Mechanisms of Evolution Ch. 25

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Assessment 1 Ch. 25
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1

What are examples of Macroevolutionary change

  • the emergence of terrestrial vertebrates through a series of speciation events
  • the impact of mass extinction on biodiversity
  • the origin of key adaptations such as flight
2

Radiometric dating

a method for determining the absolute age of rocks and fossils, based on the half-life of radioactive isotopes

3

Geologic record

A standard time scale dividing earth history into time periods, grouped into four Eons

  • Hadean
  • Archaean
  • Proterozoic
  • Phanerozoic
4

Which of the following factors weaken(s) the hypothesis of abiotic synthesis of organic monomers in early Earth's atmosphere?

1. the relatively short time between intense meteor bombardment and the appearance of the first life-forms
2. the lack of experimental evidence that organic monomers can form by abiotic synthesis
3. uncertainty about which gases comprised early Earth's atmosphere

1 and 3

5

How were conditions on the early Earth of more than 3 billion years ago different from those on today's Earth?

Only early Earth was intensely bombarded by large space debris.

6

What is true of the amino acids that might have been delivered to Earth within carbonaceous chondrites?

There were more kinds of amino acids on the chondrites than are found in living organisms today.

7

Which of the following is the correct sequence of events in the origin of life?

I. formation of protobionts
II. synthesis of organic monomers
III. synthesis of organic polymers
IV. formation of DNA-based genetic systems

II,III,I,IV

8

Which of the following is a defining characteristic that all protobionts had in common?

a surrounding membrane or membrane-like structure

9

The first genes on Earth were probably

auto-catalytic RNA molecules

10

The synthesis of new DNA requires the prior existence of oligonucleotides to serve as primers. On Earth, these primers are small RNA molecules. This latter observation is evidence in support of the hypothesized existence of

earlier genetic systems than those based on DNA.

11

Several scientific laboratories across the globe are involved in research concerning the origin of life on Earth. Which of these questions is currently the most problematic and would have the greatest impact on our understanding if we were able to answer it?

How did RNA sequences come to carry the code for amino acid sequences?

12

If natural selection in a particular environment favored genetic systems that permitted the production of daughter "cells" that were genetically dissimilar from the mother "cells," then one should expect selection for which of the following?

I. polynucleotide polymerase with low mismatch error rates
II. polynucleotide polymerases without proofreading capability
III. batteries of efficient polynucleotide repair enzymes
IV. polynucleotide polymerases with proofreading capability
V. polynucleotide polymerases with high mismatch error rates

II and V

13

If the half-life of carbon-14 is about 5,730 years, then a fossil that has one-sixteenth the normal proportion of carbon-14 to carbon-12 should be about how many years old?

22,900

14

Which measurement(s) would help determine absolute dates by radiometric means?

  • The accumulation of the daughter isotope
  • The loss of parent isotopes
15

Approximately how far back in time does the fossil record extend?

3.5 billion years

16

If a fossil is encased in a stratum of sedimentary rock without any strata of igneous rock (for example, lava, volcanic ash) nearby, then it should be

difficult to determine the absolute age of the fossil, because radiometric dating of sedimentary rock is less accurate than that of igneous rock.

17

An early consequence of the release of oxygen gas by plant and bacterial photosynthesis was to

cause iron in ocean water and terrestrial rocks to rust (oxidize).

18

Which of the following statements provides the strongest evidence that prokaryotes evolved before eukaryotes?

The oldest fossilized cells resemble prokaryotes.

19

What is true of the Cambrian explosion?

Recent evidence supports the contention that the Cambrian explosion may not have been as "explosive" as was once thought

20

What is thought to be the correct sequence of these events, from earliest to most recent, in the evolution of life on Earth?

1. origin of mitochondria
2. origin of multicellular eukaryotes
3. origin of chloroplasts
4. origin of cyanobacteria
5. origin of fungal-plant symbioses

4,1,3,2,5

21

If it were possible to conduct sophisticated microscopic and chemical analyses of microfossils found in 3.2-billion-year-old stromatolites, then one should be surprised to observe evidence of which of the following within such microfossils?

I. double-stranded DNA
II. a nuclear envelope
III. a nucleoid
IV. a nucleolus
V. ribosomes

II and IV

22

Recent evidence indicates that the first major diversification of multicellular eukaryotes may have coincided in time with the

melting that ended the "snowball Earth" period.

