Answers and Explanations—6.8 Signaling Theory

P1	Paragraph 1	Comments
S1	There is a history of controversy within evolutionary biology over why honesty exists in animal communication.	Why is animal communication honest?
2	All animals, humans included, engage in communication that involves both a sender and a receiver, and this communication occurs both within and across species.	All animals communicate.
3	The sender communicates a signal to a receiver, who then acts upon that signal.	Communication = send + receive signals.
4	Male peacocks seek to signal their worthiness to females of the species by growing vibrant tail feathers, and gazelles engage in spectacular leaping displays, called stotting, upon seeing approaching predators in order to indicate their athletic prowess and therefore dissuade the predator from attacking.	Examples.

	According to paragraph 1, what is true of animal communication?	Fact. All of P1 discusses animal communication. The correct answer must be supported in the text.
✗	A It often indicates the athletic prowess of the sender.	S4 mentions that gazelles communicate their athletic prowess in a certain way. But this is not necessarily the case with all or even most animal communication.
✓	B It involves a receiver who acts upon the communication sent.	Correct. S3: “The sender communicates a signal to a receiver, who then acts upon that signal.”
✗	C Senders and receivers must be of the same species.	S2: “this communication occurs both within and across species.”
✗	D Evolutionary biologists agree on the reasons why it is honest.	S1: “There is a history of controversy within evolutionary biology over why honesty exists in animal communication.”

P2	Paragraph 2	Comments
S1	In some cases, a signal may be honest, meaning that the sender is conveying accurate information, but signals can also be dishonest when the sender is providing false information to a receiver.	Honest and dishonest signals.
2	All signals, however, share the additional feature of being costly to produce and send.	All signals are costly.
3	A peacock’s tail feathers have significant weight and take excessive energy to produce.	Examples.
4	A bird chirping to alert others in the flock of a nearby predator has now exposed its own location to that same predator, potentially making it more vulnerable to attack.

	Why does the author mention “a bird chirping to alert others”?	Purpose. The chirping (in S4) is an example of a signal that has a cost to the signaler. The general point is made in S2.
✗	A To point out an example of a dishonest signal	Both examples in this paragraph are honest signals.
✗	B To illustrate cross-species communication	This signal is not cross-species. It is prompted by a predator (almost certainly of a different species), but the bird is chirping to alert other birds in its flock, which are of the same species.
✗	C To outline the requirements of an honest signal	This example is of an honest signal. But it does not describe any particular requirements of an honest signal.
✓	D To show how some signals are costly to send	Correct. S2 makes the point that all signals are costly to the sender. The example of the bird chirping in S4 illustrates this point. This chirping helps other birds but can put the chirping bird in even more danger.

	The word “conveying” in the passage is closest in meaning to	VOCABULARY. “Convey” = transmit, communicate, send.
✓	A transmitting	Correct. “The sender is conveying accurate information” = the sender is transmitting or communicating accurate information.
✗	B interpreting	The sender is sending the messages, not “interpreting” (explaining) them.
✗	C withholding	Opposite. “Withholding” = retaining or refusing to give.
✗	D manufacturing	Not quite. “Manufacturing” signals would mean to create, devise, or even invent signals. The sender isn’t necessarily making up new signals. They are communicating signals that might already exist.

P3	Paragraph 3	Comments
S1	Biologists have found that, in general, animals communicate with honest signals, but why?	Why are animals honest?
2	Deception would seem to provide short-term gains.	Lying seems useful (in short run).
3	For example, the male fiddler crab is known for its one large fighting claw, which it uses to compete for a mate with other male crabs.	Example of dishonest fiddler crab.
4	If a fiddler crab loses its claw in the fight, another claw that is lighter in weight and therefore less effective grows in its place.
5	Although the crab can still scare off other mates with its new claw that is similar in size to the original, it is sending the dishonest signal to other males that it is strong and able to fight, although if challenged it would likely lose.
6	Scientists theorize that signals must be honest on average, at least to a certain degree.	Scientists: signals must generally be honest or they’ll stop working.
7	If not, the intended receiver would eventually evolve to ignore the signal, rendering it useless.
8	In the early 1970s, biologist Amotz Zahavi proposed the handicap principle: honesty is maintained through handicaps, or high-cost signals, which are naturally more believable.	Handicap = high-cost signal = more believable.

	According to paragraph 3, all of the following are characteristics of the replacement claw grown by a fiddler crab EXCEPT:	Negative Fact. S3–5 contain the fiddler crab example. S4–5 focus on the replacement claw. Three answer choices will be mentioned in the paragraph. One answer choice will not be.
✗	A It is similar in size to the original claw.	S5: “Its new claw… is similar in size to the original.”
✗	B It is not as heavy as the original claw.	S4: “another claw that is lighter in weight… grows in its place.”
✓	C It is no less effective than the original claw.	Correct. S4: “Another claw that is… less effective grows in its place.”
✗	D It functions as a dishonest signal.	S5: “it is sending the dishonest signal to other males.”

