Chapter 22. Phylogeny

Question 1

1. What does a node represent in a phylogenetic tree, and why is it significant?

Answer 1

• A node represents a point where a single ancestral lineage splits into two or more descendant lineages. It is significant because it indicates the most recent common ancestor shared by the species on different branches of the tree.

Question 2

2. How do phylogenetic trees act as hypotheses?

Answer 2

• Phylogenetic trees are hypotheses because they represent the current understanding of evolutionary relationships based on available data, such as morphology or molecular evidence. As new information becomes available, these hypotheses can be revised.

Question 3

3. What is speciation, and how is it represented on a phylogenetic tree?

Answer 3

• Speciation is the process by which populations of the same species become reproductively isolated and diverge to form new species. On a phylogenetic tree, speciation is represented by a node where a single branch splits into two or more branches.

Question 4

4. Why do we say that phylogenetic trees reveal “nested similarities” among species?

Answer 4

• Phylogenetic trees reveal nested similarities because the branching pattern shows groups of species sharing traits that were inherited from common ancestors. As the tree branches further, the shared traits become more specific to smaller groups of species.

Question 5

5. What kind of data can cause changes in the structure of a phylogenetic tree?

Answer 5

• New molecular data, such as DNA sequencing, can cause changes in a phylogenetic tree. If new evidence suggests that certain species are more closely related than previously thought, the tree can be updated to reflect those relationships.

Question 6

6. Explain the concept of a “universal tree of life” and its importance.

Answer 6

• The universal tree of life is a phylogenetic tree that represents the evolutionary relationships of all living organisms. It shows how all species are connected through common ancestry and highlights the shared evolutionary history of all life forms on Earth.

Question 7

7. Why are speciation events considered important when interpreting a phylogenetic tree?

Answer 7

• Speciation events are critical because they mark the points where one species diverges into two or more distinct species. These events are reflected in the tree’s branching structure, which shows how evolutionary lineages split and form new species over time.

Question 8

8. What role do molecular data and anatomical characteristics play in building phylogenetic trees?

Answer 8

• Molecular data (such as DNA sequences) and anatomical characteristics provide the evidence needed to determine evolutionary relationships. These features help identify common ancestors and divergence points, leading to the construction of a phylogenetic tree.

Question 9

Q1: What does each branch on a phylogenetic tree represent?

Answer 9

• A1: Each branch represents the evolutionary pathway of a group of organisms, showing how they diverged from common ancestors over time.

Question 10

Q2: What is a sister group in a phylogenetic tree?

Answer 10

A2: A sister group consists of two species or groups that share a common ancestor not shared by any other group. For example, frogs and salamanders are sister groups because they share a common amphibian ancestor.

Question 11

Q3: What is the significance of nodes in a phylogenetic tree?

Answer 11

A3: Nodes represent points where a common ancestor diverged into two or more species or groups. The placement of a node reflects how recently species shared a common ancestor.

Question 12

Q4: How do we determine the closeness of evolutionary relationships between species in a phylogenetic tree?

Answer 12

A4: The closeness is determined by how recently two species shared a common ancestor. The more recent the common ancestor, the closer the evolutionary relationship between species.

Question 13

Q6: What kinds of data are used to construct phylogenetic trees?

Answer 13

A6: Phylogenetic trees are constructed using morphological data (physical features of organisms) and molecular data (genetic information). Both types of data help in understanding evolutionary relationships.

Question 14

Q7: What does Fig. 22.2 tell us about the evolutionary relationship between birds and crocodiles?

Answer 14

A7: The tree shows that birds and crocodiles share a recent common ancestor, making them closely related within the group of sauropsids.

Question 15

Q8: What is the significance of finding a node at a specific point in a phylogenetic tree?

Answer 15

A8: A node indicates a speciation event where one lineage split into two or more distinct species or groups. The location of the node helps scientists trace back evolutionary history to common ancestors.

Question 16

Q9: How can phylogenetic trees be used to refine evolutionary hypotheses?

Answer 16

• A9: By comparing morphological and molecular data, phylogenetic trees provide a visual hypothesis of evolutionary history. As new data is gathered, the tree can be adjusted to reflect more accurate evolutionary relationships.

