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19. Phylogeny, Speciation, and Extinction — Practice Questions 2
This chapter explores evolutionary relationships, the mechanisms behind speciation, and the role of extinction in shaping biodiversity.
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(Multiple Choice — Click to Reveal Answer)
1. What is the primary reason molecular clocks are considered more accurate than fossil records in dating evolutionary events?
(A) Molecular clocks are unaffected by geological processes
(B) Fossils are always incomplete
(C) Molecular clocks rely on convergent traits
(D) Fossils only exist for extinct species
Answer
(A) — Molecular clocks are based on constant mutation rates and are less impacted by external events compared to fossil evidence.
2. In a phylogenetic tree, what does the root represent?
(A) The most recent common ancestor
(B) The extinction event
(C) The outgroup
(D) The original common ancestor of all included species
Answer
(D) — The root is the base of the tree and represents the last universal common ancestor (LUCA) of all taxa shown.
3. What would likely happen to two isolated populations experiencing different environmental pressures over a long time?
(A) They will merge
(B) They will become extinct
(C) They will undergo sympatric speciation
(D) They will accumulate differences and potentially speciate
Answer
(D) — Different selection pressures can lead to reproductive isolation and eventual speciation.
4. Which of the following best describes punctuated equilibrium?
(A) Gradual accumulation of genetic changes
(B) Rapid bursts of speciation followed by long periods of stasis
(C) Random gene flow across populations
(D) Constant extinction and recovery rates
Answer
(B) — Punctuated equilibrium proposes that evolution occurs in rapid events separated by long periods of little change.
5. Which factor most directly contributes to adaptive radiation after a mass extinction event?
(A) Increased gametic isolation
(B) Reduced mutation rate
(C) Availability of unoccupied ecological niches
(D) Stronger hybrid breakdown
Answer
(C) — After mass extinctions, many niches open up, allowing surviving species to diversify rapidly.
6. Which of the following is an example of sympatric speciation?
(A) Lizards separated by a canyon evolve independently
(B) Fish in a lake develop distinct mating preferences despite no physical barriers
(C) Birds blown to a new island form a separate population
(D) Wolves migrate into a new region and interbreed
Answer
(B) — Sympatric speciation occurs without geographic isolation, often through behavioral or genetic changes within the same area.
7. What is the best evidence that two species share a recent common ancestor?
(A) They live in the same area
(B) They share similar diets
(C) They have very similar DNA sequences
(D) They can interbreed
Answer
(C) — High similarity in DNA sequences indicates a recent divergence from a common ancestor.
8. A group that includes a common ancestor and some, but not all, of its descendants is called:
(A) Monophyletic
(B) Polyphyletic
(C) Paraphyletic
(D) Homologous
Answer
(C) — A paraphyletic group includes the common ancestor but not all of its descendants.
9. Which of the following supports the biological species concept?
(A) Organisms that share a niche are the same species
(B) Species are defined by morphological differences
(C) Species are defined by the ability to interbreed and produce fertile offspring
(D) Species have similar fossil records
Answer
(C) — The biological species concept focuses on reproductive isolation and interbreeding potential.
10. What is a synapomorphy?
(A) A trait shared with the outgroup
(B) A unique ancestral trait
(C) A shared derived trait that defines a clade
(D) A trait that re-evolves in a descendant species
Answer
(C) — Synapomorphies are shared derived traits used to define clades in phylogenetic analysis.
11. What kind of trait is most useful in constructing a phylogenetic tree?
(A) Analogous trait
(B) Homologous trait
(C) Vestigial trait
(D) Behavioral trait
Answer
(B) — Homologous traits arise from shared ancestry and provide insight into evolutionary relationships.
12. Which of the following is a likely consequence of reduced genetic diversity?
(A) Increased rate of speciation
(B) Greater adaptability
(C) Higher extinction risk
(D) Broader ecological range
Answer
(C) — Reduced genetic diversity limits adaptability and increases extinction risk, especially during environmental changes.
13. Which of the following reproductive barriers occurs after fertilization?
(A) Temporal isolation
(B) Gametic isolation
(C) Hybrid sterility
(D) Mechanical isolation
Answer
(C) — Hybrid sterility is a postzygotic barrier; the offspring is produced but cannot reproduce.
14. Which event most directly triggers extinction on a wide scale?
(A) Seasonal changes
(B) Global climate shifts or asteroid impact
(C) Mutation accumulation
(D) Local competition
Answer
(B) — Sudden, global-scale environmental changes can cause mass extinctions across many species.
15. Which term describes the independent evolution of similar traits in unrelated lineages?
(A) Homology
(B) Divergence
(C) Convergent evolution
(D) Adaptive radiation
Answer
(C) — Convergent evolution results in similar traits in different lineages due to similar environmental pressures.
