Origins Of Speicies And History Of Life On Earth Flashcards
(118 cards)
1
Q
Non-living; referring to the physical and chemical properties of an environment.
A
Abiotic
2
Q
The formation of new species in populations that are geographically isolated from one another.
A
Allopathic speciation
3
Q
Similarity between two species that is due to convergent evolution rather than to descent from a common ancestor with the same trait.
A
Analogy
4
Q
In a specified group of organisms, a taxon whose evolutionary lineage diverged early in the history of the group.
A
Basal taxon
5
Q
The two-part, latinized format for naming a species, consisting of the genus and specific epithet.
A
Binomial
6
Q
Definition of a species as a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but do not produce viable, fertile offspring with members of other such groups.
A
Biological species concept
7
Q
The representation on a phylogenetic tree of the divergence of two or more taxa from a common ancestor; usually shown as a dichotomy in which a branch representing the ancestral lineage splits into two parts, one for each of the two descendant lineages.
A
Branch point
8
Q
A relatively brief time in geologic history when many present-day phyla of animals first appeared in the fossil record. This burst of evolutionary change occurred about 535-525 million years ago and saw the emergence of the first large, hard-bodied animals.
A
Cambrian explosion
9
Q
An approach to systematics in which organisms are placed into groups called clades based primarily on common descent.
A
Cladistics
10
Q
A group of species that includes an ancestral species and all of its descendants.
A
Clade
11
Q
In Linnaean classification, the taxonomic category above the level of order.
A
Class
12
Q
(1) A deficiency in a chromosome resulting from the loss of a fragment through breakage. (2) A mutational loss of one or more nucleotide pairs from a gene.
A
Deletion
13
Q
A definition of species in terms of ecological niche, the sum of how members of the species interact with the non-living and living parts of their environment.
A
Ecological species
14
Q
The theory that mitochondria and plastids, including chloroplasts, originated as prokaryotic cells engulfed by an ancestral eukaryotic cell. The engulfed cell and its host cell then evolved into a single organism.
A
Endosymbiont theory
15
Q
A process in which a unicellular organism (the “host”) engulfs another cell, which lives within the host cell and ultimately becomes an organelle in the host cell.
A
Endosymbiosis
16
Q
Evolutionary developmental biology; a field of biology that compares developmental processes of different multicellular organisms to understand how these processes have evolved and how changes can modify existing organismal features or lead to new ones.
A
Evo-devo
17
Q
The division of Earth’s history into time periods, grouped into three eons – Archaean, Proterozoic, and Phanerozoic – and further subdivided into eras, periods, and epochs.
A
Geologic record
18
Q
The amount of time it takes for 50% of a sample of a radioactive isotope to decay.
A
Half-life
19
Q
Evolutionary change in the timing or rate of an organism’s development.
A
Heterochrony
20
Q
An organism that obtains organic food molecules by eating other organisms or substances derived from them.
A
Heterotroph
21
Q
Any of the master regulatory genes that control placement and spatial organization of body parts in animals, plants, and fungi by controlling the developmental fate of groups of cells.
A
Homeotic gene
22
Q
A similar (analogous) structure or molecular sequence that has evolved independently in two species.
A
Homoplasy
23
Q
Offspring that results from the mating of individuals from two different species or from two true-breeding varieties of the same species.
A
Hybrid
24
Q
A geographic region in which members of different species meet and mate, producing at least some offspring of mixed ancestry.
A
Hybrid zone
25
A mutation involving the addition of one or more nucleotide pairs to a gene.
Insertion
26
Evolutionary change above the species level. Examples of change include the origin of a new group of organisms through a series of speciation events and the impact of mass extinctions on the diversity of life and its subsequent recovery.
Macroevolution
27
The elimination of a large number of species throughout Earth, the result of global environmental changes.
Mass extinction
28
As applied to molecular systematics, a principle that states that when considering multiple phylogenetic hypotheses, one should take into account the hypothesis that reflects the most likely sequence of evolutionary events, given certain rules about how DNA changes over time.
Maximum likelihood
29
A principle that states that when considering multiple explanations for an observation, one should first investigate the simplest explanation that is consistent with the facts.
Maximum parsimony
30
A modified type of cell division in sexually reproducing organisms consisting of two rounds of cell division but only one round of DNA replication. It results in cells with half the number of chromosome sets as the original cell.
