How Humans Evolved 10th Edition Test Bank - Boyd
1. A researcher discovers a fossil primate with a postorbital bar but not a postorbital septum, an
unfused mandibular symphysis, and a toothcomb. Based on these traits, to which extant primate
group is this fossil most likely related?
A. Strepsirrhini
B. Haplorhini
C. Catarrhini
D. Platyrrhini
Answer: A
Rationale: The postorbital bar (but no septum), unfused mandibular symphysis, and toothcomb are
derived traits of strepsirrhines (lemurs and lorises). Haplorhines have a postorbital septum; catarrhines
and platyrrhines are haplorhines with fused mandibular symphyses and lack toothcombs.
2. In a phylogenetic analysis of hominins, a researcher finds that the genus Australopithecus is
paraphyletic. Which of the following best explains this result?
A. Australopithecus species are more closely related to each other than to any other hominin
B. Some Australopithecus species share a more recent common ancestor with Homo than with other
Australopithecus species
C. All australopiths are direct ancestors of modern humans
D. Australopithecus afarensis is the last common ancestor of all later hominins
Answer: B
Rationale: Paraphyly of Australopithecus means that some of its species (e.g., A. garhi) are more closely
related to Homo than to other australopiths, excluding them from a monophyletic group. This reflects
the mosaic evolution of Homo-like traits.
3. A study comparing the 13C values of enamel from Paranthropus boisei and early Homo from
the same stratigraphic layer shows that P. boisei has consistently higher 13C values. What dietary
inference is most supported?
A. Both species consumed similar proportions of C3 and C4 plants
B. P. boisei relied more heavily on C4 plants (e.g., grasses, sedges) than early Homo
C. Early Homo consumed more meat than P. boisei
D. P. boisei lived in a more forested environment than early Homo
Answer: B
Rationale: Higher ´13C values indicate greater consumption of C4 plants (tropical grasses, sedges)
compared to C3 plants (trees, shrubs, most fruits). This suggests P. boisei was a specialized C4 feeder,
while early Homo had a more varied diet including C3 resources.
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,4. Which of the following observations best supports the hypothesis that the last common ancestor
of chimpanzees and humans had a knuckle-walking adaptation?
A. Human wrist bones share derived features with knuckle-walking apes
B. Chimpanzees and gorillas both knuckle-walk, indicating convergent evolution
C. Fossil hominins show evidence of knuckle-walking
D. Molecular data show that the human-chimp split occurred after the evolution of knuckle-walking
Answer: A
Rationale: Human wrists (e.g., the scaphoid and lunate) share specific morphological features with
knuckle-walking apes that are absent in other primates, suggesting a common knuckle-walking ancestor.
Option B describes convergent evolution, which could also explain the trait, but shared derived features
are stronger evidence for homology.
5. A paleoanthropologist finds a hominin cranium with a cranial capacity of 750 cc, a pronounced
occipital torus, a receding forehead, and a projecting face. Which species assignment is most
consistent with these traits?
A. Homo erectus
B. Homo habilis
C. Homo neanderthalensis
D. Australopithecus africanus
Answer: A
Rationale: Cranial capacity ~750 cc, occipital torus, receding forehead, and facial prognathism are
characteristic of early Homo erectus (e.g., from Dmanisi). Homo habilis has smaller cranial capacity
(~500-600 cc) and less pronounced torus; Neanderthals have larger brains and different features;
Australopithecus africanus has even smaller brains (~450 cc).
6. In a population of modern humans, the frequency of the derived allele at the EDAR gene
(V370A) is 0.8 in East Asia but nearly absent in Africa. Which evolutionary scenario best explains
this pattern?
A. The derived allele arose recently in Africa and then swept to fixation in East Asia due to selection
B. The derived allele was present in the ancestral population but lost in Africa due to genetic drift
C. The derived allele introgressed from archaic hominins into East Asian populations
D. The derived allele is under balancing selection in Africa
Answer: B
Rationale: The EDAR V370A allele is derived and found at high frequency in East Asia but is nearly
absent in Africa. This pattern is best explained by a recent selective sweep in East Asia after the
out-of-Africa migration, with the allele being rare or absent in the ancestral African population due to
drift or loss.
7. A researcher sequences the genome of a Neanderthal fossil and finds that the individual carries a
haplotype associated with reduced risk of severe COVID-19. However, this haplotype is absent in
all sequenced Neanderthals from Europe. What is the most likely explanation?