Question 17

Q10: What is the purpose of grouping species in a phylogenetic tree based on shared characteristics?

Answer 17

• A10: Grouping species based on shared characteristics helps scientists trace evolutionary history and understand how certain traits evolved in different lineages. It also simplifies the representation of large amounts of species.

Question 18

1. What is the significance of nodes on a phylogenetic tree, and what do they represent about the species or groups being studied?

Answer 18

: Nodes on a phylogenetic tree represent common ancestors shared by the groups or species that diverge from that point. A node signifies a point where a single ancestral lineage splits into two or more descendant lineages, representing a speciation event.

Question 19

2. Why is it incorrect to think of a species on a phylogenetic tree as more ‘advanced’ than another species that diverged earlier?

Answer 19

• Answer: It’s incorrect to label species as ‘advanced’ because evolutionary trees do not represent progress or hierarchy. All species, regardless of when they branched off, are adapted to their specific environments. More recently evolved species are not necessarily more complex or superior; they are simply different.

Question 20

3. How can the structure of a phylogenetic tree help us understand evolutionary relationships without knowing every individual species within a group?

Answer 20

: The structure of a phylogenetic tree shows relationships based on common ancestry rather than the specifics of each species. By understanding how groups of species are related through common ancestors (represented by nodes), we can infer evolutionary relationships even if we don’t know every individual species.

Question 21

4. Explain why sister groups are important in phylogenetics. How do they help in understanding evolutionary relationships?

Answer 21

Answer: Sister groups are two species or groups that are more closely related to each other than to any other group because they share a more recent common ancestor. Identifying sister groups helps clarify evolutionary relationships and highlights which species have diverged from common ancestors most recently.

Question 22

5. Why can the branches of a phylogenetic tree be rotated without altering the evolutionary relationships between the species?

Answer 22

: The branches of a phylogenetic tree can be rotated around nodes because the relative positions of the species remain the same. The rotation doesn’t change the branching order, which determines the evolutionary relationships. It simply rearranges the visual representation without affecting the underlying data about common ancestors.

Question 23

6. What does the term ‘closeness of relationship’ mean in the context of a phylogenetic tree? How do we determine this?

Answer 23

• Answer: ‘Closeness of relationship’ refers to how recently two groups share a common ancestor. This is determined by the location of the nodes on the tree. The more recent the common ancestor, the closer the relationship. You trace this by following the branches from the tip of the tree back to the root.

Question 24

7. Why is it important to note that a phylogenetic tree is a hypothesis? What does this say about the nature of evolutionary study?

Answer 24

• Answer: A phylogenetic tree is a hypothesis because it represents the best model of evolutionary relationships based on available data, such as morphology or molecular traits. As new evidence emerges, these trees can change, showing that our understanding of evolutionary relationships is always evolving and subject to refinement.

Question 25

8. How does a phylogenetic tree represent both the evolutionary history of species and the relatedness of groups?

Answer 25

• Answer: A phylogenetic tree represents evolutionary history through its branching structure, showing how different species have diverged from common ancestors over time. The relatedness of groups is shown by how closely they branch off from one another, with more closely related species sharing more recent common ancestors.

Question 26

1. What is a monophyletic group, and why is it significant in evolutionary biology?

Answer 26

• A monophyletic group is a set of species or groups that includes an ancestor and all its descendants. It is significant because it helps in understanding evolutionary relationships based on a common ancestry, ensuring that all organisms in the group are biologically related.

Question 27

2. Explain the difference between a paraphyletic group and a polyphyletic group.

Answer 27

A paraphyletic group includes some but not all descendants of a common ancestor, while a polyphyletic group contains species from different ancestors, not including the most recent common ancestor.

Question 28

3. How does convergent evolution lead to the formation of polyphyletic groups?

Answer 28

Convergent evolution occurs when different species evolve similar traits independently, often due to similar environmental pressures. This can result in polyphyletic groups, where the organisms share traits but do not share a common ancestor for those traits (e.g., wings in birds and bats).

Question 29

4. What does a node represent in a phylogenetic tree, and why are nodes critical for understanding evolutionary relationships?

Answer 29

• A node represents a point where a single species diverges into two or more distinct groups. Nodes are critical because they signify common ancestors, allowing us to trace the evolutionary path and relationships between species.

