Rucete ✏ AP Biology In a Nutshell
19. Phylogeny, Speciation, and Extinction — Practice Questions 3
This chapter explores how evolutionary relationships are inferred, how new species arise, and the role extinction plays in shaping biodiversity over time.
Need a quick review?
📘 Go to the Concept Summary
(Multiple Choice — Click to Reveal Answer)
1. Which of the following best illustrates the principle of maximum parsimony in phylogenetics?
(A) Choosing the tree with the most DNA changes
(B) Choosing the tree with the fewest evolutionary steps
(C) Choosing the tree that reflects fossil dates most closely
(D) Choosing the tree that includes extinct species only
Answer
(B) — Maximum parsimony favors the phylogenetic tree that requires the fewest evolutionary changes.
2. What is the most reliable source of evidence when building phylogenetic trees?
(A) Morphological characteristics
(B) Behavioral similarities
(C) DNA and protein sequence data
(D) Fossil record alone
Answer
(C) — Molecular evidence is less subject to convergent evolution and is considered more reliable for determining evolutionary relationships.
3. What defines a clade in a phylogenetic tree?
(A) A group with similar ecological roles
(B) A group of unrelated species with common traits
(C) A common ancestor and all of its descendants
(D) Organisms sharing analogous traits
Answer
(C) — A clade is a monophyletic group that includes a common ancestor and all its descendants.
4. What evidence suggests that two species diverged recently?
(A) They live in similar habitats
(B) They share more behavioral traits than others
(C) Their DNA sequences are nearly identical
(D) Their fossils appear in different geological strata
Answer
(C) — High DNA similarity indicates a more recent common ancestor.
5. Which term describes a group that includes species but excludes a common ancestor?
(A) Monophyletic
(B) Polyphyletic
(C) Paraphyletic
(D) Clade
Answer
(B) — Polyphyletic groups consist of unrelated species that lack a common ancestor in the group.
6. Which of the following would NOT be considered a prezygotic reproductive barrier?
(A) Temporal isolation
(B) Habitat isolation
(C) Gamete incompatibility
(D) Hybrid infertility
Answer
(D) — Hybrid infertility is a postzygotic barrier because it occurs after fertilization.
7. What role does the outgroup play in constructing a cladogram?
(A) It confirms the common ancestor
(B) It defines the root of the tree and helps identify derived traits
(C) It balances the number of branches
(D) It provides fossil dating evidence
Answer
(B) — The outgroup is used to distinguish ancestral from derived traits and root the tree correctly.
8. Which reproductive isolation mechanism occurs when two species mate but their gametes cannot fuse?
(A) Mechanical isolation
(B) Behavioral isolation
(C) Gametic isolation
(D) Habitat isolation
Answer
(C) — Gametic isolation happens when sperm and egg from different species cannot combine, even after mating occurs.
9. What typically causes the formation of a node on a phylogenetic tree?
(A) A fossil discovery
(B) A speciation event
(C) A hybridization event
(D) An extinction
Answer
(B) — A node represents a common ancestor at the point where one species splits into two or more.
10. Which process describes the evolution of many species from a single common ancestor in a short period?
(A) Gene flow
(B) Adaptive radiation
(C) Convergent evolution
(D) Gradualism
Answer
(B) — Adaptive radiation is the rapid evolution of many species from one ancestor as they adapt to different environments.
11. A species of lizard is separated by a newly formed river. Over generations, they develop differences and can no longer interbreed. What has occurred?
(A) Sympatric speciation
(B) Gene flow
(C) Allopatric speciation
(D) Convergent evolution
Answer
(C) — Allopatric speciation occurs when physical separation prevents gene flow and populations diverge into new species.
12. Which of the following best describes convergent evolution?
(A) Two species evolve from a common ancestor
(B) Two unrelated species develop similar adaptations
(C) Two populations become reproductively isolated
(D) Two species undergo hybridization
Answer
(B) — Convergent evolution is when unrelated species independently evolve similar traits due to similar environments.
13. What term is used to describe the gradual accumulation of small changes in a species over time?
(A) Punctuated equilibrium
(B) Mass extinction
(C) Gradualism
(D) Polyploidy
Answer
(C) — Gradualism refers to slow, continuous evolutionary change over long periods.
14. Which condition is most likely to lead to extinction of a species?
(A) High genetic diversity
(B) Wide geographic range
(C) Small population size and low adaptability
(D) Strong prezygotic isolation
Answer
(C) — Small, genetically uniform populations are more vulnerable to environmental changes and extinction.
15. What is the significance of homologous structures in evolution?
(A) They show convergent evolution
(B) They provide evidence of shared ancestry
(C) They indicate similar environments
(D) They always result from adaptation
Answer
(B) — Homologous structures support the idea that species with these traits inherited them from a common ancestor.