P4	Paragraph 4	Comments
S1	The handicap principle relies on the assumption that prominent signals of fighting ability or selection may be impossible, or impossibly costly, to fake.	Handicap principle: prominent signals can’t be faked.
2	For example, a full-grown bull elk’s rack of antlers may weigh in excess of 40 pounds, a weight greater than a young, weak, or sickly individual could hope to carry.	Example of elk antlers. Only strong can grow.
3	Therefore, an elk able to grow a large rack of antlers is honestly signaling its ability to defend itself in a fight.
4	Male peacock tail feathers present the same honest signal to females about the male’s strength and desirability as a mate.	Example of peacock tail. Only strong can deal with the handicap.
5	The long tail not only takes significant effort to produce, but also creates issues for survival.
6	The bright colors are more attractive to predators, and the length of the tail somewhat restricts flight and therefore the bird’s ability to escape pursuit.
7	As with the elk, a weaker or sicklier bird could not afford to produce such ornamentation.
8	In both examples, the signal of strength is, in actuality, a handicap to the animal sending it.	Both examples: the signal of strength is the costly handicap.

	According to paragraph 4, the antlers of a full-grown bull elk are useful because	Fact. S2–3 discuss the example of a bull elk’s antlers.
✓	A large, heavy antlers act as an authentic signal of strength	Correct. S3: “An elk able to grow a large rack of antlers is honestly signaling its ability to defend itself in a fight.”
✗	B they allow scientists to estimate the age of the bull elk	This point is not mentioned in the paragraph.
✗	C they can be faked by sickly elks, which can then avoid costly fights	S2 indicates that sickly elks cannot carry such heavy racks of antlers.
✗	D they restrict the elk’s ability to escape pursuit	This point is made in S6 about a peacock’s tail feathers, not about the elk’s antlers.

	The phrase “in actuality” in the passage is closest in meaning to	VOCABULARY. “Actuality” = reality, the real world.
✗	A in theory	Opposite. When talking about something “in theory,” the speaker is hypothesizing rather than saying it is definitely true.
✗	B intentionally	The signal would not be an “intentional” (deliberate or calculated) handicap.
✓	C in reality	Correct. “The signal of strength is, in actuality, a handicap” = the signal is, in reality, a handicap.
✗	D unfortunately	While the handicap is likely unfortunate for the animal, these words are not synonyms.

P5	Paragraph 5	Comments
S1	Thus, these revealing handicaps are honest signals of strength in the sense that some members of the species are better equipped to handle the costs of these handicaps.	Handicaps are honest signals.
2	While most biologists agree on the power of handicaps to maintain honest signaling, the question still debated is that of choice.	Is it a choice to use handicaps?
3	Are handicaps the result of a genetic condition that allows only certain members of the species to express the handicap fully?	Genetic condition?
4	Or do they happen when a more capable individual actively chooses to take on a visible hardship and therefore signal to others its underlying strength or abilities?	Or active choice?

	The word “equipped” in the passage is closest in meaning to	VOCABULARY. “Equipped” = prepared, enabled, armed.
✗	A exposed	Opposite to a large degree. “Exposed” = unprotected, unsheltered, vulnerable.
✗	B evolved	“Evolved” would mean that evolution did the preparing. That may be true in this case, but things can be equipped or prepared in other ways. “Evolved” is not a precise synonym for “equipped.”
✓	C prepared	Correct. “Some members of the species are better equipped to handle the costs” = some members are better prepared to handle the costs.
✗	D disarmed	Also somewhat opposite. “Disarmed” = deprived of weapons (arms).

	According to paragraph 5, biologists continue to argue over which of the following with regard to handicaps?	Fact. S2 indicates that the debate is about whether there is the choice behind the handicaps. S3–4 discuss the options: either genetics dictate who can display this kind of signal or individuals themselves choose to display on the basis of their own strength and ability.
✗	A Whether handicaps are an effective way to maintain honest signaling	Opposite. S2 says that biologists agree on this.
✗	B Whether some individuals are better able to handle the costs of handicaps	Biologists agree on this point as well, which is made in S1.
✗	C Whether all handicaps are honest signals	Biologists do not seem to be debating this point, also made in S1.
✓	D Whether capable individuals choose to take on handicaps	Correct. S2: “the question still debated is that of choice.” S3 poses one side of the debate (it’s genetically determined to use handicaps as signals), while S4 poses the other side (it’s an individual choice to do so).