Question 30

5. What are sister groups, and how are they identified in a phylogenetic tree?

Answer 30

• Sister groups are the closest relatives to each other in a phylogenetic tree. They are identified by tracing two lineages back to a shared common ancestor from which no other groups have descended.

Question 31

• Sister groups are the closest relatives to each other in a phylogenetic tree. They are identified by tracing two lineages back to a shared common ancestor from which no other groups have descended.

Answer 31

• The tetrapod group is monophyletic because all species within the group share a common ancestor, which is not shared with any other group. This classification is useful for understanding vertebrate evolution as it helps focus on the shared traits and evolutionary history of all four-limbed vertebrates.

Question 32

7. Why are birds and bats considered to form a polyphyletic group in relation to their wings?

Answer 32

• Birds and bats form a polyphyletic group because their wings are the result of convergent evolution, meaning their winged trait evolved separately in each lineage and not from a common winged ancestor.

Question 33

1. What is the significance of sister groups in phylogenetic trees?

Answer 33

• Answer: Sister groups are the closest relatives in a phylogenetic tree, sharing a more recent common ancestor with each other than with any other group. Identifying sister groups helps trace evolutionary relationships and common ancestry.

Question 34

2. Why is the group “fish” considered paraphyletic, and what is the evolutionary implication?

Answer 34

• Answer: The group “fish” is paraphyletic because it includes only some descendants of a common ancestor, excluding tetrapods (amphibians, reptiles, mammals). This classification implies that while all tetrapods evolved from fish, the exclusion of these groups leads to an incomplete representation of the fish lineage.

Question 35

3. In what way does convergent evolution lead to polyphyletic groups, and can you give an example?

Answer 35

• Answer: Convergent evolution occurs when different species evolve similar traits independently, leading to polyphyletic groups. An example is birds and bats, both having wings, but their last common ancestor did not possess wings. Thus, the wings evolved separately in both lineages.

Question 36

4. How does taxonomy serve as an information storage and retrieval system?

Answer 36

• Answer: Taxonomy organizes species into hierarchical categories based on evolutionary relationships, allowing scientists to communicate information about organisms and make predictions about their traits. This system helps store biological information and retrieve it efficiently when studying species.

Question 37

. What is the difference between a monophyletic and a polyphyletic group in terms of evolutionary history?

Answer 37

Answer: A monophyletic group includes all descendants of a single common ancestor, preserving the full evolutionary lineage. In contrast, a polyphyletic group includes organisms from different lineages that do not share a common ancestor, often grouped together due to similar traits that evolved independently.

Question 38

6. How do biologists use phylogenetic trees to test hypotheses about evolutionary relationships?

Answer 38

• Answer: Biologists construct phylogenetic trees based on morphological and genetic data. These trees are hypotheses about the evolutionary relationships between species. New data, especially molecular evidence, can confirm or refine these hypotheses, ensuring the tree represents the most accurate evolutionary pathways.

Question 39

7. What role do nodes play in understanding evolutionary divergence?

Answer 39

• Answer: Nodes represent the point where two lineages diverge from a common ancestor. The node’s position helps determine how recently two species share a common ancestor, with more recent nodes indicating closer evolutionary relationships.

Question 40

8. Why are birds and crocodiles considered sister groups, and what does this imply about their evolutionary history?

Answer 40

• Answer: Birds and crocodiles are considered sister groups because they share a common ancestor more recently with each other than with any other group, such as turtles. This relationship implies that they have more shared evolutionary traits and a closer lineage than either does with turtles.

Question 41

1. How can the concept of a paraphyletic group lead to misinterpretations in understanding evolutionary history?

Answer 41

Answer: A paraphyletic group excludes some descendants of a common ancestor, which can lead to the misinterpretation that the excluded groups are less evolved or unrelated, when in fact they share the same ancestral lineage.

Question 42

2. Why is it important for biologists to focus on monophyletic groups rather than polyphyletic groups in evolutionary studies?

Answer 42

• Answer: Monophyletic groups provide a more accurate reflection of evolutionary history because they include all descendants of a common ancestor, helping scientists track the full evolutionary pathway. Polyphyletic groups, by focusing on similar traits developed through convergent evolution, do not reflect shared ancestry and can obscure evolutionary relationships.