Meiosis
31
A process of nuclear division in eukaryotic cells conventionally divided into five stages: prophase, prometaphase, metaphase, anaphase, and telophase – conserves chromosome number by allocating replicated chromosomes equally to each of the daughter nuclei.
Mitosis
32
A scientific discipline that uses nucleic acids or other molecules to infer evolutionary relationships between different species.
Molecular systematics
33
Pertaining to a group of taxa that consists of a common ancestor and all of its descendants – this type of taxon is equivalent to a clade.
Monophyletic
34
A definition of species in terms of measurable anatomical criteria.
morphological species concept
35
In Linnaean classification, the taxonomic category above the level of family.
Order
36
Homologous genes that are found in different species because of speciation.
Orthologous genes
37
A species or group of species from an evolutionary lineage that is known to have diverged before the lineage that contains the group of species being studied; is selected so that its members are closely related to the group of species being studied, but not as closely related as any study- group members are to each other.
Outgroup
38
Homologous genes that are found in the same genome as a result of gene duplication.
Paralogous genes
39
Pertaining to a group of taxa that consists of a common ancestor and some, but not all, of its descendants.
Paraphyletic
40
Proposed system of classification of organisms based on evolutionary relationships: Only groups that include a common ancestor and all of its descendants are named.
PhyloCode
41
A definition of species as the smallest group of individuals that share a common ancestor, forming one branch on the tree of life.
phylogenetic species concept
42
A branching diagram that represents a hypothesis about the evolutionary history of a group of organisms.
phylogenetic tree
43
The evolutionary history of a species or group of related species.
phylogeny
44
In Linnaean classification, the taxonomic category above class.
phylum
45
The theory that the continents are part of great plates of Earth’s crust that float on the hot, underlying portion of the mantle. Movements in the mantle cause the continents to move slowly over time.
plate tectonics
46
Pertaining to a group of taxa derived from two or more different ancestors.
polyphyletic
47
A chromosomal alteration in which the organism possesses more than two complete chromosome sets. It is the result of an accident of cell division.
polyploidy
48
In a phylogenetic tree, a branch point from which more than two descendant taxa emerge; indicates that the evolutionary relationships between the descendant taxa are not yet clear.
polytomy
49
An abiotic precursor of a living cell that had a membrane-like structure and that maintained an internal chemistry different from that of its surroundings.
protocell
50
In the fossil record, long periods of apparent stasis, in which a species undergoes little or no morphological change, interrupted by relatively brief periods of sudden change.
punctuated equilibria
51
A method for determining the absolute age of rocks and fossils, based on the half-life of radioactive isotopes.
radiometric dating
52
The existence of biological factors (barriers) that impede members of two species from producing viable, fertile offspring.
reproductive isolation
53
RNA molecules that, together with proteins, make up ribosomes; the most abundant type of RNA.
ribosomal RNA (rRNA)
54
Describing a phylogenetic tree that contains a branch point (often, the one farthest to the left) representing the most recent common ancestor of all taxa in the tree.
rooted
55
A form of selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates.
sexual selection
56
A character, shared by members of a particular clade, that originated in an ancestor that is not a member of that clade.
shared ancestral character
57
An evolutionary novelty that is unique to a particular clade.
shared derived character
58
Groups of organisms that share an immediate common ancestor and hence are each other’s closest relatives.
sister taxa
59
An evolutionary process in which one species splits into two or more species.
speciation
60
A population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but do not produce viable, fertile offspring with members of other such groups.
species
61
Layered rock that results from the activities of prokaryotes that bind thin films of sediment together.
stromatolite
62
The formation of new species in populations that live in the same geographic area.
sympatric speciation
63
A scientific discipline focused on classifying organisms and determining their evolutionary relationships.
systematics
64
A named taxonomic unit at any given level of classification.
taxon
65
The diploid cell produced by the union of haploid gametes during fertilization; a fertilized egg.
zygote
66
A vertebrate clade whose members have limbs with digits – includes mammals, amphibians, and birds and other reptiles.
tetrapod
67
Concept 3.1 The biological ___(a)___ concept emphasizes reproductive ___(b)___.