A. The haplotype arose in Neanderthals after the European lineage split off
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,B. The haplotype was introduced into Neanderthals via gene flow from early modern humans
C. The haplotype is an artifact of contamination with modern human DNA
D. The haplotype was lost in European Neanderthals due to a population bottleneck
Answer: A
Rationale: The haplotype's presence in a Neanderthal but absence in European Neanderthals suggests it
evolved in a different Neanderthal population (e.g., Siberian) after divergence from European
Neanderthals. Gene flow from modern humans is less likely because the haplotype is now common in
modern humans and could have been inherited from Neanderthals, but the absence in European
Neanderthals argues against it being widespread.
8. Which of the following best explains why the human pelvis is relatively broad and mediolaterally
oriented compared to that of chimpanzees?
A. Adaptation for a larger birth canal due to encephalization
B. Adaptation for more efficient quadrupedal walking
C. Adaptation for climbing and suspensory behavior
D. Adaptation for a more stable center of mass during bipedalism
Answer: D
Rationale: The broad, mediolaterally oriented human pelvis positions the hip joints laterally, which helps
balance the trunk during bipedal walking by reducing the moment arm of the upper body. While
encephalization also influences pelvic shape (birth canal), the primary selective pressure for the broad
ilia is bipedal locomotion.
9. A researcher finds that in a population of baboons, females who form strong social bonds with
other females have higher offspring survival rates. Which evolutionary mechanism is most directly
supported?
A. Kin selection
B. Reciprocal altruism
C. Direct fitness benefits through cooperation
D. Sexual selection
Answer: C
Rationale: Increased offspring survival due to social bonds directly enhances the female's own
reproductive success (direct fitness). While kin selection could be involved if bonds are with relatives,
the question does not specify relatedness. Reciprocal altruism implies future repayment, which is not
necessary here; direct benefits from cooperation (e.g., protection, alloparenting) are sufficient.
10. Which of the following is a key prediction of the expensive tissue hypothesis regarding human
brain evolution?
A. Brain expansion was accompanied by a reduction in gut size
B. Brain expansion was enabled by a shift to a high-quality diet
C. Brain expansion led to a decrease in overall metabolic rate
D. Brain expansion required a longer lifespan to recoup energy costs
Answer: A
Page 3
, Rationale: The expensive tissue hypothesis (Aiello & Wheeler) posits that the high metabolic cost of a large brain in humans
was offset by a reduction in the size of other metabolically expensive tissues, particularly the gastrointestinal tract. Option B
(high-quality diet) is a complementary hypothesis but not the core of the expensive tissue hypothesis.
11. A fossil hominin mandible from the site of Dmanisi (Georgia, dated to ~1.8 Ma) exhibits a small
brain size (~600 cc), a primitive dentition, and a body size similar to modern humans. Which of the
following interpretations is most consistent with current paleoanthropological consensus regarding
the taxonomic status of early Homo?
A. The Dmanisi specimens represent a single variable species, Homo erectus, and demonstrate that early Homo
was more morphologically diverse than previously thought.
B. The Dmanisi fossils are best classified as Homo habilis, indicating that Homo habilis survived until 1.8 Ma
in Eurasia.
C. The Dmanisi specimens represent a separate species, Homo georgicus, due to their unique combination of
primitive and derived traits.
D. The Dmanisi fossils are evidence of a migration event from Africa by Homo rudolfensis, which then evolved
into Homo erectus in Eurasia.
Answer: A
Rationale: The Dmanisi fossils show a range of morphological variation that falls within the variation
seen in later Homo erectus, and the current consensus is that they represent an early population of H.
erectus with high variability. Option B is unlikely because H. habilis is generally restricted to Africa.
Option C is a minority view not widely accepted. Option D is not supported as H. rudolfensis is not
considered ancestral to H. erectus in Eurasia.
12. In a study of genomic variation among modern human populations, researchers find that
Neanderthal-derived alleles are more common in East Asian populations than in European
populations. Which of the following evolutionary processes best explains this pattern?
A. Natural selection favored Neanderthal alleles more strongly in East Asian environments than in European
environments.
B. Gene flow from Neanderthals into the ancestors of East Asians occurred after the split from Europeans,
leading to a higher proportion of Neanderthal ancestry.
C. The ancestors of Europeans experienced a population bottleneck that reduced Neanderthal ancestry, while
East Asian populations did not.
D. Neanderthal alleles were introduced into East Asian populations via secondary gene flow from Denisovans,
who had previously admixed with Neanderthals.
Answer: B
Rationale: The most parsimonious explanation is that the ancestors of East Asians received additional
gene flow from Neanderthals after the divergence of European and East Asian lineages, possibly during
a separate migration wave. Option A is less supported because there is no evidence of differential
selection. Option C is unlikely because both populations experienced bottlenecks. Option D is
speculative and not necessary to explain the pattern.