	The word “underlying” in the passage is closest in meaning to	VOCABULARY. “Underlying” = fundamental, perhaps hidden under the surface but essential and real.
✗	A tremendous	Not quite. The individual would likely want to show “tremendous” (great or excessive) strength. However, great strength is not always hidden. These words are not synonyms.
✗	B physical	The individuals in question are likely indicating physical strength (as opposed to mental), but these words are not synonyms.
✗	C relative	Unrelated. When used as an adjective, the word “relative” typically means comparable, corresponding, or proportional.
✓	D inherent	Correct. “a more capable individual actively chooses to… signal to others its underlying strength” = a more capable individual chooses to signal its inherent or essential strength.

P6	Paragraph 6	Comments
S1	The condition-dependent model suggests that the level of display of a behavior or trait is directly proportional to genetic quality and environmental conditions and therefore cannot be faked.	Condition-dependent model: genetics + environment = cannot be faked.
2	Some point to bright, iridescent plumage of some bird species as a condition-dependent, and therefore honest, handicap.	Feather example.
3	Without limited physical wear, low parasite load, and a nutritious diet, these shiny feathers are impossible to maintain.
4	The choice model, alternatively, was advocated in 1990 by biologist Alan Grafen, who claimed that all animals have the option to display a large handicap, but each must choose whether and to what extent to display that handicap, according to its knowledge of its own ability level.	Choice model: all have option, but not all take it.
5	The optional signal remains honest because low-quality individuals will never signal at a level that is higher than would be advantageous for them, because of the increased cost of those signals.	Honest because signals are costly.

	What can be inferred from paragraph 6 about certain birds with shiny, iridescent feathers?	Inference. S2–3 discuss this example of shiny bird feathers.
✗	A They are choosing to maintain such feathers as a display.	S2: “Some point to bright, iridescent plumage of some bird species as a condition-dependent… handicap.” According to the passage, the condition-dependent model is opposed to the choice model (which is embraced in this answer choice).
✓	B They are honestly signaling their good health.	Correct. S2 states that these shiny feathers are a condition-dependent and honest handicap. S3 indicates that limited physical wear, low parasite load, and good nutrition support the bird’s ability to maintain these feathers. These attributes are all indicators of good health.
✗	C They are handicapped by low-nutrient diets.	Their diets are in fact “nutritious” (S3). In addition, the handicap is actually the display of feathers. This is a specialized meaning of “handicap” that is developed in the passage: a handicap is a visible, costly signal of strength that cannot be faked because it is so costly to maintain.
✗	D It is a low-cost signal that can be feigned.	S2: This signal is honest. That is, it cannot be feigned (= faked). Also, it is not low-cost.

	Which of the sentences below best expresses the essential information in the highlighted sentence in paragraph 3? Incorrect choices change the meaning in important ways or leave out essential information.	Simplify Sentence. S5 explains why a signal that is chosen is still honest. The reason is that weaker individuals will not choose high-cost signals.
✓	A Because weaker individuals will not choose costly signals, such signals must be honest.	Correct. This version properly simplifies the core ideas of S5.
✗	B Higher-quality individuals are the only ones capable of choosing and producing honest signals.	The original does not claim that only higher-quality individuals can choose and produce honest signals. Perhaps low-quality individuals can send other kinds of honest signals (besides these costly ones involving handicaps).
✗	C Weaker individuals will not survive if they choose to display costly signals.	This version exaggerates the impact on weaker individuals. The original states that weaker individuals will not choose to display costly signals. It never says that such individuals would actually die if they do make that choice.
✗	D A chosen signal cannot be considered honest if it does not have an increased cost.	The increased cost of a signal is a major reason why it can be considered honest. But the idea of the original sentence is not as general as it is presented in this version. The original is only justifying why chosen costly signals can be considered honest.

	Whole Passage	Comments
P1	There is a history of controversy within evolutionary biology over why honesty exists in animal communication…	Why is animal communication honest? All animals communicate. Communication = send + receive signals. Examples.
P2	In some cases, a signal may be honest, meaning that the sender is conveying accurate information, but signals can also be dishonest when the sender is providing false information to a receiver…	Honest and dishonest signals. All signals are costly. Examples.
P3	Biologists have found that, in general, animals communicate with honest signals, but why?…	Why are animals honest? Lying seems useful (in short run). Example of dishonest fiddler crab. Scientists: signals must generally be honest, or they’ll stop working. Handicap = high-cost signal = more believable.
P4	The handicap principle relies on the assumption that prominent signals of fighting ability or selection may be impossible, or impossibly costly, to fake…	Handicap principle: prominent signals can’t be faked. Example of elk antlers. Only strong can grow. Example of peacock tail. Only strong can deal with the handicap. Both examples: the signal of strength is the costly handicap.
P5	Thus, these revealing handicaps are honest signals of strength in the sense that some members of the species are better equipped to handle the costs of these handicaps…	Handicaps are honest signals. Is it a choice to use handicaps? Genetic condition? Or active choice?
P6	The condition-dependent model suggests that the level of display of a behavior or trait is directly proportional to genetic quality and environmental conditions and therefore cannot be faked…	Condition-dependent model: genetics + environment = cannot be faked. Feather example. Choice model: all have option, but not all take it. Honest because signals are costly.