(a) species
(b) isolation
68
Concept 3.2 ___(a)___ may take place with or without geographic ___(b)___.
(a) Speciation
(b) separation
69
Concept 3.3 Speciation may occur ___(a)___ and can result from changes in few or many ___(b)___.
(a) rapidly or slowly
(b) genes
70
Concept 3.4 ___(a)___ on early Earth made the ___(b)___ of life possible.
(a) Conditions
(b) history
71
Concept 3.6 Key events in life’s history include the origins of ___(a)___ organisms and the ___(b)___ of land.
(a) single-celled and multi-celled
(b) colonization
72
Concept 3.8 Major changes in body form can result from changes in the ___(a)___ and ___(b)___ of developmental genes.
(a) sequences
(b) regulation
73
Concept 3.7 The rise and fall of groups of organisms reflect differences in ___(a)___ and ___(b)___ rates.
(a) speciation
(b) extinction
74
Concept 3.9 ___(a)___ is not ___(b)___ oriented.
(a) Evolution
(b) goal
75
Concept 4.1 ___(a)___ illustrate evolutionary ___(b)___.
(a) Phylogenies
(b) relationships
76
Concept 4.2 ___(a)___ are ___(b)___ from morphological and molecular data.
(a) Phylogenies
(b) inferred
77
Concept 4.3 Shared ___(a)___ are used to construct ___(b)___ trees.
(a) characters
(b) phylogenetic
78
Concept 4.4 An organism’s evolutionary ___(a)___ is documented in its ___(b)___.
(a) history
(b) genome
79
Concept 4.5 New ___(a)___ continues to ___(b)___ our understanding of the tree of life.
(a) information
(b) revise
80
Which species concept is currently most popular among most biologists?
A. phylogenetic.
B. ecological.
C. biological.
D. morphological. E. generational.
A.
81
What was the species concept most used by Linnaeus?
A. biological.
B. generational.
C. morphological.
D. ecological.
E. phylogenetic.
C.
82
Two species of frogs belonging to the same genus occasionally mate, but the offspring fail to develop and hatch. What is the mechanism for keeping the two frog species separate?
A. the postzygotic barrier called hybrid inviability.
B. the postzygotic barrier called hybrid breakdown.
C. the prezygotic barrier called hybrid sterility.
D. gametic isolation.
E. adaptation.
A.
83
The biological species concept is inadequate for grouping A. plants.
B. parasites.
C. asexual organisms.
D. animals that migrate. E. sympatric populations.
C.
84
The difference between geographic isolation and habitat differentiation is the
A. relative locations of two populations as speciation occurs.
B. speed (tempo) at which two populations undergo speciation.
C. amount of genetic variation that occurs among two gene pools as speciation
occurs.
D. identity of the phylogenetic kingdom or domain in which these phenomena
occur.
E. the ploidy of the two populations as speciation occurs.
A.
85
Among known plant species, which of these have been the two most commonly occurring phenomena leading to the origin of new species? 1. allopatric speciation; 2. sympatric speciation; 3. sexual selection; 4. Polyploidy.
A. 1 and 3.
B. 1and4.
C. 2and3.
D. 2and4.
E. None of these.
D.
86
Beetle pollinators of a particular plant are attracted to its flowersʹ bright orange colour. The beetles not only pollinate the flowers, but they mate while inside of the flowers. A mutant version of the plant with red flowers becomes more common with the passage of time. A particular variant of the beetle prefers the red flowers to the orange flowers. Over time, these two beetle variants diverge from each other to such an extent that interbreeding is no longer possible. What kind of speciation has occurred in this example, and what has driven it?
A. allopatric speciation, ecological isolation.
B. sympatric speciation, habitat differentiation. C. allopatric speciation, behavioural isolation. D. sympatric speciation, sexual selection.
E. sympatric speciation, allopolyploidy.
B.
87
Which of the following would be a position held by an adherent of the punctuated equilibrium theory?
A. A new species forms most of its unique features as it comes into existence and then changes little for the duration of its existence.
B. One should expect to find many transitional fossils left by organisms in the process of forming new species.
C. Given enough time, most existing species will gradually evolve into new species.
D. Natural selection is unimportant as a mechanism of evolution.
E. None of these.
A.