23

Which of these observations gives the most support to the endosymbiotic theory for the origin of eukaryotic cells?

the similarity in size between the cytosolic ribosomes of prokaryotes and the ribosomes within mitochondria and chloroplasts

24

Which event is nearest in time to the end of the period known as snowball Earth?

Cambrian explosion

25

The snowball Earth hypothesis provides a possible explanation for the

diversification of animals during the late Proterozoic era.

26

Which of the following characteristics should have been possessed by the first animals to colonize land?

1. were probably herbivores (ate photosynthesizers)
2. had four appendages
3. had the ability to resist dehydration
4. had lobe-finned fishes as ancestors
5. were invertebrates

1,3,5

27

The first terrestrial organisms probably were considered which of the following?

1. burrowers
2. photosynthetic
3. multicellular
4. prokaryotes
5. eukaryotes
6. plants and their associated fungi

2 and 4

28

If two continents converge and are united, then the collision should cause

a net loss of intertidal zone and coastal habitat.

29

The major evolutionary episode corresponding most closely in time with the formation of Pangaea was the

Permian extinctions.

30

On the basis of their morphologies, how might Linnaeus have classified the Hawaiian silverswords?

He would have placed them in more species than modern botanists do.

31

An organism has a relatively large number of Hox genes in its genome. Which of the following is true of this organism?

The organism has the genetic potential to have a relatively complex anatomy.

32

Bagworm moth caterpillars feed on evergreens and carry a silken case or bag around with them in which they eventually pupate. Adult female bagworm moths are larval in appearance; they lack the wings and other structures of the adult male and instead retain the appearance of a caterpillar even though they are sexually mature and can lay eggs within the bag. This is a good example of

paedomorphosis.

33

The loss of ventral spines by modern freshwater sticklebacks is due to natural selection operating on the phenotypic effects of Pitx1 gene

silencing (loss of expression).

34

Larval flies (maggots) express the Ubx gene in all of their segments, and thereby lack appendages. If this same gene continued to be expressed throughout subsequent developmental stages, except in the head region, and if the result was a fit, sexually mature organism that still strongly resembled a maggot, this would be an example of

Heterochrony

Paedomorphisis

35

How many of the following statements concerning the loss of hind limbs during whale evolution are true?

1. It is well documented by a series of transitional fossils.
2. It explains why modern whales have vestigial pelvic girdles.
3. It involved changes in the sequence or expression of Hox genes.
4. It is an example of macroevolution.
5. It, and the loss of limbs by snakes, are an example of similar adaptations to a similar environment.

All five statements are true.

36

The existence of the phenomenon of exaptation is most closely associated with which of the following observations that natural selection cannot fashion perfect organisms?

Evolution is limited by historical constraints.

37

One explanation for the evolution of insect wings suggests that wings began as lateral extensions of the body that were used as heat dissipaters for thermoregulation. When they had become sufficiently large, these extensions became useful for gliding through the air, and selection later refined them as flight-producing wings. If this hypothesis is correct, modern insect wings could best be described as

exaptations.

38

if one organ is an exaptation of another organ, then what must be true of these two organs?

They are both homologous organs.

39

Many species of snakes lay eggs. However, in the forests of northern Minnesota where growing seasons are short, only live-bearing snake species are present. This trend toward species that perform live birth in a particular environment is an example of

species selection.

40

In the 5-7 million years that the hominid lineage has been diverging from its common ancestor with the great apes, dozens of hominid species have arisen, often with several species coexisting in time and space. As recently as 30,000 years ago, Homo sapiens coexisted with Homo neanderthalensis. Both species had large brains and advanced intellects. The fact that these traits were common to both species is most easily explained by which of the following?

species selection

41

The existence of evolutionary trends, such as increasing body sizes among horse species, is evidence that

in particular environments, similar adaptations can be beneficial in more than one species.

42

Fossil evidence indicates that several kinds of flightless dinosaurs possessed feathers. If some of these feather-bearing dinosaurs incubated clutches of eggs in carefully constructed nests, this might be evidence supporting the claim that

their feathers originally served as insulation, and only later became flight surfaces.

43
card image

Several scientific laboratories across the globe are involved in research concerning the origin of life on Earth. Which graph below, if the results were produced abiotically, would have the greatest promise for revealing important information about the origin of Earth's first genetic system?

