A30fiffAnswers
- b
- Shallow water, oxygen-poor water, areas with seasonal
flooding, and nutrient-poor water but nutrient-rich land.- Possible answers include (a) shark; (b) hagfish; (c) bird;
(d) f r o g.- It suggests that Neanderthals evolved and left Africa before
modern humans evolved in Africa, and that modern humans
intermingled with Neanderthal populations only after leaving
Africa.ANSWERS TO FIGURE QUESTIONS
Figure 17.2
Q1: Are mollusks more closely related to flatworms or to annelids?
Explain your reasoning.
A1: Mollusks share a more recent common ancestor with
annelids than with flatworms, so they are more closely related to
annelids.
Q2: If you found an animal with no symmetry, to what group
would it belong? Give an example of an animal that is radially
symmetrical, and one that is bilaterally symmetrical.
A2: Animals with no symmetry are sponges. Animals with radial
symmetry include cnidarians and echinoderms (secondarily).
Animals with bilateral symmetry include flatworms, mollusks,
annelids, nematodes, arthropods, and chordates.
Q3: How do we know that a sponge is an animal, and not a plant or
an alga?
A3: Sponges are heterotrophic, not autotrophic like plants and
algae.
Figure 17.3
Q1: Do amphibians have amniotic eggs?
A1: No.
Q2: What group of animals has jaws but not a bony skeleton?
A2: Sharks and rays.
Q3: When people talk about animals, they are sometimes referring
only to mammals. How would you explain to them their error?
A3: Mammals are a subset of a much larger group; animals
include invertebrates, birds, and lizards, among other things.
Figure 17.4
Q1: Is a sea star radially or bilaterally symmetrical?
A1: Radially symmetrical.
Q2: What advantage might a bilaterally symmetrical animal have
over one that is radially symmetrical, and vice versa?
A2: Animals with bilateral symmetry move more efficiently.
Those with radial symmetry have 360-degree access to their
environment.
Q3: What kind of symmetry do you (a human) have?A3: Bilateral.Figure 17.5
Q1: List all of the lobster’s thoracic appendages.A1: Walking legs, crushing claw, cutting claw.Q2: Which of the lobster’s appendages is most important for
sensing the environment?A2: The head appendage, which includes eyes and antennae.Q3: What body segments do you (a human) have?A3: Head, thorax, and abdomen.Figure 17.6
Q1: The Virginia opossum, or possum, is the only North American
marsupial. Describe how its young are born and develop.A1: They are born relatively undeveloped and crawl into the
mother’s pouch, where they nurse and grow.Q2: If you were a monotreme, would you still produce milk and
nurse your young?A2: Yes; all mammals do.Q3: What kind of mammal is a cow? How about a human?A3: Cows and humans are eutherians.Figure 17.7
Q1: According to this evolutionary tree, which primate group is
most closely related to humans?A1: Chimpanzees.Q2: According to this evolutionary tree, which primate group is
most distantly related to humans?A2: Lemurs, along with others in this branch.Q3: What characteristics are common to all the primates,
including humans? (You will need to read the next paragraph to
answer this question.)A3: The use of tools, a capacity for symbolic language, and the
performance of deliberate acts of deception.Figure 17.8
Q1: Through natural selection, deleterious traits will tend to
disappear from a population over time. Which traits might have
been deleterious for ground-dwelling early hominins?A1: Opposable toes; walking on four limbs.Q2: Through natural selection, advantageous traits will tend to
persist in a population over time. Which traits might have been
advantageous for ground-dwelling early hominins?A2: Upright posture; arched feet.Q3: Adaptations to upright walking also mean that human females
have more difficulty giving birth than do females of other species.
What adaptation would you predict has had the greatest impact on
this result?A3: Reorganization of the pelvic structure.