88
Speciation
A. occurs at such a slow pace that no one has ever observed the emergence of
new species.
B. occurs only by the accumulation of genetic change over vast expanses of time.
C. must begin with the geographic isolation of a small, frontier population.
D. proceeds at a uniform tempo across all taxa.
E. can involve changes involving a single gene.
E.
89
Which of the following statements about speciation is correct?
A. The goal of natural selection is speciation.
B. When reunited, two allopatric populations will not interbreed.
C. Natural selection chooses the reproductive barriers for populations.
D. Prezygotic reproductive barriers usually evolve before postzygotic barriers. E. Speciation is a basis for understanding macroevolution.
E.
90
What probably accounts for the switch to DNA-based genetic systems during the evolution of life on Earth?
A. DNA is chemically more stable and replicates with fewer errors (mutations) than RNA.
B. Only DNA can replicate during cell division.
C. RNA is too involved with translation of proteins and cannot provide multiple
functions.
D. DNA forms the rod-shaped chromosomes necessary for cell division.
E. Replication of RNA occurs too slowly.
A.
91
What is true of the fossil record of mammalian origins?
A. It is a good example of punctuated equilibrium.
B. It shows that mammals and birds evolved from the same kind of dinosaur. C. It includes transitional forms with progressively specialized teeth.
D. It indicates that mammals and dinosaurs did not overlap in geologic time. E. It includes a series that shows the gradual change of scales into fur.
C.
92
Which free-living cells were the earliest contributors to the formation of Earth’s oxidizing atmosphere?
A. cyanobacteria.
B. chloroplasts.
C. mitochondria.
D. seaweeds.
E. endosymbionts.
A.
93
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.
A. 4,3,2,1,5.
B. 4,1,2,3,5.
C. 4,1,3,2,5.
D. 4,3,1,5,2.
E. 3,4,1,2,5.
C.
94
A major evolutionary episode that corresponds in time most closely with the formation of Pangaea was the
A. origin of humans.
B. Cambrian explosion.
C. Permian extinctions.
D. Pleistocene ice ages.
E. Cretaceous extinctions.
C.
95
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
A. natural selection cannot account for the rise of the prokaryotic flagellum.
B. ancestral versions of this protein assemblage were either less functional, or
had different functions, than modern prokaryotic flagella.
C. scientists should accept the conclusion that neither eyes nor flagella could
have arisen by evolution.
D. we can conclude that both of these structures must have arisen through the
direct action of an ʺintelligent designerʺ. E. Both A and C are true.
B.
96
It has been found that certain proteins of the complex motor that drives bacterial flagella are modified versions of proteins that had previously belonged to plasma membrane pumps. This is evidence in support of the claim that
A. some structures are so complex that natural selection cannot, and will not, explain their origins.
B. the power of natural selection allows it to act in an almost predictive fashion, producing organs that will be needed in future environments.
C. the motors of bacterial flagella were originally synthesized abiotically.
D. natural selection can produce new structures by cobbling together parts of
other structures.
E. bacteria that possess flagella must have lost the ability to pump certain
chemicals across their plasma membranes.
D.
97
An 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, insect wings could best be described as
A. adaptations.
B. mutations.
C. exaptations.
D. isolating mechanisms.
E. examples of natural selection’s predictive ability.
C.
98
The existence of evolutionary trends, such as increasing body sizes among horse species, is evidence that
A. a larger volume-to-surface area ratio is beneficial to all mammals.
B. an unseen guiding force is at work.
C. evolution always tends toward increased complexity or increased size.
D. in particular environments, similar adaptations can be beneficial in more than
one species.
E. evolution generally progresses toward some predetermined goal.
D.
99
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
A. dinosaurs were as fully endothermal (warm-blooded) as modern birds and mammals.
B. their feathers originally served as insulation, and only later became flight surfaces.
C. the earliest reptiles could fly, and the feathers of flightless dinosaurs were vestigial flight surfaces.
D. the feathers were plucked from the bodies of other adults to provide nest- building materials.
E. all fossils with feathers are actually some kind of bird.
B.
100
The legless condition that is observed in several groups of extant reptiles is the result
of
A. their common ancestor having been legless.
B. a shared adaptation to an arboreal (living in trees) lifestyle.
C. several instances of the legless condition arising independently of each other.
D. individual lizards adapting to a fossorial (living in burrows) lifestyle during
their lifetimes.