16. How does gene flow affect speciation?
(A) It increases the rate of extinction
(B) It promotes reproductive isolation
(C) It maintains genetic similarity between populations
(D) It reduces genetic diversity
Answer
(C) — Gene flow keeps populations similar by exchanging alleles, potentially preventing speciation.
17. What distinguishes behavioral isolation from other types of prezygotic isolation?
(A) It involves temporal mismatch
(B) It is based on courtship behaviors or mating rituals
(C) It prevents fertilization by molecular mismatch
(D) It depends on geography
Answer
(B) — Behavioral isolation occurs when species use different mating behaviors, so they don’t recognize each other as potential mates.
18. Which of the following is a postzygotic barrier to reproduction?
(A) Gametes cannot fuse
(B) Hybrid offspring are sterile
(C) Species have different mating seasons
(D) Courtship behaviors differ
Answer
(B) — Hybrid sterility is a postzygotic barrier because it happens after fertilization.
19. Which is a characteristic of mass extinction events?
(A) They occur gradually over millions of years
(B) They only affect terrestrial species
(C) They result in the disappearance of a large number of species in a short time
(D) They reduce the need for adaptation
Answer
(C) — Mass extinctions are sudden events that eliminate many species rapidly and globally.
20. In phylogenetic trees, what does a longer branch typically represent?
(A) A species with more ancestors
(B) A species with fewer mutations
(C) A longer time or more genetic change since divergence
(D) An extinct lineage
Answer
(C) — Long branches indicate greater evolutionary time or genetic divergence.
21. Which of the following most directly leads to reproductive isolation?
(A) Increased gene flow
(B) Hybrid fertility
(C) Behavioral changes in mating signals
(D) Environmental stability
Answer
(C) — Changes in mating behavior can prevent interbreeding and lead to reproductive isolation.
22. What is the result of hybrid breakdown?
(A) Fertile hybrid offspring
(B) Gradual re-merging of two species
(C) Weak or sterile offspring in future generations
(D) Formation of new populations
Answer
(C) — Hybrid breakdown results in reduced viability or fertility in later generations of hybrids.
23. Which best explains why phylogenies are considered hypotheses?
(A) They are based on absolute truth
(B) They use random groupings
(C) They are constructed using data and can change with new evidence
(D) They reflect individual preferences
Answer
(C) — Phylogenies are scientific hypotheses that can be revised with new molecular, fossil, or morphological evidence.
24. Which evolutionary force is most responsible for the initial divergence of two isolated populations?
(A) Gene flow
(B) Natural selection
(C) Genetic drift
(D) Behavioral isolation
Answer
(C) — In small, isolated populations, genetic drift can rapidly change allele frequencies and promote divergence.
25. What information does a phylogenetic tree provide about extinct species?
(A) The exact date of extinction
(B) Their reproductive methods
(C) Their evolutionary relationships
(D) Their environmental preferences
Answer
(C) — Phylogenetic trees show how extinct species are related to modern and other extinct organisms through shared ancestry.
26. Which of the following best explains how polyphyletic groups misrepresent evolutionary history?
(A) They include all descendants of a common ancestor
(B) They exclude no members of the clade
(C) They include species without a shared recent ancestor
(D) They are based solely on molecular data
Answer
(C) — Polyphyletic groups lump together species that don’t share a recent common ancestor, which leads to inaccurate evolutionary conclusions.
27. What type of evolutionary pattern occurs when one species evolves into several distinct forms that occupy different niches?
(A) Coevolution
(B) Convergent evolution
(C) Adaptive radiation
(D) Genetic drift
Answer
(C) — Adaptive radiation occurs when a single ancestral species rapidly diversifies into multiple forms adapted to specific environments or niches.
28. Which statement is true about cladograms and phylogenetic trees?
(A) All branches represent actual evolutionary time
(B) They are always based solely on fossil records
(C) They are hypotheses about evolutionary relationships
(D) They require observable mating behaviors to construct
Answer
(C) — Phylogenetic trees and cladograms are hypotheses built from data and are subject to change with new evidence.
29. A new trait appears in a single lineage and all its descendants. What is this trait called?
(A) Analogous trait
(B) Homoplasy
(C) Shared ancestral trait
(D) Shared derived trait
Answer
(D) — A shared derived trait (synapomorphy) is a new trait that arose in a lineage and is shared by all its descendants.
30. Which of the following scenarios would support sympatric speciation through sexual selection?
(A) A population is divided by a river
(B) Females prefer males with a specific coloration pattern
(C) Populations experience bottleneck effects
(D) Natural selection favors large body size in all individuals
Answer
(B) — Sexual selection can drive sympatric speciation if mate choice leads to reproductive isolation within the same geographic area.