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1. A researcher discovers a fossil primate with a postorbital bar but not a postorbital septum, an
unfused mandibular symphysis, and a toothcomb. Based on these traits, to which extant primate
group is this fossil most likely related?
A. Strepsirrhini
B. Haplorhini
C. Catarrhini
D. Platyrrhini
Answer: A
Rationale: The postorbital bar (but no septum), unfused mandibular symphysis, and toothcomb are
derived traits of strepsirrhines (lemurs and lorises). Haplorhines have a postorbital septum; catarrhines
and platyrrhines are haplorhines with fused mandibular symphyses and lack toothcombs.
2. In a phylogenetic analysis of hominins, a researcher finds that the genus Australopithecus is
paraphyletic. Which of the following best explains this result?
A. Australopithecus species are more closely related to each other than to any other hominin
B. Some Australopithecus species share a more recent common ancestor with Homo than with other
Australopithecus species
C. All australopiths are direct ancestors of modern humans
D. Australopithecus afarensis is the last common ancestor of all later hominins
Answer: B
Rationale: Paraphyly of Australopithecus means that some of its species (e.g., A. garhi) are more closely
related to Homo than to other australopiths, excluding them from a monophyletic group. This reflects
the mosaic evolution of Homo-like traits.
3. A study comparing the 13C values of enamel from Paranthropus boisei and early Homo from
the same stratigraphic layer shows that P. boisei has consistently higher 13C values. What dietary
inference is most supported?
A. Both species consumed similar proportions of C3 and C4 plants
B. P. boisei relied more heavily on C4 plants (e.g., grasses, sedges) than early Homo
C. Early Homo consumed more meat than P. boisei
D. P. boisei lived in a more forested environment than early Homo
Answer: B
Rationale: Higher ´13C values indicate greater consumption of C4 plants (tropical grasses, sedges)
compared to C3 plants (trees, shrubs, most fruits). This suggests P. boisei was a specialized C4 feeder,
while early Homo had a more varied diet including C3 resources.
Page 1
,4. Which of the following observations best supports the hypothesis that the last common ancestor
of chimpanzees and humans had a knuckle-walking adaptation?
A. Human wrist bones share derived features with knuckle-walking apes
B. Chimpanzees and gorillas both knuckle-walk, indicating convergent evolution
C. Fossil hominins show evidence of knuckle-walking
D. Molecular data show that the human-chimp split occurred after the evolution of knuckle-walking
Answer: A
Rationale: Human wrists (e.g., the scaphoid and lunate) share specific morphological features with
knuckle-walking apes that are absent in other primates, suggesting a common knuckle-walking ancestor.
Option B describes convergent evolution, which could also explain the trait, but shared derived features
are stronger evidence for homology.
5. A paleoanthropologist finds a hominin cranium with a cranial capacity of 750 cc, a pronounced
occipital torus, a receding forehead, and a projecting face. Which species assignment is most
consistent with these traits?
A. Homo erectus
B. Homo habilis
C. Homo neanderthalensis
D. Australopithecus africanus
Answer: A
Rationale: Cranial capacity ~750 cc, occipital torus, receding forehead, and facial prognathism are
characteristic of early Homo erectus (e.g., from Dmanisi). Homo habilis has smaller cranial capacity
(~500-600 cc) and less pronounced torus; Neanderthals have larger brains and different features;
Australopithecus africanus has even smaller brains (~450 cc).
6. In a population of modern humans, the frequency of the derived allele at the EDAR gene
(V370A) is 0.8 in East Asia but nearly absent in Africa. Which evolutionary scenario best explains
this pattern?
A. The derived allele arose recently in Africa and then swept to fixation in East Asia due to selection
B. The derived allele was present in the ancestral population but lost in Africa due to genetic drift
C. The derived allele introgressed from archaic hominins into East Asian populations
D. The derived allele is under balancing selection in Africa
Answer: B
Rationale: The EDAR V370A allele is derived and found at high frequency in East Asia but is nearly
absent in Africa. This pattern is best explained by a recent selective sweep in East Asia after the
out-of-Africa migration, with the allele being rare or absent in the ancestral African population due to
drift or loss.
7. A researcher sequences the genome of a Neanderthal fossil and finds that the individual carries a
haplotype associated with reduced risk of severe COVID-19. However, this haplotype is absent in
all sequenced Neanderthals from Europe. What is the most likely explanation?