E. none of these.
C.
101
The various taxonomic levels (viz, genera, classes, etc.) of the hierarchical classification system differ from each other on the basis of
A. how widely the organisms assigned to each are distributed throughout the environment.
B. the body sizes of the organisms assigned to each.
C. their inclusiveness.
D. the relative genome sizes of the organisms assigned to each.
E. morphological characters that are applicable to all organisms.
C.
102
Which of the following pairs are the best examples of homologous structures? A. bat wing and human hand.
B. owl wing and hornet wing.
C. porcupine quill and cactus spine.
D. bat forelimb and bird wing.
E. Australian mole and North American mole.
A.
103
If organisms A, B, and C belong to the same class but to different orders and if organisms D, E, and F belong to the same order but to different families, which of the following pairs of organisms would be expected to show the greatest degree of structural homology?
A. A and B. B. AandC. C. BandD. D. CandF. E. DandF.
E.
104
In angiosperm plants, flower morphology can be very intricate. If a tree, such as a New Mexico locust, has flowers that share many morphological intricacies with flowers of the sweet pea vine, then the most likely explanation for these floral similarities is the same general explanation for the similarities between the
A. dorsal fins of sharks and of dolphins.
B. reduced eyes of Australian moles and North American moles. C. scales on moth wings and the scales of fish skin.
D. cranial bones of humans and those of chimpanzees.
E. adaptations for flight in birds and adaptations for flight in bats.
D.
105
The common ancestors of birds and mammals were very early (stem) reptiles, which almost certainly possessed 3-chambered hearts (2 atria, 1 ventricle). Birds and mammals, however, are alike in having 4-chambered hearts (2 atria, 2 ventricles). The 4-chambered hearts of birds and mammals are best described as
A. structural homologies.
B. vestiges.
C. homoplasies.
D. the result of shared ancestry. E. molecular homologies.
C.
106
The term that is most appropriately associated with clade is A. paraphyletic.
B. polyphyletic.
C. monophyletic.
D. paralytic. E. monolytic.
C.
107
If birds are excluded from the class Reptilia, the term that consequently describes the class Reptilia is
A. paraphyletic. B. polyphyletic. C. monophyletic. D. paralytic.
E. monolytic.
A.
108
Use the Figure below to answer the following questions.
In the Figure above: A common ancestor for both species C and E could be at position number
A. 1.
B. 2.
C. 3.
D. 4.
E. 5.
D.
109
In the Figure above: The two extant (non-extinct) species that are most closely related to each other are
A. A and B. B. BandC. C. CandD. D. DandE. E. EandA.
C.
110
In the Figure above: Which species are extinct? A. A and E.
B. AandB.
C. CandD.
D. DandE.
E. cannot be determined from the information provided.
A.
111
If the eukaryotic condition arose, independently, several different times during evolutionary history, and if ancestors of these different lineages are extant and are classified in the domain Eukarya, then the domain Eukarya would be
A. paraphyletic.
B. polyphyletic.
C. monophyletic.
D. paralytic.
E. monolytic.
B.
112
Phylogenetic hypotheses (such as those represented by phylogenetic trees) are strongest when
A. they are based on amino acid sequences from homologous proteins, as long as the genes that code for such proteins contain no introns.
B. each clade is defined by a single derived character.
C. they are supported by more than one kind of evidence, such as when fossil
evidence corroborates molecular evidence.
D. they are accepted by the foremost authorities in the field, especially if they
have won Nobel Prizes.
E. they are based on a single DNA sequence that seems to be a shared derived
sequence.
C.
113
A researcher compared the nucleotide sequences of a homologous gene from five different species of mammals with the homologous human gene. The sequence homology between each speciesʹ version of the gene and the human gene is presented as a percentage of similarity.
Species Percentage (%)
Chimpanzee 99.7
Orangutan 98.6
Baboon 97.2
Rhesus Monkey 96.9
Rabbit 93.7
What probably explains the inclusion of rabbits in this research?
A. Their short generation time provides a ready source of DNA.
B. They possess all of the shared derived characters as do the other species
listed.
C. They are the closest known relatives of rhesus monkeys.
D. They are the outgroup.
E. They are the most recent common ancestor of the primates.
D.