Question 43

3. How does taxonomy assist in predicting traits in unstudied organisms?

Answer 43

• Answer: Taxonomy groups organisms based on shared evolutionary history, so if organisms belong to a monophyletic group, scientists can predict that they may have inherited certain traits from their common ancestor, even if these traits have not yet been observed in all members of the group.

Question 44

4. What can be inferred about the evolutionary process when two species from distant branches of a phylogenetic tree share a similar trait?

Answer 44

• Answer: When two distantly related species share a similar trait, it often indicates convergent evolution, meaning that the trait evolved independently in response to similar environmental pressures, rather than being inherited from a common ancestor.

Question 45

5. How does rotating the branches of a phylogenetic tree around a node affect the interpretation of evolutionary relationships?

Answer 45

Answer: Rotating branches around a node does not change the evolutionary relationships because the node represents the common ancestor. The arrangement of species on either side of the node may appear different, but their relative evolutionary relationships remain the same.

Question 46

6. In what way does the structure of a phylogenetic tree reflect the timeline of evolutionary divergence?

Answer 46

• Answer: In a phylogenetic tree, the root represents the most ancient ancestor, and as the tree branches out, it reflects the timeline of evolutionary divergence. The closer two species are to each other on the tree (closer to a shared node), the more recently they diverged from a common ancestor.

Question 47

7. What role do fossils play in constructing phylogenetic trees, and how can their absence affect interpretations?

Answer 47

• Answer: Fossils provide direct evidence of extinct species and can help pinpoint when certain traits or species appeared. Without fossils, constructing accurate phylogenetic trees becomes more challenging because the evolutionary history of extinct species is harder to infer from living organisms alone.

Question 48

8. Why might two species that appear morphologically similar be placed in different branches of a phylogenetic tree?

Answer 48

• Answer: Two species may appear similar due to convergent evolution, where similar environmental pressures lead to similar adaptations. However, genetic analysis may reveal that they belong to different evolutionary lineages, placing them on separate branches of the phylogenetic tree.

Question 49

9. How do phylogenetic trees help in understanding the evolutionary significance of vestigial structures in organisms?

Answer 49

• Answer: Phylogenetic trees can show when a trait or structure was functional in a common ancestor and how it was reduced or lost in certain descendants. Vestigial structures can indicate a shared evolutionary past, even if the structure no longer serves a purpose in the current organism.

Question 50

10. What does the concept of “descent with modification” imply about the diversity of life, as shown in phylogenetic trees?

Answer 50

• Answer: “Descent with modification” implies that all species are connected through common ancestry, and as they diverge, they accumulate differences due to evolutionary pressures. Phylogenetic trees visually represent this process, showing how various life forms are related through shared ancestry but have diversified over time.

Question 51

1. Question: What is a monophyletic group, and why is it considered the most accurate representation of evolutionary history?

Answer 51

: A monophyletic group includes a single common ancestor and all of its descendants, representing a complete evolutionary lineage. It is considered the most accurate representation of evolutionary history because it accurately traces back to the shared origin of all species within the group. For example, mammals form a monophyletic group, as they all descend from a common ancestor that was also a mammal, including humans, whales, bats, and others.

Question 52

2. Question: Can you provide an example of a monophyletic group in a phylogenetic tree, and explain why it is considered monophyletic?

Answer 52

: One example of a monophyletic group is the class Amphibia, which includes frogs, salamanders, and caecilians. This group is monophyletic because all amphibians share a single common ancestor that is not shared by any other group. The group contains all descendants from that common ancestor, meaning no species are excluded.

Question 53

3. Question: What is a paraphyletic group, and how does it differ from a monophyletic group? Can you give a specific exampl

Answer 53

Answer: A paraphyletic group includes a common ancestor and some, but not all, of its descendants. This makes the group incomplete and inaccurate in representing full evolutionary history. For example, fish is often considered a paraphyletic group because it includes ray-finned fish and sharks but excludes tetrapods (like amphibians and mammals), even though tetrapods also descended from the same common ancestor. In contrast, a monophyletic group would include all descendants of a common ancestor.

