreepers descended from one ancestral species and now include birds with thick seed-cracking beaks, long nectar-feeding beaks and sharp insect-catching beaks. Which process produced this diversity?
Genetic bottleneck
Convergent evolution
Adaptive radiation
✓
Gene duplication
Correct Answer
Adaptive radiation
Adaptive radiation occurs when a single founder species spreads into many different niches or isolated habitats and gives rise to many new species, which island chains make especially likely. Genetic bottleneck is a sudden random loss of genetic diversity, not a burst of new species. Convergent evolution involves unrelated groups evolving similar traits, while these birds share one ancestor. Gene duplication is a change in one gene, not a pattern of species formation.
Category: Speciation
Question 20
Which of these is the smallest unit that can evolve?
Individual organisms
Single cells
Whole ecosystems
Populations
✓
Correct Answer
Populations
Evolution is a change in the genetic makeup of a population across generations; an individual's genes are fixed at conception, so changes in a lifetime are development, not evolution. Individual organisms cannot change their inherited alleles. Single cells are even more limited. Whole ecosystems contain many species that each evolve separately as populations.
Category: Misconceptions About Evolution