	The passage mentions which of the following as a dishonest signal?	Fact. The only mention of a dishonest signal is that of the fiddler crab’s replacement claw in P3.
✗	A A male peacock’s long ornamental tail feathers	These feathers are mentioned in P1 and P2. In P3, they are described as an “honest signal.”
✗	B The stotting behavior of a gazelle	This stotting behavior (= “spectacular leaping”) is mentioned in P1. It is not specifically described as either honest or dishonest. But the behavior is meant to indicate athletic prowess, and it seems impossible to engage in this behavior without actually having such prowess.
✗	C A bird chirping in response to a predator	This chirping is not described specifically as honest. But according to P2, it happens in response to the true presence of a predator. Faking is never mentioned. So this signal appears honest as well.
✓	D A fiddler crab’s regrown fighting claw	Correct. In P3, the short-term gains of deception are illustrated with the example of the fiddler crab’s claw. This is specifically described as a dishonest signal (S5).

P3	Paragraph 3	Comments
S1–2	Biologists have found that, in general, animals communicate with honest signals, but why? Deception would seem to provide short-term gains.
3	A For example, the male fiddler crab is known for its one large fighting claw, which it uses to compete for a mate with other male crabs.	Insertion here doesn’t work. No particular dishonest signal has been introduced yet.
4–5	B If a fiddler crab loses its claw in the fight, another claw that is lighter in weight and therefore less effective grows in its place. Although the crab can still scare off other mates with its new claw that is similar in size to the original, it is sending the dishonest signal to other males that it is strong and able to fight, although if challenged it would likely lose.	Inserting the new sentence here won’t work either. So far, the paragraph has not mentioned whether the claw is dishonest.
6–7	C Scientists theorize that signals must be honest on average, at least to a certain degree. If not, the intended receiver would eventually evolve to ignore the signal, rendering it useless.	Correct. S5 introduces the idea that the regrown claw is a dishonest signal. The new sentence can now refer back to that signal. Moreover, S6 can pick up from the new sentence, making the point that signals must be, on average, honest.
8	D In the early 1970s, biologist Amotz Zahavi proposed the handicap principle: honesty is maintained through handicaps, or high-cost signals, which are naturally more believable.	In this location, the “however” does not make sense. S6–7 agree with the inserted sentence: dishonest signals are rare, and honest ones are common.

	This dishonest signal, however, appears to be the exception. Where would the sentence best fit?	Insert Text. The inserted sentence begins with “This dishonest signal.” So the previous text must refer to this kind of signal. The new sentence also contains a “however,” meaning that the new sentence introduces a permanent turn in the road about dishonest signals: namely, that they “appear to be the exception.” So the prior sentence or sentences ought to be presenting a dishonest signal, and the following text should be discussing how most signals are actually honest.
✗	A Choice A
✗	B Choice B
✓	C Choice C	Correct.
✗	D Choice D

	Why animal signaling is typically honest is a question that many evolutionary biologists have tried to understand.	Summary. Correct answers must be clearly expressed in the passage. They must also be among the major points of the passage. They should tie as directly as possible to the summary given.
✗	a Because a weak individual is likely to have a less nutritious diet, its ability to produce a high-cost signal is reduced.	This particular case may hold for the example of a bird’s shiny feathers (P6). But having a less nutritious diet is a minor point in this passage.
✓	b All animals communicate with one another, both within and across species, through signals that carry some cost to send.	Correct. This is the main idea of P1 and P2.
✓	c It is unclear whether individuals choose to exhibit specific handicaps or whether only some individuals are genetically capable of so doing.	Correct. This is the primary question discussed in P5 and P6.
✗	d One typical purpose of signals that animals send to other members of their species is to indicate mating desirability.	Indicating mating desirability might be one reason for signals, but not necessarily “typically.” Moreover, this point is minor within the passage.
✓	e According to the handicap principle, honest signaling dominates because high-cost signals are more believable.	Correct. This is the main topic of discussion for P3 and P4.
✗	f By 1990, much of the debate over the issue of choice in animal signaling was resolved in favor of the condition-dependent model.	P6 indicates that the choice model was advocated in 1990, but not that the debate was resolved in either direction.