Question 54

4. Question: Why is the classification of fish as a group often considered paraphyletic, and what would need to change to make it monophyletic?

Answer 54

Answer: The classification of fish is considered paraphyletic because it includes aquatic species like sharks and ray-finned fish but excludes tetrapods (such as mammals and reptiles), which also share a common ancestor with fish. To make the group monophyletic, the classification would need to include all descendants of that common ancestor, such as amphibians, reptiles, birds, and mammals, alongside fish.

Question 55

5. Question: What is a polyphyletic group, and how does it misrepresent evolutionary relationships? Provide an example that illustrates this.

Answer 55

Answer: A polyphyletic group is formed when species from different evolutionary lineages (without a recent common ancestor) are grouped together based on similar traits that arose independently, often due to convergent evolution. For instance, grouping bats and birds as “winged animals” creates a polyphyletic group because both developed wings independently through evolution, but they do not share a common ancestor with wings. This misrepresents their evolutionary relationships because wings are not inherited from a shared ancestor.

Question 56

6. Question: Can you explain why winged animals, including bats and birds, form a polyphyletic group, and how convergent evolution plays a role?

Answer 56

: Bats and birds form a polyphyletic group because, while they both have wings, they evolved them independently from different ancestors through a process called convergent evolution. The evolution of wings in bats and birds did not come from a common winged ancestor. Instead, each group adapted to flight in response to similar environmental pressures, but from different starting points in their evolutionary history.

Question 57

7. Question: How does a polyphyletic group differ from a paraphyletic group, and why are both considered less accurate than a monophyletic group in depicting evolutionary history?

Answer 57

: A polyphyletic group includes species from different evolutionary ancestors that do not share a common ancestor, while a paraphyletic group includes a common ancestor but excludes some descendants. Both are considered less accurate than a monophyletic group because they fail to represent the complete lineage from a single ancestor. A monophyletic group accurately includes a common ancestor and all its descendants, showing a full and complete evolutionary history.

Question 58

8. Question: Provide a detailed example of a monophyletic, paraphyletic, and polyphyletic group, and explain how they are different using these examples.

Answer 58

• A monophyletic group example is mammals, which include a common ancestor and all its descendants (such as humans, whales, and bats).
  
  • A paraphyletic group example is fish, which includes aquatic species like sharks and ray-finned fish but excludes tetrapods, despite tetrapods also descending from the same ancestor.
  • A polyphyletic group example is winged animals, including bats and birds, which evolved wings independently from different ancestors.
    These groups differ because monophyletic groups include the complete lineage, paraphyletic groups leave out some descendants, and polyphyletic groups do not share a common ancestor, grouping species based on traits that evolved independently.

Question 59

9. Question: Why are monophyletic groups preferred over paraphyletic and polyphyletic groups in modern taxonomy and systematics?

Answer 59

Answer: Monophyletic groups are preferred in modern taxonomy because they represent complete evolutionary lineages, including a common ancestor and all its descendants, making them accurate reflections of evolutionary history. In contrast, paraphyletic groups omit some descendants, and polyphyletic groups group species based on traits that evolved independently, both of which misrepresent evolutionary relationships

Question 60

10. Question: What evolutionary process often leads to the formation of polyphyletic groups, and how does this differ from the way monophyletic groups are formed?

Answer 60

Answer: Convergent evolution often leads to the formation of polyphyletic groups because it involves the independent evolution of similar traits (like wings in bats and birds) in species from different evolutionary lineages. In contrast, monophyletic groups are formed based on shared ancestry, where species inherit traits from a common ancestor. Monophyletic groups accurately reflect evolutionary history, while polyphyletic groups do not.

Question 61

1. Q: What is the difference between homology and analogy in evolutionary biology?

Answer 61

A: Homology refers to similarities that arise due to common ancestry, meaning the trait was inherited from a shared ancestor. Analogy, on the other hand, refers to similarities that arise independently in unrelated species due to convergent evolution, where similar traits develop as adaptations to similar environments.

Question 62

2. Q: Why are wings in bats and birds considered analogous traits rather than homologous traits?

Answer 62

A: The wings in bats and birds are analogous because they evolved independently in both groups as adaptations for flight. While they serve the same function, their underlying structure and evolutionary origins are different. Bats have wings supported by long fingers, while birds have wings supported by modified forelimbs.

