Mechanisms for recognizing kin are found throughout the plant and anim

Mechanisms for recognizing kin are found throughout the plant and animal kingdoms, regardless of an organism’s social or mental complexity. Improvements in the general understanding of these mechanisms have turned some biologists’ attention to the question of why kin recognition occurs at all. One response to this question is offered by the inclusive fitness theory, which was developed in the 1960s. The theory is based on the realization that an organism transmits its genetic attributes to succeeding generations not solely through its offspring, but more generally through all of its close relatives. Whereas the traditional view of evolution held that natural selection favors the continued genetic representation of individuals within a species that produce the greatest number of offspring, the inclusive fitness theory posits that natural selection similarly favors organisms that help their relatives, because doing so also increases their own total genetic representation. The theory has helped to explain previously mysterious phenomena, including the evolution of social insect species like the honeybee, most of whose members do not produce offspring and exist only to nurture relatives.

Inclusive fitness theory has also been applied usefully to new findings concerning cannibalism within animal species. Based on the theory, cannibals should have evolved to avoid eating their own kin because of the obvious genetic costs of such a practice. Spade-foot toad tadpoles provide an illustration. Biologists have found that all tadpoles of that species begin life as omnivores, feeding mainly on organic debris in their soon-to-be-dry pool in the desert, but that occasionally one tadpole eats another or eats a freshwater shrimp. This event can trigger changes in the tadpole’s physiology and dietary preference, causing the tadpole to become larger and exclusively carnivorous, feasting on other animals including members of its own species. Yet the cannibals have a procedure of discrimination whereby they nip at other tadpoles, eating non-siblings but releasing siblings unharmed. This suggests that the inclusive fitness theory offers at least a partial answer to why kin recognition develops. Interestingly, a cannibal tadpole is less likely to avoid eating kin when it becomes very hungry, apparently putting its own unique genetic makeup ahead of its siblings’.

But there may be other reasons why organisms recognize kin. For example, it has recently been found that tiger salamander larvae, also either omnivorous or cannibalistic, are plagued in nature by a deadly bacterium. Furthermore, it was determined that cannibal larvae are especially likely to be infected by eating diseased species members. The fact that this bacterium is more deadly when it comes from a close relative with a similar immune system suggests that natural selection may favor cannibals that avoid such pathogens by not eating kin. For tiger salamanders then, kin recognition can be explained simply as a means by which an organism preserves its own life, not as a means to aid in relatives’ survival.

1. Which one of the following most accurately expresses the main point of the passage?

(A) Some findings support the hypothesis that kin recognition emerged through natural selection because it increased organisms’ total genetic representation, but this hypothesis may not explain all instances of kin recognition.
(B) Current research supports the view that the mechanisms enabling the members of a species to recognize close relatives are as various as the purposes served by that ability.
(C) Recent research involving tiger salamanders undermines the hypothesis concerning the purpose of kin recognition that is espoused by traditional evolutionary theorists.
(D) New research involving tiger salamanders indicates that the traditional theory of natural selection is more strongly supported by the evidence than is thought by those who consider only the case of the spade foot toad tadpole.
(E) While traditional evolutionary theory was unable to account for the phenomenon of kin recognition, this phenomenon is fully explained by the inclusive fitness theory.



2. The passage states which one of the following about some spadefoot toad tadpoles?\

(A) They develop the ability to recognize fellow carnivores.
(B) They feed only upon omnivorous tadpoles.
(C) They change in body size when they become carnivores.
(D) Their carnivorousness constitutes an important piece of evidence that calls into question the inclusive fitness theory.
(E) Their carnivorousness would not occur unless it contributed in some way to the evolutionary success of the spadefoot toad species.



3. Based on the passage, the author would be most likely to agree with which one of the following statements about evolutionary explanations of kin recognition?

(A) It is impossible to understand the mechanisms underlying kin recognition until an evolutionary explanation of such recognition has been attained.
(B) Such explanations require no modifications to traditional evolutionary theory.
(C) For any such explanation to be fully adequate it should ignore the differences of social or mental complexity of the organisms whose abilities it is intended to explain.
(D) Kin recognition may have different evolutionary explanations in different species.
(E) No other evolutionary explanation can account for the wide diversity of unusual phenomena with the same success as the inclusive fitness theory.



4. Which one of the following most accurately describes the function of the last sentence of the second paragraph?

(A) to draw attention to behavior that further complicates the set of facts to be explained by any theory of natural selection that accounts for kin recognition
(B) to explain why cannibals in most species eat their kin less often than do cannibal spadefoot toad tadpoles
(C) to describe behavior that lends support to the account of kin recognition presented in the second paragraph
(D) to offer evidence that the behavior of cannibal spadefoot toad tadpoles is unexplainable
(E) to imply that the described behavior is more relevant to the issue at hand than is the immediately preceding material



5. The passage most strongly supports which one of the following statements about the mechanism by which cannibal spadefoot toad tadpoles recognize their kin?

(A) It is not dependent solely on the use of visual cues.
(B) It is neither utilized nor possessed by those tadpoles that do not become cannibalistic.
(C) It does not always allow a tadpole to distinguish its siblings from tadpoles that are not siblings.
(D) It is rendered unnecessary by physiological changes accompanying the dietary shift from omnivorousness to carnivorousness.
(E) It could not have developed in a species in which all members are omnivorous.



6. The passage states which one of the following about the mechanisms that enable organisms to recognize their close genetic relatives?

(A) The mechanisms are most easily explained if we assume that they have a similar purpose in all species regardless of the species’ social or mental complexities.
(B) The mechanisms have become more clearly understood, prompting interest in the purpose they serve.
(C) The mechanisms have become the focus of theoretical attention only since the 1960s.
(D) The detailed workings of these mechanisms must be better understood before their purpose can be fully explained.
(E) The mechanisms operate differently in different species even when they serve exactly the same function.



7. The information in the passage most strongly suggests that the fact that most honeybees exist only to nurture relatives

(A) was not known to be true before the 1960s
(B) can be explained only if we assume that these members are in turn nurtured by the relatives they nurture
(C) is what led most biologists to reject the traditional view of evolution
(D) calls into question the view that evolution proceeds by natural selection
(E) is difficult to explain without at least supplementing the traditional view of evolution with further explanatory hypotheses



8. Which one of the following would, if true, most help to undermine the author’s evaluation in the last sentence of the passage?
(A) Many tiger salamander larvae infected by the deadly bacterium are not cannibalistic.
(B) The factor that determines which tiger salamander larvae are carnivorous and which are omnivorous is not contained in the genetic makeup of the larvae.
(C) Kin recognition helps tiger salamanders avoid inbreeding that may be life-threatening to their offspring.
(D) Noncannibalistic tiger salamanders tend to produce fewer offspring than cannibalistic tiger salamanders.
(E) Cannibalistic tiger salamanders are immune to certain diseases to which noncannibalistic salamanders are not.