B

44
card image

The figure represents a cross-section of the seafloor through a mid-ocean rift valley, with alternating patches of black and white indicating seafloor with reversed magnetic polarities. At the arrow labeled "I" (the rift valley), the igneous rock of the seafloor is so young that it can be accurately dated using carbon-14 dating. At the arrow labeled "III," however, the igneous rock is about 1 million years old, and potassium-40 dating is typically used to date such rocks. Note: The horizontal arrows indicate the direction of sea-floor spreading, away from the rift valley.

Assuming that the rate of sea-floor spreading was constant during the 1-million-year period depicted above, Earth's magnetic field has undergone reversal at an average rate of once every

250,000 years

45
card image

The figure represents a cross section of the sea floor through a mid-ocean rift valley, with alternating patches of black and white indicating sea floor with reversed magnetic polarities. At the arrow labeled "I" (the rift valley), the igneous rock of the sea floor is so young that it can be accurately dated using carbon-14 dating. At the arrow labeled "III," however, the igneous rock is about 1 million years old, and potassium-40 dating is typically used to date such rocks. Note: The horizontal arrows indicate the direction of sea-floor spreading, away from the rift valley.

Which section of sea-floor crust should have the thickest layer of overlying sediment, assuming a continuous rate of sediment

E

46
card image

The figure represents a cross section of the sea floor through a mid-ocean rift valley, with alternating patches of black and white indicating sea floor with reversed magnetic polarities. At the arrow labeled "I" (the rift valley), the igneous rock of the sea floor is so young that it can be accurately dated using carbon-14 dating. At the arrow labeled "III," however, the igneous rock is about 1 million years old, and potassium-40 dating is typically used to date such rocks. Note: The horizontal arrows indicate the direction of sea-floor spreading, away from the rift valley.

If a particular marine organism is fossilized in the sediments immediately overlying the igneous rock at the arrow labeled "II," at which other location, labeled A—E, would a search be most likely to find more fossils of this organism?

C only

47
card image

The figure represents a cross section of the sea floor through a mid-ocean rift valley, with alternating patches of black and white indicating sea floor with reversed magnetic polarities. At the arrow labeled "I" (the rift valley), the igneous rock of the sea floor is so young that it can be accurately dated using carbon-14 dating. At the arrow labeled "III," however, the igneous rock is about 1 million years old, and potassium-40 dating is typically used to date such rocks. Note: The horizontal arrows indicate the direction of sea-floor spreading, away from the rift valley.

How many other bands of sea-floor crust in Figure 25.1 have the same magnetic polarity as the crust that directly straddles the rift valley?

four bands

48
card image

The figure represents a cross section of the sea floor through a mid-ocean rift valley, with alternating patches of black and white indicating sea floor with reversed magnetic polarities. At the arrow labeled "I" (the rift valley), the igneous rock of the sea floor is so young that it can be accurately dated using carbon-14 dating. At the arrow labeled "III," however, the igneous rock is about 1 million years old, and potassium-40 dating is typically used to date such rocks. Note: The horizontal arrows indicate the direction of sea-floor spreading, away from the rift valley.

Assuming that the rate of sea-floor spreading was constant during the 1-million-year period depicted above, what should be the approximate age of marine fossils found in undisturbed sedimentary rock immediately overlying the igneous rock at the arrow labeled "II"?

400,000 years

49
card image

A sediment core is removed from the floor of an inland sea. The sea has been in existence, off and on, throughout the entire time that terrestrial life has existed. Researchers wish to locate and study the terrestrial organisms fossilized in this core. The core is illustrated as a vertical column, with the top of the column representing the most recent strata and the bottom representing the time when land was first colonized by life.

If arrows indicate locations in the column where fossils of a particular type (see key above) first appear, then which core in Figure 25.2 has the most accurate arrangement of fossils?

Core A

50
card image

A sediment core is removed from the floor of an inland sea. The sea has been in existence, off and on, throughout the entire time that terrestrial life has existed. Researchers wish to locate and study the terrestrial organisms fossilized in this core. The core is illustrated as a vertical column, with the top of the column representing the most recent strata and the bottom representing the time when land was first colonized by life.

Which of the following reasons may explain why the sediment core lacks fossils of dragonflies with 3-feet wingspans?

