Biology Now, 2e

Answers ■ A31

Figure 17.9

Q1: What other reason besides continuing to use trees might

explain why early hominins had partially opposable big toes?

A1: This trait may have taken a long, long time to lose. A major

change in structure cannot occur within a few generations. It was

likely a gradual change over thousands of generations.

Q2: In what way does the pattern of footprints in this figure

suggest that the print makers were walking upright?

A2: No hand or knuckle prints accompany the footprints.

Q3: Why do you think we no longer have partially opposable big

toes?

A3: The opposable big toes would have made walking upright or

running more difficult. If we no longer returned to the trees, there

was no selective advantage to having them. In fact, individuals

with fully opposable toes were at a disadvantage.

Figure 17.10

Q1: Where would the Neanderthal species branch be on this tree?

A1: The Homo neanderthalensis lineage would branch either from

the common ancestor of H. erectus and H. sapiens, or from H.

erectus along with H. sapiens. The exact hereditary line for these

two closely related species is still unclear.

Q2: How would the Neanderthal skull differ from the Homo

erectus skull?

A2: The skull would be larger, more like the H. sapiens skull size

or larger.

Q3: How would the Neanderthal skull differ from the Homo

sapiens skull?

A3: The skull would be longer, the forehead would slope more, and

there would be no chin.

Figure 17.11

Q1: Why does mitochondrial DNA come only from your mother?

A1: Mitochondria are found in the egg but not the sperm. Eggs are

from your mom, and sperm are from your dad.

Q2: If a Neanderthal-human hybrid was born to a human mother

and a Neanderthal father, could you tell by mitochondrial-DNA

sequencing?

A2: No. All the mitochondrial DNA would be from Homo sapiens.

Q3: If a Neanderthal-human hybrid was born to a human father

and a Neanderthal mother, could you tell by mitochondrial-DNA

sequencing?

A3: Yes. In this case, all the mitochondrial DNA would be from

Homo neanderthalensis.

Figure 17.12

Q1: If a human-Neanderthal hybrid was born to a human mother

and a Neanderthal father, could you tell by whole-genome DNA

sequencing that it was a hybrid?

A1: Yes. The offspring would have nuclear DNA from both the egg

and the sperm.

Q2: If a human-Neanderthal hybrid was born to a Neanderthal

mother and a human father, could you tell by whole-genome DNA

sequencing that it was a hybrid?

A2: Yes. The offspring would have nuclear DNA from both the egg

and the sperm.

Q3: Under what circumstances are scientists able to do

whole-genome sequencing, and when are they restricted to

mitochondrial-DNA sequencing?

A3: Whole-genome sequencing requires well-preserved cells or

tissues with fully intact DNA. Mitochondrial DNA can be isolated

from cells and tissues that aren’t so well preserved and from

damaged DNA.

Figure 17.13

Q1: Are you surprised by the interpretations of the hominins in

this picture?’ Why or why not?

A1: This question asks for an opinion. One possible answer: Homo

sapiens looks more primitive than expected, and the other species

look strikingly like us.

Q2: Describe the main differences that distinguish the hominin

species.

A2: Height, musculature, size of skull, slope of forehead, amount

of hair and its location.

Q3: From what you’ve learned about these species, do you think

these representations are accurate? How can you find more

information about each species to help you answer this question?

A3: The first part of the question asks for an opinion. One possible

answer for the second part: I can do much more extensive research

about all of our family members online and at museums of natural

histor y.

Figure 17.14

Q1: What evidence suggests that Neanderthals never lived in

Africa?

A1: Modern humans of African descent have neither

mitochondrial nor nuclear Neanderthal DNA sequences in their

genomes.

Q2: How does the hypothesized origin of modern humans (Homo

sapiens) differ from the hypothesized origin of Neanderthals

(Homo neanderthalensis)?

A2: Modern humans evolved from archaic humans in Africa and

spread to the rest of the world. Neanderthals are thought to have

evolved from archaic humans living in the Middle East.

Q3: What species of hominins other than the Neanderthals may

have commingled with modern humans?

A3: Homo erectus.

Figure 17.15

Q1: Describe the difference you observe between the modern

human skull’s chin and the Neanderthal skull’s lower jaw.

A1: The human chin is higher and juts out further.

Q2: What other differences do you observe between the two skulls?