Question 63

3. Q: How do biologists use shared derived characters to build a phylogenetic tree?

Answer 63

A: Shared derived characters, or synapomorphies, are traits that are unique to a specific group of organisms and were inherited from their most recent common ancestor. Biologists compare these characters among species to infer evolutionary relationships and construct a phylogenetic tree, grouping species that share more derived traits together.

Question 64

4. Q: What is a synapomorphy, and why is it important in cladistics?

Answer 64

• A: A synapomorphy is a derived character state that is shared by two or more taxa and inherited from their most recent common ancestor. It is important in cladistics because it helps biologists identify evolutionary relationships and construct a phylogenetic tree by grouping organisms that share these traits.

Question 65

5. Q: Why can’t all homologous traits be used to determine sister group relationships?

Answer 65

• A: Not all homologous traits are informative for determining sister group relationships because some traits evolved after a group diverged from its sister group. For example, while all bats have wings, this character cannot help identify the sister group to bats because wings evolved after bats diverged from other mammals.

Question 66

6. Q: Explain how convergent evolution can result in analogous traits.

Answer 66

• A: Convergent evolution occurs when different species evolve similar traits independently due to facing similar environmental challenges. For example, the spines on hedgehogs and tenrecs are analogous traits because both species evolved these structures separately as adaptations to similar environments, even though they are not closely related.

Question 67

7. Q: How can character states help in distinguishing between homologous and analogous traits?

Answer 67

• A: Character states can help distinguish between homologous and analogous traits by examining whether the trait is present in a common ancestor (homologous) or whether it evolved independently in different lineages (analogous). Homologous traits will be shared by species that are more closely related, while analogous traits will occur in unrelated species due to convergent evolution.

Question 68

8. Q: What role does convergent evolution play in misleading phylogenetic interpretations?

Answer 68

A: Convergent evolution can lead to misleading interpretations of phylogenetic trees because it results in analogous traits that resemble each other in function but do not indicate shared ancestry. These traits might suggest a closer evolutionary relationship than actually exists, requiring careful analysis of other traits and genetic evidence.

Question 69

Q: Define cladistics and explain its significance in modern taxonomy.

Answer 69

• A: Cladistics is a method of classifying organisms based on shared derived traits (synapomorphies) to determine evolutionary relationships. It is significant because it helps biologists create a more accurate representation of evolutionary history by focusing on the branching patterns of evolution and grouping species based on common ancestry.

Question 70

10. Q: What is the simplest tree in phylogenetics, and why is it favored?

Answer 70

• A: The simplest tree in phylogenetics is the one that requires the fewest evolutionary changes to explain the observed data (this is called parsimony). It is favored because it minimizes the number of assumptions and provides a straightforward explanation for the evolutionary relationships among species.

Question 71

1. Q: How can convergent evolution lead to the development of analogous traits, and why is it essential to distinguish these from homologous traits when constructing phylogenetic trees?

Answer 71

• A: Convergent evolution leads to the development of analogous traits when unrelated species evolve similar adaptations independently due to similar environmental pressures. For example, both bats and dolphins evolved echolocation independently. It’s crucial to distinguish analogous traits from homologous ones because analogous traits do not reflect common ancestry and can lead to incorrect conclusions about evolutionary relationships if they are assumed to be inherited from a common ancestor.

Question 72

2. Q: What are the roles of characters and character states in determining evolutionary relationships between species, and how can variations in character states affect the interpretation of phylogenetic trees?

Answer 72

• A: Characters are features or traits observed in organisms, such as petals in flowers or wings in animals. Character states are the variations of those characters (e.g., the shape or arrangement of petals). In phylogenetics, characters shared by multiple species indicate potential evolutionary relationships. If character states show significant variation between species, they can suggest different evolutionary paths. For example, lungs are a shared character state in tetrapods, but their absence in other fish provides key insights into evolutionary divergence.

Question 73

3. Q: Explain why the presence of an amniotic egg is considered a homology among mammals, birds, and reptiles, and how this character is used in constructing phylogenetic trees.