1. This particular sediment core includes the correct stratum, but the part of the stratum captured by the core lacks such fossils.
2. The sea was not present at this site during the time that 3-feet dragonflies existed.
3. Dragonflies have no hard parts, such as exoskeletons, to fossilize.
4. The sediments containing these fossils at this site may have been eroded away during a time when the sea had receded from this site.
5. Dragonflies are terrestrial; therefore, fossils of terrestrial organisms should not be expected in the sediments of seas.

1,2, or 4

51

In order to properly interpret sediment cores, it is necessary to apply the principle of

superposition.

52

Assuming the existence of fossilized markers for each of the following chemicals, what is the sequence in which they should be found in this sediment core, working from ancient sediments to recent sediments?

1. chitin coupled with protein
2. chlorophyll
3. bone
4. cellulose

2,4,1,3

53

In order to assign absolute dates to fossils in this sediment core, it would be most helpful if

volcanic ash layers were regularly interspersed between the sedimentary strata.

54
card image

According to the theory of sea-floor spreading, oceanic islands, such as the Hawaiian Islands depicted in Figure 25.3, form as oceanic crustal plates move over a stationary "hot spot" in the mantle. Currently, the big island of Hawaii is thought to be over a hot spot, which is why it is the only one of the seven islands that has active volcanoes. What should be true of the island of Hawaii?

1. Scientists in search of ongoing speciation events are more likely to find them here than on the other six islands.
2. Its species should be more closely related to those of nearer islands than to those of farther islands.
3. It should have a rich fossil record of terrestrial organisms.
4. There is a good chance of finding endemic species on this island.
5. On average, it should have fewer species per unit surface area than the other six islands

1,2,4 and 5

55
card image

Hawaii is the most southeastern of the seven islands and is also closest to the sea-floor spreading center from which the Pacific plate originates, which lies about 5,600 km further to the southeast. Assuming equal sedimentation rates, what should be the location of the thickest sediment layer and, thus, the area with the greatest diversity of fossils above the oceanic crust?

around the base of Kauai, the oldest of the Hawaiian islands

56
card image

Soon after the island of Hawaii rose above the sea surface (somewhat less than 1 million years ago), the evolution of life on this new island should have been most strong

founder effect.

57
card image

Upon being formed, oceanic islands, such as the Hawaiian Islands, should feature what characteristic, leading to which phenomenon?

a variety of empty ecological niches, leading to adaptive radiation

58

Fossils of Lystrosaurus, a dicynodont therapsid, are most common in parts of modern-day South America, South Africa, Madagascar, India, South Australia, and Antarctica. It apparently lived in arid regions, and was mostly herbivorous. It originated during the mid-Permian period, survived the Permian extinction, and dwindled by the late Triassic, though there is evidence of a relict population in Australia during the Cretaceous period. The dicynodonts had two large tusks, extending down from their upper jaws. The tusks were not used for food gathering, and in some species were limited to males. Food was gathered using an otherwise toothless beak. Judging from the fossil record in sedimentary rocks, these pig-sized organisms were the most common mammal-like reptiles of the Permian.

Anatomically, what was true of Lystrosaurus?

It was a tetrapod.

59

Fossils of Lystrosaurus, a dicynodont therapsid, are most common in parts of modern-day South America, South Africa, Madagascar, India, South Australia, and Antarctica. It apparently lived in arid regions, and was mostly herbivorous. It originated during the mid-Permian period, survived the Permian extinction, and dwindled by the late Triassic, though there is evidence of a relict population in Australia during the Cretaceous period. The dicynodonts had two large tusks, extending down from their upper jaws. The tusks were not used for food gathering, and in some species were limited to males. Food was gathered using an otherwise toothless beak. Judging from the fossil record in sedimentary rocks, these pig-sized organisms were the most common mammal-like reptiles of the Permian.

How many of Lystrosaurus' features below can help explain why these organisms fossilized so abundantly?

I. the presence of hard parts, such as tusks
II. its arid environment
III.its persistence across at least two geological eras
IV. its widespread geographic distribution
V. its mixture of reptilian and mammalian features

Three Statements

60

Fossils of Lystrosaurus, a dicynodont therapsid, are most common in parts of modern-day South America, South Africa, Madagascar, India, South Australia, and Antarctica. It apparently lived in arid regions, and was mostly herbivorous. It originated during the mid-Permian period, survived the Permian extinction, and dwindled by the late Triassic, though there is evidence of a relict population in Australia during the Cretaceous period. The dicynodonts had two large tusks, extending down from their upper jaws. The tusks were not used for food gathering, and in some species were limited to males. Food was gathered using an otherwise toothless beak. Judging from the fossil record in sedimentary rocks, these pig-sized organisms were the most common mammal-like reptiles of the Permian.