A. The haplotype arose in Neanderthals after the European lineage split off
Page 2
,B. The haplotype was introduced into Neanderthals via gene flow from early modern humans
C. The haplotype is an artifact of contamination with modern human DNA
D. The haplotype was lost in European Neanderthals due to a population bottleneck
Answer: A
Rationale: The haplotype's presence in a Neanderthal but absence in European Neanderthals suggests it
evolved in a different Neanderthal population (e.g., Siberian) after divergence from European
Neanderthals. Gene flow from modern humans is less likely because the haplotype is now common in
modern humans and could have been inherited from Neanderthals, but the absence in European
Neanderthals argues against it being widespread.
8. Which of the following best explains why the human pelvis is relatively broad and mediolaterally
oriented compared to that of chimpanzees?
A. Adaptation for a larger birth canal due to encephalization
B. Adaptation for more efficient quadrupedal walking
C. Adaptation for climbing and suspensory behavior
D. Adaptation for a more stable center of mass during bipedalism
Answer: D
Rationale: The broad, mediolaterally oriented human pelvis positions the hip joints laterally, which helps
balance the trunk during bipedal walking by reducing the moment arm of the upper body. While
encephalization also influences pelvic shape (birth canal), the primary selective pressure for the broad
ilia is bipedal locomotion.
9. A researcher finds that in a population of baboons, females who form strong social bonds with
other females have higher offspring survival rates. Which evolutionary mechanism is most directly
supported?
A. Kin selection
B. Reciprocal altruism
C. Direct fitness benefits through cooperation
D. Sexual selection
Answer: C
Rationale: Increased offspring survival due to social bonds directly enhances the female's own
reproductive success (direct fitness). While kin selection could be involved if bonds are with relatives,
the question does not specify relatedness. Reciprocal altruism implies future repayment, which is not
necessary here; direct benefits from cooperation (e.g., protection, alloparenting) are sufficient.
10. Which of the following is a key prediction of the expensive tissue hypothesis regarding human
brain evolution?
A. Brain expansion was accompanied by a reduction in gut size
B. Brain expansion was enabled by a shift to a high-quality diet
C. Brain expansion led to a decrease in overall metabolic rate
D. Brain expansion required a longer lifespan to recoup energy costs
Answer: A
Page 3
, Rationale: The expensive tissue hypothesis (Aiello & Wheeler) posits that the high metabolic cost of a large brain in humans
was offset by a reduction in the size of other metabolically expensive tissues, particularly the gastrointestinal tract. Option B
(high-quality diet) is a complementary hypothesis but not the core of the expensive tissue hypothesis.
11. A fossil hominin mandible from the site of Dmanisi (Georgia, dated to ~1.8 Ma) exhibits a small
brain size (~600 cc), a primitive dentition, and a body size similar to modern humans. Which of the
following interpretations is most consistent with current paleoanthropological consensus regarding
the taxonomic status of early Homo?
A. The Dmanisi specimens represent a single variable species, Homo erectus, and demonstrate that early Homo
was more morphologically diverse than previously thought.
B. The Dmanisi fossils are best classified as Homo habilis, indicating that Homo habilis survived until 1.8 Ma
in Eurasia.
C. The Dmanisi specimens represent a separate species, Homo georgicus, due to their unique combination of
primitive and derived traits.
D. The Dmanisi fossils are evidence of a migration event from Africa by Homo rudolfensis, which then evolved
into Homo erectus in Eurasia.
Answer: A
Rationale: The Dmanisi fossils show a range of morphological variation that falls within the variation
seen in later Homo erectus, and the current consensus is that they represent an early population of H.
erectus with high variability. Option B is unlikely because H. habilis is generally restricted to Africa.
Option C is a minority view not widely accepted. Option D is not supported as H. rudolfensis is not
considered ancestral to H. erectus in Eurasia.
12. In a study of genomic variation among modern human populations, researchers find that
Neanderthal-derived alleles are more common in East Asian populations than in European
populations. Which of the following evolutionary processes best explains this pattern?
A. Natural selection favored Neanderthal alleles more strongly in East Asian environments than in European
environments.
B. Gene flow from Neanderthals into the ancestors of East Asians occurred after the split from Europeans,
leading to a higher proportion of Neanderthal ancestry.
C. The ancestors of Europeans experienced a population bottleneck that reduced Neanderthal ancestry, while
East Asian populations did not.
D. Neanderthal alleles were introduced into East Asian populations via secondary gene flow from Denisovans,
who had previously admixed with Neanderthals.
Answer: B
Rationale: The most parsimonious explanation is that the ancestors of East Asians received additional
gene flow from Neanderthals after the divergence of European and East Asian lineages, possibly during
a separate migration wave. Option A is less supported because there is no evidence of differential
selection. Option C is unlikely because both populations experienced bottlenecks. Option D is
speculative and not necessary to explain the pattern.
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