16. Which of the following would best support the theory of punctuated equilibrium?
(A) Gradual fossil changes over time
(B) A fossil record showing long stasis interrupted by sudden appearance of new species
(C) Continuous genetic drift
(D) Constant morphological changes in all lineages
Answer
(B) — Punctuated equilibrium is characterized by rapid change followed by long periods with little to no change.
17. What role does reproductive isolation play in speciation?
(A) It decreases the chance of extinction
(B) It allows different populations to remain genetically identical
(C) It prevents gene flow, leading to divergence
(D) It ensures environmental adaptation
Answer
(C) — Reproductive isolation blocks gene flow, allowing populations to evolve independently and potentially form new species.
18. What is one limitation of the morphological species concept?
(A) It requires genetic data
(B) It doesn’t apply to fossils
(C) It may group distinct species with similar traits
(D) It cannot be used for extinct organisms
Answer
(C) — Morphological similarity can be misleading when different species look alike but are genetically distinct.
19. Why are analogous traits misleading in phylogenetic analysis?
(A) They suggest shared ancestry when there is none
(B) They only occur in extinct species
(C) They are always environmental
(D) They are used in the biological species concept
Answer
(A) — Analogous traits result from convergent evolution and do not indicate common ancestry.
20. What factor can cause hybrid breakdown in future generations of hybrids?
(A) Chromosomal incompatibility
(B) Behavioral isolation
(C) Temporal divergence
(D) Ecological competition
Answer
(A) — Genetic incompatibilities in hybrid descendants can reduce viability or fertility over successive generations.
21. What would be a likely consequence of low mutation rates across a clade?
(A) Rapid adaptation
(B) Faster evolution
(C) Slower molecular clock changes
(D) More speciation events
Answer
(C) — Low mutation rates result in fewer genetic differences accumulating, which slows molecular divergence over time.
22. What does a branch point (node) on a cladogram signify?
(A) An extinction event
(B) A new mutation
(C) A common ancestor and a speciation event
(D) A trait reversal
Answer
(C) — Each node represents the divergence of two lineages from a common ancestor.
23. How does habitat differentiation contribute to sympatric speciation?
(A) It causes geographic separation
(B) It reduces hybrid fertility
(C) It creates new reproductive barriers within the same location
(D) It increases mutation rates
Answer
(C) — When populations exploit different niches within the same environment, they may diverge reproductively.
24. What does the fossil record primarily tell us about extinction events?
(A) They are caused by mutation
(B) They occur in regular 10,000-year cycles
(C) They are often rapid and widespread
(D) They only affect aquatic organisms
Answer
(C) — Mass extinctions are typically sudden and affect large numbers of species across multiple ecosystems.
25. What is the primary evolutionary consequence of allopatric speciation?
(A) Genetic convergence
(B) Geographic gene flow
(C) Divergence due to reproductive isolation
(D) Extinction of hybrids
Answer
(C) — Geographic isolation prevents gene flow, allowing populations to evolve independently into distinct species.
26. Which of the following best illustrates polyploidy as a mechanism of speciation?
(A) A diploid plant produces sterile offspring
(B) A tetraploid plant forms fertile offspring only with other tetraploids
(C) Two bird species interbreed and form a hybrid
(D) A mutation causes behavioral isolation
Answer
(B) — Polyploidy involves chromosome doubling, creating reproductive isolation from the original population and forming a new species.
27. What is the most likely result when a hybrid individual is less fit than either parent species?
(A) Hybrid reinforcement
(B) Fusion of the species
(C) Hybrid breakdown
(D) Gene flow increases
Answer
(A) — Reinforcement strengthens prezygotic barriers to prevent formation of unfit hybrids.
28. Which scenario best represents a paraphyletic group?
(A) All mammals including their common ancestor
(B) Reptiles excluding birds
(C) A group of species with analogous traits
(D) A lineage that diverged independently
Answer
(B) — Reptiles excluding birds form a paraphyletic group because birds descended from reptiles but are left out.
29. Which condition would most likely increase the rate of speciation in a clade?
(A) Homogeneous environments
(B) Low mutation rate
(C) Wide availability of diverse niches
(D) Strict stabilizing selection
Answer
(C) — Access to new or varied ecological niches promotes diversification and speciation.
30. A population undergoes chromosomal rearrangement that prevents successful meiosis with the original population. What type of isolation has occurred?
(A) Temporal isolation
(B) Gametic isolation
(C) Mechanical isolation
(D) Postzygotic barrier due to genetic incompatibility
Answer
(D) — Structural changes in chromosomes can cause genetic incompatibility and postzygotic isolation.