31. In a hybrid zone, what would most likely cause reinforcement of reproductive barriers?
(A) Hybrid offspring are fertile and fit
(B) Gene flow increases between species
(C) Hybrids have lower fitness than parent species
(D) There are no behavioral differences
Answer
(C) — Reinforcement occurs when hybrids are less fit, selecting for traits that prevent interbreeding between species.
32. Which of the following accurately describes a molecular clock's function?
(A) It measures changes in morphology over time
(B) It estimates divergence times using mutation rates
(C) It times fossil discoveries
(D) It determines geographic distribution
Answer
(B) — A molecular clock estimates how long ago two species diverged based on the number of molecular differences.
33. What is a key assumption when using molecular clocks in evolutionary biology?
(A) Mutation rates are consistent over time
(B) All mutations are beneficial
(C) Gene flow is constant
(D) Traits evolve independently in all lineages
Answer
(A) — Molecular clocks assume a relatively constant mutation rate to estimate divergence times between species.
34. What does the principle of monophyly require for a group of organisms?
(A) Similar habitat use
(B) A common ancestor and all its descendants
(C) No shared derived traits
(D) Limited genetic variation
Answer
(B) — A monophyletic group includes a single common ancestor and all of its descendant species.
35. Which evolutionary process can lead to reproductive isolation in the absence of physical barriers?
(A) Allopatric speciation
(B) Sympatric speciation
(C) Gene flow
(D) Genetic bottleneck
Answer
(B) — Sympatric speciation occurs without geographic separation, often through behavioral, ecological, or genetic isolation within a population.
36. Describe how a phylogenetic tree can be used to identify the most recent common ancestor of two species.
Answer
In a phylogenetic tree, the most recent common ancestor of two species is found at the node where their branches converge. This node represents the divergence point from a shared lineage.
37. Explain how genetic drift can lead to speciation in a small, isolated population.
Answer
In small populations, random changes in allele frequencies due to genetic drift can lead to divergence over time, especially if the population is isolated and gene flow is limited. This can eventually cause reproductive isolation and speciation.
38. What is the role of fossil evidence in constructing phylogenetic trees?
Answer
Fossil evidence provides temporal context and morphological traits that help infer ancestral relationships and calibrate molecular clocks in phylogenetic trees.
39. Why are analogous structures not used to determine evolutionary relationships?
Answer
Analogous structures result from convergent evolution, not shared ancestry. They can mislead phylogenetic analysis because similar functions evolved independently in unrelated species.
40. How does reproductive isolation contribute to the formation of new species?
Answer
Reproductive isolation prevents gene flow between populations. Over time, this leads to genetic divergence, and the populations can evolve into separate species.
41. Define the term “monophyletic group” and give an example.
Answer
A monophyletic group includes a common ancestor and all its descendants. For example, mammals form a monophyletic group because they all descend from a common ancestor and include all mammalian species.
42. What is meant by the term “hybrid zone,” and what outcomes can result from it?
Answer
A hybrid zone is a region where two closely related species meet and produce hybrid offspring. Outcomes include reinforcement (stronger barriers), fusion (species merge), or stability (hybrids persist but species remain distinct).
43. How can sexual selection lead to sympatric speciation?
Answer
If individuals within a population begin to prefer specific traits in mates, this preference can reduce gene flow and lead to reproductive isolation without geographic separation, resulting in sympatric speciation.
44. Why is polyploidy a common cause of speciation in plants but rare in animals?
Answer
Polyploidy results in extra sets of chromosomes, which can instantly create reproductive isolation. Plants tolerate polyploidy better than animals and can reproduce asexually or self-fertilize, aiding in speciation.
45. What is the difference between a shared ancestral trait and a shared derived trait?
Answer
A shared ancestral trait is found in the common ancestor and all its descendants, while a shared derived trait is unique to a particular lineage and defines a clade.
46. Explain how extinction events can drive evolutionary change in surviving species.
Answer
Extinction events remove competitors and open ecological niches, allowing surviving species to diversify and adapt to new environments, often leading to adaptive radiation.
47. What is long branch attraction and how can it affect phylogenetic analysis?
Answer
Long branch attraction is a phylogenetic artifact where rapidly evolving lineages are incorrectly inferred to be closely related due to similar high mutation rates, distorting evolutionary relationships.
48. Describe the difference between allopatric and sympatric speciation.
Answer
Allopatric speciation occurs due to geographic separation, while sympatric speciation happens without physical barriers, often due to behavioral or genetic isolation within the same area.
49. How does the principle of parsimony help construct phylogenetic trees?
Answer
Parsimony favors the tree with the fewest evolutionary changes, assuming that simpler explanations are more likely correct, and helps avoid overcomplicating evolutionary relationships.
50. Why are reproductive barriers essential in maintaining species boundaries?
Answer
Reproductive barriers prevent gene flow between species, maintaining genetic integrity and preventing the collapse or merging of distinct species.