Which of the following is the most likely explanation for the modern-day distribution of dicynodont fossils?

The dicynodonts were distributed more abundantly throughout Gondwanaland than throughout any other land mass.

61

Fossils of Lystrosaurus, a dicynodont therapsid, are most common in parts of modern-day South America, South Africa, Madagascar, India, South Australia, and Antarctica. It apparently lived in arid regions, and was mostly herbivorous. It originated during the mid-Permian period, survived the Permian extinction, and dwindled by the late Triassic, though there is evidence of a relict population in Australia during the Cretaceous period. The dicynodonts had two large tusks, extending down from their upper jaws. The tusks were not used for food gathering, and in some species were limited to males. Food was gathered using an otherwise toothless beak. Judging from the fossil record in sedimentary rocks, these pig-sized organisms were the most common mammal-like reptiles of the Permian.

If an increase in dicynodont species diversity (in other words, number of species) occurred soon after the Permian extinction, and if it occurred for the same general reason usually given for the increase in mammalian diversity following the Cretaceous extinction, then it should be attributed to

the availability of previously occupied niches.

62

The following question is based on the observation that several dozen different proteins comprise the prokaryotic flagellum and its attachment to the prokaryotic cell, producing a highly complex structure.

If the complex protein assemblage of the prokaryotic flagellum arose by the same general processes as those of the complex eyes of molluscs (such as squids and octopi), then

ancestral versions of this protein assemblage were either less functional or had different functions than modern prokaryotic flagella.

63

The following question is based on the observation that several dozen different proteins comprise the prokaryotic flagellum and its attachment to the prokaryotic cell, producing a highly complex structure.

Certain proteins of the complex motor that drives bacterial flagella are modified versions of proteins that had previously belonged to plasma membrane pumps. This evidence supports the claim that

natural selection can produce new structures by coupling together parts of other structures.

64

A female fly, full of fertilized eggs, is swept by high winds to an island far out to sea. She is the first fly to arrive on this island, and the only fly to arrive in this way. Thousands of years later, her numerous offspring occupy the island, but none of them resembles her. There are, instead, several species, each of which eats only a certain type of food. None of the species can fly, for their flight wings are absent, and their balancing organs (in other words, halteres) are now used in courtship displays. The male members of each species bear modified halteres that are unique in appearance to their species. Females bear vestigial halteres. The ranges of all of the daughter species overlap.

If these fly species lost the ability to fly independently of each other as a result of separate mutation events in each lineage, then the flightless condition in these species could be an example of

species selection.

65

A female fly, full of fertilized eggs, is swept by high winds to an island far out to sea. She is the first fly to arrive on this island, and the only fly to arrive in this way. Thousands of years later, her numerous offspring occupy the island, but none of them resembles her. There are, instead, several species, each of which eats only a certain type of food. None of the species can fly, for their flight wings are absent, and their balancing organs (in other words, halteres) are now used in courtship displays. The male members of each species bear modified halteres that are unique in appearance to their species. Females bear vestigial halteres. The ranges of all of the daughter species overlap.

In each fly species, the entire body segment that gave rise to the original flight wings is missing. The mutation(s) that led to the flightless condition could have
A) duplicated all of the Hox genes in these flies' genomes.

  • Duplicated all of the Hox genes in these flies' genomes.
  • Altered the nucleotide sequence within a Hox gene.
  • Altered the expression of a Hox gene.
  • two of the above answers are correct
66

A female fly, full of fertilized eggs, is swept by high winds to an island far out to sea. She is the first fly to arrive on this island, and the only fly to arrive in this way. Thousands of years later, her numerous offspring occupy the island, but none of them resembles her. There are, instead, several species, each of which eats only a certain type of food. None of the species can fly, for their flight wings are absent, and their balancing organs (in other words, halteres) are now used in courtship displays. The male members of each species bear modified halteres that are unique in appearance to their species. Females bear vestigial halteres. The ranges of all of the daughter species overlap.

Fly species W, found in a certain part of the island, produces fertile offspring with species Y. Species W does not produce fertile offspring with species X or Z. If no other species can hybridize, then species W and Y

A) have genomes that are still similar enough for successful meiosis to occur in hybrid flies.
B) have more genetic similarity with each other than either did with the other two species.
C) may fuse into a single species if their hybrids remain fertile over the course of many generations.