Answer 73

• A: The presence of an amniotic egg is a homology because it evolved in a common ancestor of mammals, birds, and reptiles (sauropsids). This trait is inherited from that common ancestor and shared among these groups, making it a derived character state (synapomorphy) for identifying evolutionary relationships. The presence of this shared trait helps biologists group these organisms together in a clade on a phylogenetic tree, distinguishing them from other animals that do not have amniotic eggs.

Question 74

4. Q: In what ways can synapomorphies (shared derived traits) provide evidence for grouping species into monophyletic groups? Provide an example.

Answer 74

• A: Synapomorphies provide evidence for grouping species into monophyletic groups by highlighting traits that were inherited from a recent common ancestor unique to that group. These traits define the group as distinct from others. For example, the presence of hair and mammary glands is a synapomorphy for mammals. This trait groups all mammals together, indicating that they share a more recent common ancestor with each other than with non-mammals.

Question 75

5. Q: Why might traits that evolved through convergent evolution (analogous traits) be misleading when constructing a phylogenetic tree, and how can this issue be resolved?

Answer 75

• A: Traits that evolved through convergent evolution, like the wings of bats and birds, can be misleading because they suggest a closer evolutionary relationship than exists. These analogous traits evolved independently and are not derived from a common ancestor, which can confuse the interpretation of evolutionary trees. This issue can be resolved by examining other traits and genetic data that clarify whether the species share deeper evolutionary connections.

Question 76

6. Q: How can biologists use the outgroup comparison method to infer the ancestral state of a character in a phylogenetic tree? Why is this important?

Answer 76

• A: In outgroup comparison, biologists use a species (the outgroup) that is outside the group of interest (the ingroup) to infer the ancestral state of a character. If the outgroup and some members of the ingroup share a character state, it is likely the ancestral state. This method is important because it helps establish the direction of evolutionary change and determine which character states are derived (synapomorphies) and which are ancestral.

Question 77

7. Q: Why are shared derived traits (synapomorphies) more informative for determining evolutionary relationships than ancestral traits? Provide an example to support your explanation.

Answer 77

• A: Synapomorphies are more informative for determining evolutionary relationships because they are newly evolved traits shared by a specific group, indicating a recent common ancestor. In contrast, ancestral traits are inherited from distant ancestors and may be present in many groups, making them less useful for distinguishing recent relationships. For example, having a backbone is an ancestral trait shared by all vertebrates, but having hair is a synapomorphy unique to mammals.

Question 78

8. Q: How does the concept of parsimony guide the construction of phylogenetic trees, and why is the simplest tree often preferred?

Answer 78

• A: Parsimony guides the construction of phylogenetic trees by favoring the tree that requires the fewest evolutionary changes to explain the observed traits. The simplest tree is preferred because it minimizes the number of assumptions and evolutionary events, providing a more straightforward and likely explanation for the relationships among species. For instance, if a character evolved once in a common ancestor, rather than independently in multiple lineages, this is considered more parsimonious.

Question 79

9. Q: What is a polyphyletic group, and why is it considered problematic in phylogenetic classification? Give an example of a polyphyletic group and explain why it is misleading.

Answer 79

• A: A polyphyletic group is a group of organisms that do not share a recent common ancestor but are grouped together based on similar traits that evolved independently (analogous traits). This is problematic because it does not accurately reflect evolutionary relationships. An example is grouping bats and birds together because they both have wings, despite their wings evolving independently. This grouping is misleading because it suggests they are closely related when, in fact, they are not.

Question 80

10. Q: How do synapomorphies (shared derived traits) differ from symplesiomorphies (shared ancestral traits), and how does each type of trait affect the grouping of species on a phylogenetic tree?

Answer 80

• A: Synapomorphies are derived traits shared by two or more species that indicate a recent common ancestor, whereas symplesiomorphies are ancestral traits shared by multiple species but inherited from a distant ancestor. Synapomorphies help define monophyletic groups by highlighting newly evolved traits specific to certain lineages. In contrast, symplesiomorphies may lead to grouping distantly related species together because these traits were inherited from ancient ancestors. For example, vertebrae are a symplesiomorphy among vertebrates, but hair is a synapomorphy for mammals.