31. Which of the following increases confidence in the accuracy of a phylogenetic tree?
(A) Using a single morphological trait
(B) Combining morphological, molecular, and fossil data
(C) Ignoring molecular clocks
(D) Using only behavioral traits
Answer
(B) — Using multiple independent lines of evidence provides stronger support for inferred evolutionary relationships.
32. In molecular phylogenetics, what does a higher number of sequence differences between two species suggest?
(A) They share a more recent ancestor
(B) They are likely sister taxa
(C) They diverged further back in time
(D) They evolved convergently
Answer
(C) — More differences in DNA sequences usually indicate a longer time since divergence from a common ancestor.
33. Which factor could obscure the signal of speciation in a phylogenetic analysis?
(A) Long branch attraction due to unequal mutation rates
(B) Use of a rooted tree
(C) Incorporating fossil data
(D) Use of homologous traits
Answer
(A) — Long branch attraction can mislead analyses by grouping rapidly evolving lineages incorrectly due to similar total changes.
34. Which of the following statements is most consistent with the theory of gradualism in evolution?
(A) Evolution occurs in rapid bursts
(B) New species appear suddenly
(C) Speciation is a result of long-term accumulation of small changes
(D) All traits evolve at the same pace
Answer
(C) — Gradualism proposes that evolutionary changes accumulate slowly and steadily over time.
35. Why might a trait that appears homologous actually be analogous upon further study?
(A) It evolved due to similar environments rather than shared ancestry
(B) It exists in the outgroup
(C) It is a vestigial structure
(D) It is found only in fossils
Answer
(A) — Traits shaped by convergent evolution can appear similar but evolved independently, making them analogous rather than homologous.
36. Explain why prezygotic barriers are considered more efficient in preventing gene flow than postzygotic barriers.
Answer
Prezygotic barriers prevent fertilization from occurring, which avoids the energy cost of producing unfit or sterile offspring. They act earlier in the reproductive process and are more effective at maintaining species boundaries.
37. How can ecological isolation lead to speciation even when populations share the same geographic area?
Answer
Ecological isolation occurs when populations use different habitats or resources within the same area, limiting encounters and mating opportunities, which may eventually lead to reproductive isolation and speciation.
38. What is the difference between homologous and analogous traits in terms of evolutionary origin?
Answer
Homologous traits are inherited from a common ancestor, while analogous traits arise independently in unrelated species due to similar environmental pressures.
39. Describe one way that molecular data can improve the accuracy of a phylogenetic tree.
Answer
Molecular data, such as DNA or protein sequences, provide quantifiable genetic similarities and differences that can reveal evolutionary relationships not evident from morphology alone.
40. Why might polyploidy lead to immediate speciation in plants?
Answer
Polyploidy results in offspring with a different number of chromosomes, which can create reproductive isolation from the parent population and form a new species in a single generation.
41. How does the concept of reinforcement strengthen prezygotic reproductive barriers?
Answer
If hybrids have reduced fitness, natural selection favors individuals that avoid interbreeding, thereby reinforcing traits that prevent mating between species.
42. What evidence in the fossil record supports the idea of punctuated equilibrium?
Answer
The fossil record often shows long periods of little change (stasis) interrupted by abrupt appearances of new species, supporting the model of punctuated equilibrium.
43. How does a monophyletic group differ from a polyphyletic group in cladistics?
Answer
A monophyletic group includes a common ancestor and all its descendants, while a polyphyletic group lacks a common ancestor and consists of unrelated organisms grouped by similar traits.
44. Describe one scenario where a hybrid zone remains stable over time.
Answer
A hybrid zone may remain stable when hybrids are viable but less fit than parent species. This allows limited gene flow but maintains distinct species boundaries.
45. Why is the use of multiple genes or loci preferred in constructing phylogenetic trees?
Answer
Using multiple genes reduces the effect of anomalies in individual gene trees, providing a more robust and accurate estimate of species relationships.
46. What is one challenge of using the biological species concept for asexual organisms?
Answer
The biological species concept relies on interbreeding and reproductive isolation, which cannot be applied to asexual organisms that do not reproduce through mating.
47. Explain how adaptive radiation leads to increased biodiversity.
Answer
Adaptive radiation allows a single ancestral species to diversify rapidly into multiple species, each adapted to a unique ecological niche, increasing biodiversity.
48. What is the significance of a shared derived character in a phylogenetic tree?
Answer
Shared derived characters are used to define clades and indicate evolutionary relationships by showing traits inherited from a common ancestor unique to that group.
49. How can long branch attraction lead to errors in phylogenetic inference?
Answer
Long branch attraction causes distantly related lineages with high mutation rates to appear falsely related due to similar accumulated changes, distorting tree topology.
50. Describe one reason why extinction is considered a natural part of evolution.
Answer
Extinction removes species that are less fit or poorly adapted, clearing ecological space and driving evolutionary innovation in surviving lineages.