67

A female fly, full of fertilized eggs, is swept by high winds to an island far out to sea. She is the first fly to arrive on this island, and the only fly to arrive in this way. Thousands of years later, her numerous offspring occupy the island, but none of them resembles her. There are, instead, several species, each of which eats only a certain type of food. None of the species can fly, for their flight wings are absent, and their balancing organs (in other words, halteres) are now used in courtship displays. The male members of each species bear modified halteres that are unique in appearance to their species. Females bear vestigial halteres. The ranges of all of the daughter species overlap.

Which of these fly organs, as they exist in current fly populations, best fits the description of an exaptation?

balancing organs

68

All animals with eyes or eyespots that have been studied so far share a gene in common. When mutated, the gene Pax-6 causes lack of eyes in fruit flies, tiny eyes in mice, and missing irises (and other eye parts) in humans. The sequence of Pax-6 in humans and mice is identical. There are so few sequence differences with fruit fly Pax-6 that the human/mouse version can cause eye formation in eyeless fruit flies, even though vertebrates and invertebrates last shared a common ancestor more than 500 million years ago.

The appearance of Pax-6 in all animals with eyes can be explained in multiple ways. Based on the information above, which explanation is most likely?

The Pax-6 gene was an innovation of an ancestral animal of the early Cambrian period. Animals with eyes or eyespots are descendants of this ancestor.

69

All animals with eyes or eyespots that have been studied so far share a gene in common. When mutated, the gene Pax-6 causes lack of eyes in fruit flies, tiny eyes in mice, and missing irises (and other eye parts) in humans. The sequence of Pax-6 in humans and mice is identical. There are so few sequence differences with fruit fly Pax-6 that the human/mouse version can cause eye formation in eyeless fruit flies, even though vertebrates and invertebrates last shared a common ancestor more than 500 million years ago.

Fruit fly eyes are of the compound type, which is structurally very different from the camera-type eyes of mammals. Even the camera-type eyes of molluscs, such as octopi, are structurally quite different from those of mammals. Yet, fruit flies, octopi, and mammals possess very similar versions of Pax-6. The fact that the same gene helps produce very different types of eyes is most likely due to

differences in the control of Pax-6 expression among these organisms.

70

All animals with eyes or eyespots that have been studied so far share a gene in common. When mutated, the gene Pax-6 causes lack of eyes in fruit flies, tiny eyes in mice, and missing irises (and other eye parts) in humans. The sequence of Pax-6 in humans and mice is identical. There are so few sequence differences with fruit fly Pax-6 that the human/mouse version can cause eye formation in eyeless fruit flies, even though vertebrates and invertebrates last shared a common ancestor more than 500 million years ago.

Pax-6 usually causes the production of a type of light-receptor pigment. In vertebrate eyes, though, a different gene (the rh gene family) is responsible for the light-receptor pigments of the retina. The rh gene, like Pax-6, is ancient. In the marine ragworm, for example, the rh gene causes production of c-opsin, which helps regulate the worm's biological clock. Which of these most likely accounts for vertebrate vision?

During vertebrate evolution, the rh gene for biological clock opsin was co-opted as a gene for visual receptor pigments.

71

Fossilized stromatolites

resemble structures formed by bacterial communities that are found today in some warm, shallow, salty bays.

72

The oxygen revolution changed Earth's environment dramatically. Which of the following took advantage of the presence of free oxygen in the oceans and atmosphere?

the evolution of cellular respiration, which used oxygen to help harvest energy from organic molecules

73

Which factor most likely caused animals and plants in India to differ greatly from species in nearby southeast Asia?

India was a separate continent until 45 million years ago.

74

Adaptive radiations can be a direct consequence of four of the following five factors. Select the exception

genetic drift

75

Which of the following steps has not yet been accomplished by scientists studying the origin of life?

formation of protocells that use DNA to direct the polymerization of amino acids

76

A genetic change that caused a certain Hox gene to be expressed along the tip of a vertebrate limb bud instead of farther back helped make possible the evolution of the tetrapod limb. This type of change is illustrative of

a change in a developmental gene or its regulation that altered the spatial organization of body parts.

77

A swim bladder is a gas-filled sac that helps fish maintain buoyancy. The evolution of the swim bladder from lungs of an ancestral fish is an example of

exaptation.