114
A researcher compared the nucleotide sequences of a homologous gene from five different species of mammals with the homologous human gene. The sequence homology between each speciesʹ version of the gene and the human gene is presented as a percentage of similarity.
Species Percentage (%)
Chimpanzee 99.7
Orangutan 98.6
Baboon 97.2
Rhesus Monkey 96.9
Rabbit 93.7
Concerning growth in genome size over evolutionary time, which of these does not belong with the others?
A. orthologous genes.
B. gene duplications.
C. paralogous genes.
D. gene families.
E. None of these belong with the others.
A.
115
A researcher compared the nucleotide sequences of a homologous gene from five different species of mammals with the homologous human gene. The sequence homology between each speciesʹ version of the gene and the human gene is presented as a percentage of similarity.
Species Percentage (%)
Chimpanzee 99.7
Orangutan 98.6
Baboon 97.2
Rhesus Monkey 96.9
Rabbit 93.7
Species that are not closely related and that do not share many anatomical similarities can still be placed together on the same phylogenetic tree by comparing their
A. plasmids.
B. chloroplast genomes.
C. mitochondrial genomes.
D. homologous genes that are poorly conserved.E. homologous genes that are highly conserved
E.
116
A researcher compared the nucleotide sequences of a homologous gene from five different species of mammals with the homologous human gene. The sequence homology between each speciesʹ version of the gene and the human gene is presented as a percentage of similarity.
Species Percentage (%)
Chimpanzee 99.7
Orangutan 98.6
Baboon 97.2
Rhesus Monkey 96.9
Rabbit 93.7
The reason that paralogous genes can diverge from each other within the same gene pool, whereas orthologous genes diverge only after gene pools are isolated from each other, is that
A. having multiple copies of genes is essential for the occurrence of sympatric speciation in the wild.
B. paralogous genes can occur only in diploid species; thus, they are absent from most prokaryotes.
C. polyploidy is a necessary precondition for the occurrence of sympatric speciation in the wild.
D. having an extra copy of a gene permits modifications to the copy without loss of the original gene product.
E. none of these.
D.
117
A researcher compared the nucleotide sequences of a homologous gene from five different species of mammals with the homologous human gene. The sequence homology between each speciesʹ version of the gene and the human gene is presented as a percentage of similarity.
Species Percentage (%)
Chimpanzee 99.7
Orangutan 98.6
Baboon 97.2
Rhesus Monkey 96.9
Rabbit 93.7
The human nuclear genome includes hundreds of genes that are orthologs of bacterial genes, and hundreds of other genes that are orthologs of archaean genes. This finding can be explained by proposing that
A. neither archaea nor bacteria contain paralogous genes.
B. the eukaryotic lineage leading to humans involved at least one fusion of an
ancient bacterium with an ancient archaean.
C. the infection of humans by bacteriophage introduced prokaryotic genes into
the human genome.
D. horizontal gene transfer did not occur to any significant extent among the
prokaryotic ancestors of humans.
B.
118
A researcher compared the nucleotide sequences of a homologous gene from five different species of mammals with the homologous human gene. The sequence homology between each speciesʹ version of the gene and the human gene is presented as a percentage of similarity.
Species Percentage (%)
Chimpanzee 99.7
Orangutan 98.6
Baboon 97.2
Rhesus Monkey 96.9
Rabbit 93.7
A large proportion of archaeans are ʺextremophilesʺ, so called because they inhabit extreme environments with high acidity and/or high temperature. Such environments are thought to have been much more common on the primitive Earth. Thus, modern extremophiles survive only in places that their ancestors became adapted to long ago. Which of these is, consequently, a valid statement about modern extremophiles, assuming that their habitats have remained relatively unchanged?
A. Among themselves, they should share relatively few ancestral traits, especially those that enabled ancestral forms to adapt to extreme conditions.
B. On a phylogenetic tree whose branch lengths are proportional to amount of genetic change, the branches of the extremophiles should be shorter, relative
to branches of the non-extremophilic archaeans.
C. They should contain genes that originated in eukaryotes that are the hosts for
numerous species of bacteria.
D. They should currently be undergoing a high level of horizontal gene transfer
with non-extremophilic archaeans.
B.
